Room-temperature ferromagnetism in transparent transition metal-doped titanium dioxide

Study of the magnetism of C-doped MgO based on first-principles calculations and the Ising model

The electronic and magnetic properties of d0 dilute magnetic semiconductors formed by rock-salt structured magnesium oxide (MgO) doped with C are systematically studied based on first-principles calculations and the Ising model. It is shown that the electronic holes of p states are generated due to the impurity carbon replacing oxygen in MgO, and the magnetic moment of 2μB is introduced by each C impurity. The polarization energy and formation energy of C-doped MgO are calculated, and the magnetization energy of C-doped MgO is also calculated which is used to obtain the exchange constant between C impurities. By means of the Ising model, we simulated the magnetization and the susceptibility of the doped system with increasing temperature and obtained the Curie temperature of C-doped MgO.

Observation of Ferromagnetism in Dilute Magnetic Halide Perovskite Semiconductors

Dilute magnetic semiconductors (DMSs) have attracted much attention because of their potential use in spintronic devices. Here, we demonstrate the observation of robust ferromagnetism in a solution-processable halide perovskite semiconductor with dilute magnetic ions. By codoping of magnetic (Fe2+) and aliovalent (Bi3+) metal ions into CH3NH3PbCl3 (MAPbCl3) perovskite, ferromagnetism with well-saturated magnetic hysteresis loops and a maximum coercivity field of 1280 Oe was observed below 12 K. The ferromagnetic resonance measurements revealed that the incorporation of aliovalent ions modulates the carrier concentration and plays an essential role in realizing the ferromagnetism in dilute magnetic halide perovskites. Magnetic ions are proposed to interact through itinerant charge carriers to achieve ferromagnetic coupling. Our work provides a new avenue for the development of solution-processable magnetic semiconductors.

Robust Magnetic Proximity Induced Anomalous Hall Effect in a Room Temperature van der Waals Ferromagnetic Semiconductor Based 2D Heterostructure

Developing novel high-temperature van der Waals ferromagnetic semiconductor materials and investigating their interface coupling effects with 2D topological semimetals are pivotal for advancing next-generation spintronic and quantum devices. However, most van der Waals ferromagnetic semiconductors exhibit ferromagnetism only at low temperatures, limiting the proximity research on their interfaces with topological semimetals. Here, an intrinsic, van der Waals layered room-temperature ferromagnetic semiconductor crystal, FeCr0.5 Ga1.5 Se4 (FCGS), is reported with a Curie temperature (TC ) as high as 370 K, setting a new record for van der Waals ferromagnetic semiconductors. The saturation magnetization at low temperature (2 K) and room temperature (300 K) reaches 8.2 and 2.7 emu g-1 , respectively. Furthermore, FCGS possesses a bandgap of ≈1.2 eV, which is comparable to the widely used commercial silicon. The FCGS/graphene 2D heterostructure exhibits an impeccably smooth and gapless interface, thereby inducing a robust van der Waals magnetic proximity coupling effect between FCGS and graphene. After the proximity coupling, graphene undergoes a charge carrier transition from electrons to holes, accompanied by a transition from non-magnetic to ferromagnetic transport behavior with robust anomalous Hall effect (AHE). Notably, the van der Waals magnetic proximity-induced AHE remains robust even up to 400 K.

Pushing the heterometal doping limit while preserving long-lived charge separation in a Ti-based MOF photocatalyst

This study explores the nature, dynamics, and reactivity of the photo-induced charge separated excited state in a Fe3+-doped titanium-based metal organic framework (MOF), xFeMIL125-NH2, as a function of iron concentration. The MOF is synthesized with doping levels x = 0.5, 1 and 2 Fe node sites per octameric Ti-oxo cluster and characterized by powder x-ray diffraction, UV-vis diffuse reflectance, atomic absorption, and steady state Fe K-edge X-ray absorption spectroscopy. For each doping level, time-resolved X-ray transient absorption spectroscopy studies confirm the electron trap site role of the Fe sites in the excited state. Time scan data reveal multiexponential decay kinetics for the charge recombination processes which extend into the microsecond range for all three concentrations. A series of dye photodegradation studies, based on the oxidative decomposition of Rhodamine B, demonstrates the reactivity of the charge separated excited state and the photocatalytic capacity of these MOF materials compared to traditional heterometal-doped semiconductor photocatalysts.

Realization of High Magnetization in Artificially Designed Ni/NiO Layers through Exchange Coupling

High-magnetization materials play crucial roles in various applications. However, the past few decades have witnessed a stagnation in the discovery of new materials with high magnetization. In this work, Ni/NiO nanocomposites are fabricated by depositing Ni and NiO thin layers alternately, followed by annealing at specific temperatures. Both the as-deposited samples and those annealed at 373 K exhibit low magnetization. However, the samples annealed at 473 K exhibit a significantly enhanced saturation magnetization exceeding 607 emu cm-3 at room temperature, surpassing that of pure Ni (480 emu cm-3 ). Material characterizations indicate that the composite comprises NiO nanoclusters of size 1-2 nm embedded in the Ni matrix. This nanoclustered NiO is primarily responsible for the high magnetization, as confirmed by density functional theory calculations. The calculations also indicate that the NiO clusters are ferromagnetically coupled with Ni, resulting in enhanced magnetization. This work demonstrates a new route toward developing artificial high-magnetization materials using the high magnetic moments of nanoclustered antiferromagnetic materials.

Spin-Polarization Strategy for Enhanced Acidic Oxygen Evolution Activity

Spin-polarization is known as a promising way to promote the anodic oxygen evolution reaction (OER), since the intermediates and products endow spin-dependent behaviors, yet it is rarely reported for ferromagnetic catalysts toward acidic OER practically used in industry. Herein, the first spin-polarization-mediated strategy is reported to create a net ferromagnetic moment in antiferromagnetic RuO2 via dilute manganese (Mn2+ ) (S = 5/2) doping for enhancing OER activity in acidic electrolyte. Element-selective X-ray magnetic circular dichroism reveals the ferromagnetic coupling between Mn and Ru ions, fulfilling the Goodenough-Kanamori rule. The ferromagnetism behavior at room temperature can be well interpreted by first principles calculations as the interaction between the Mn2+ impurity and Ru ions. Indeed, Mn-RuO2 nanoflakes exhibit a strongly magnetic field enhanced OER activity, with the lowest overpotential of 143 mV at 10 mA cmgeo -2 and negligible activity decay in 480 h stability (vs 200 mV/195 h without magnetic field) as known for magnetic effects in the literature. The intrinsic turnover frequency is also improved to reach 5.5 s-1 at 1.45 VRHE . This work highlights an important avenue of spin-engineering strategy for designing efficient acidic oxygen evolution catalysts.

Fabrication, Structural Properties, and Electrical Characterization of Polymer Nanocomposite Materials for Dielectric Applications

This research paper aims to fabricate flexible PVA/Cs/TiO₂ nanocomposite films consisting of polyvinyl alcohol (PVA), chitosan (Cs), and titanium oxide (TiO₂) for application in energy storage devices. The samples were analyzed using X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and energy dispersive X-ray (EDX) techniques. The impact of TiO₂ on the electrical impedance, conductivity, permittivity, and energy efficiency of the PVA/Cs was determined in a frequency range of 100 Hz to 5 GHz. The XRD, FTIR, and EDX results showed the successful fabrications of the PVA/Cs/TiO₂. The SEM and AFM images illustrated that the TiO₂ was loaded and distributed homogenously in PVA/Cs chains. In addition, the electrical conductivity was enhanced from 0.04 × 10^-7 S.cm^-1 of PVA/Cs to 0.25 × 10^-7 S.cm^-1 and 5.75 × 10^-7 S.cm^-1, respectively, for the composite PVA/Cs/0.01TiO₂ and PVA/Cs/0.1TiO₂, and the dielectric constant grew from 2.46 for PVA/Cs to 7.38 and 11.93, respectively. These results revealed that modifications were made to the produced films, paving the way for using the composite PVA/Cs/TiO₂ films in different energy applications, such as electronic circuits and supercapacitors.

Structural, optical and magnetic properties of pure and 3d metal dopant-incorporated SnO2 nanoparticles

Dilute magnetic oxide semiconductors doped with transition metals have attracted significant attention both theoretically and experimentally due to their interesting and debatable magnetic behavior. In this work, we investigated the influence of Fe, Co and Ni doping on the structural, optical and magnetic properties of SnO2 nanoparticles, which were produced via a simple sol-gel technique. Raman spectroscopy, XRD, XPS, TEM, FT-IR characterizations were performed to study the crystal structure and morphology of the pure and doped nanoparticles, which confirmed the tetragonal rutile structure of the SnO2 nanoparticles. The XPS analysis revealed the incorporation of divalent dopant ions in the host matrix. The Raman plots indicated the generation of the cassiterite crystal structure, structural disorder and oxygen vacancies in the pure and doped SnO2 nanoparticles. The UV-visible plots indicated a decrease in the bandgap for the doped SnO2 nanoparticles because doping introduced defect levels in the band gap. The photoluminescence study showed the creation of oxygen vacancies due to the doping of different charge states of dopants. The magnetic study based on varying the temperature and field of magnetization revealed the diamagnetic nature of SnO2 at 300 K and 5 K respectively, and the concurrence of ferromagnetic (FM) and paramagnetic (PM) nature in doped SnO2 nanoparticles. The bound polaron model was used to explain the co-existence of FM and PM behavior in all the doped SnO2 nanoparticles.

Magnetic Order, Electrical Doping, and Charge-State Coupling at Amphoteric Defect Sites in Mn-Doped 2D Semiconductors

Two-dimensional (2D) dilute magnetic semiconductors (DMSs) are attractive material platforms for applications in multifunctional nanospintronics due to the prospect of embedding controllable magnetic order within nanoscale semiconductors. Identifying candidate host material and dopant systems requires consideration of doping formation energies, magnetic ordering, and the tendency for dopants to form clustered domains. In this work, we consider the defect thermodynamics and the dilute magnetic properties across charge states of 2D-MoS₂ and 2D-WS₂ with Mn magnetic dopants as candidate systems for 2D-DMSs. Using hybrid density functional calculations, we study the magnetic and electronic properties of these systems across configurations with thermodynamically favorable defects: 2D-MoS₂ doped with Mn atoms at sulfur site (Mn_S), at two Mo sites (2Mn_Mo), on top of a Mo atom (Mn-top), and at a Mo site (Mn_Mo). While the majority of the Mn-defect complexes provide trap states, Mn_Mo and Mn_W are amphoteric, although previously predicted to be donor defects. The impact of cluster formation of these amphoteric defects on magnetic ordering is also considered; both Mn_Mo-Mn_Mo (2Mn_2Mo) and Mn_W-Mn_W (2Mn_2W) clusters are found to be stable in ferromagnetic (FM) ordering. Interestingly, we observed the defect charge state dependent magnetic behavior of 2Mn_2Mo and 2Mn_2W clusters in 2D-TMDs. We investigate that the FM coupling of 2Mn_2Mo and 2Mn_2W clusters is stable in only a neutral charge state; however, the antiferromagnetic (AFM) coupling is stable in the +1 charge state. 2Mn_2Mo clusters provide shallow donor levels in AFM coupling and deep donor levels in FM coupling. 2Mn_2W clusters lead to trap states in the FM and AFM coupling. We demonstrate the AFM to FM phase transition at a critical electron density n^c_e = 3.5 × 10¹³ cm^-2 in 2D-MoS₂ and 2D-WS₂. At a 1.85% concentration of Mn, we calculate the Curie temperature of 580 K in the mean-field approximation.

A 2D material-based transparent hydrogel with engineerable interference colours

Transparent hydrogels are key materials for many applications, such as contact lens, imperceptible soft robotics and invisible wearable devices. Introducing large and engineerable optical anisotropy offers great prospect for endowing them with extra birefringence-based functions and exploiting their applications in see-through flexible polarization optics. However, existing transparent hydrogels suffer from limitation of low and/or non-fine engineerable birefringence. Here, we invent a transparent magneto-birefringence hydrogel with large and finely engineerable optical anisotropy. The large optical anisotropy factor of the embedded magnetic two-dimensional material gives rise to the large magneto-birefringence of the hydrogel in the transparent condition of ultra-low concentration, which is several orders of magnitude larger than usual transparent magnetic hydrogels. High transparency, large and tunable optical anisotropy cooperatively permit the magnetic patterning of interference colours in the hydrogel. The hydrogel also shows mechanochromic and thermochromic property. Our finding provides an entry point for applying hydrogel in optical anisotropy and colour centred fields, with several proof-of-concept applications been demonstrated.

Though transparent hydrogels with tunable optical anisotropy are attractive for soft robotics, wearable devices and optical applications, achieving large birefringence has been a challenge. Here, the authors report a transparent hydrogel with large, uniform and magnetically tunable birefringence.

KTaO3 -The New Kid on the Spintronics Block

Long after the heady days of high-temperature superconductivity, the oxides came back into the limelight in 2004 with the discovery of the 2D electron gas (2DEG) in SrTiO₃ (STO) and several heterostructures based on it. Not only do these materials exhibit interesting physics, but they have also opened up new vistas in oxide electronics and spintronics. However, much of the attention has recently shifted to KTaO₃ (KTO), a material with all the "good" properties of STO (simple cubic structure, high mobility, etc.) but with the additional advantage of a much larger spin-orbit coupling. In this state-of-the-art review of the fascinating world of KTO, it is attempted to cover the remarkable progress made, particularly in the last five years. Certain unsolved issues are also indicated, while suggesting future research directions as well as potential applications. The range of physical phenomena associated with the 2DEG trapped at the interfaces of KTO-based heterostructures include spin polarization, superconductivity, quantum oscillations in the magnetoresistance, spin-polarized electron transport, persistent photocurrent, Rashba effect, topological Hall effect, and inverse Edelstein Effect. It is aimed to discuss, on a single platform, the various fabrication techniques, the exciting physical properties and future application possibilities of this family of materials.

Titanium compounds containing naturally occurring dye molecules

A range of titanium compounds containing the naturally occurring dyes quinizarin (QH₂) and alizarin (AH₂) was synthesized and structurally characterized in the solid state. Among these is the first examples of a discrete metallocyclic arrangement formed exclusively using quinizarin ligands and the first examples of lanthanide containing titanium compounds of the alizarin family of ligands.

Morphology-Dependent Room-Temperature Ferromagnetism in Undoped ZnO Nanostructures

Since Dietl et al. predicted that Co-doped ZnO may show room-temperature ferromagnetism (RTFM) in 2000, researchers have focused on the investigation of ferromagnetic ZnO doped with various transition metals. However, after decades of exploration, it has been found that undoped ZnO nanostructures can also show RTFM, which in general is dependent on ZnO morphologies. Here, we will give an overall review on undoped ZnO nanomaterials with RTFM. The advanced strategies to achieve multidimensional (quasi-0D, 1D, 2D, and 3D) ferromagnetic ZnO nanostructures and the mechanisms behind RTFM are systematically presented. We have successfully prepared ferromagnetic nanostructures, including thin films, horizontal arrays and vertical arrays. The existing challenges, including open questions about quantum-bound ZnO nanostructures, are then discussed.

Increased room temperature ferromagnetism in Co-doped tetrahedral perovskite niobates

Dilute magnetic semiconductors (DMSs), such as (In, Mn)As and (Ga, Mn)As prototypes, are limited to III-V semiconductors with Curie temperatures (T c) far from room temperature, thereby hindering their wide application. Here, one kind of DMS based on perovskite niobates is reported. BaM x Nb(1-x)O3-δ (M = Fe, Co) powders are prepared by the composite-hydroxide-mediated method. The addition of M elements endows BaM x Nb(1-x)O3-δ with local ferromagnetism. The tetragonal BaCo x Nb(1-x)O3-δ nanocrystals can be obtained by Co doping, which shows strong saturation magnetization (M sat) of 2.22 emu g-1, a remnant magnetization (M r) of 0.084 emu g-1 and a small coercive field (H c) of 167.02 Oe at room temperature. The ab initio calculations indicate that Co doping could lead to a 64% local spin polarization at the Fermi level (E F) with net spin DOS of 0.89 electrons eV-1, this result shows the possibility of maintaining strong ferromagnetism at room temperature. In addition, the trade-off effect between the defect band absorption and ferromagnetic properties of BaM x Nb(1-x)O3-δ is verified experimentally and theoretically.

Dielectric Properties and Spectral Characteristics of Photocatalytic Constant of TiO2 Nanoparticles Doped with Cobalt

Dielectric properties and spectral dependence of the photocatalytic constant of Co doped P25 Degussa powder were studied. Doping of TiO₂ matrix with cobalt was achieved by precipitation method using of Tris(diethylditiocarbamate)Co(III) precursor (CoDtc–Co[(C₂H₅)₂NCS₂]₃). Five different Co contents with nominal Co/Ti atomic ratios of 0.005, 0.01, 0.02, 0.05 and 0.10 were chosen. Along with TiO₂:Co samples, a few samples of nanopowders prepared by Sol-Gel method were also studied. As it follows from XPS and NMR studies, there is a concentration limit (TiO₂:0.1Co) where cobalt atoms can be uniformly distributed across the TiO₂ matrix before metallic clusters start to form. It was also shown that CoTiO₃ phases are formed during annealing at high temperatures. From the temperature dependence of the dielectric constant it can be concluded that the relaxation processes still take place even at temperatures below 400 °C and that oxygen defect Ti–O octahedron reorientation take place at higher temperatures. The spectral dependency of the photocatalytic constant reveals the presence of some electronic states inside the energy gap of TiO₂ for all nanopowdered samples.

Relevance of Dispersion and the Electronic Spin in the DFT + U Approach for the Description of Pristine and Defective TiO2 Anatase

A density functional theory + U systematic theoretical study was performed on the geometry, electronic structure, and energies of properties relevant for the chemical reactivity of TiO2 anatase. The effects of D3(BJ) dispersion correction and the Hubbard U value over the energies corresponding to the TiO2/Ti2O3 reduction reaction, the oxygen vacancy formation, and transition-metal doping were analyzed to attain an accurate and well-balanced description of these properties. It is suggested to fit the Hubbard correction for the metal dopant atom by taking as reference the observed low spin-high spin (HS) energy difference for the metal atom. PBEsol-D3 calculations revealed a distinct electronic ground state for the yttrium-doped TiO2 anatase surface depending upon the type of doping and interstitial or substitutional defects. Based on the calculations, it was found that a HS state explains the observed ferromagnetism in cobalt-substituted TiO2 anatase. The results presented herein might be relevant for further catalytic studies on TiO2 anatase using a large surface model that would be worthwhile for heterogeneous catalysis simulations.

Tunable and Robust Near-Room-Temperature Intrinsic Ferromagnetism of a van der Waals Layered Cr-Doped 2H-MoTe2 Semiconductor with an Out-of-Plane Anisotropy

The intrinsically nonmagnetic feature of van der Waals (vdW) layered transition-metal dichalcogenide (TMDC) semiconductors limits the spintronic applications of these semiconductors. In this paper, we demonstrate a facile Te flux strategy to induce intrinsic ferromagnetism in the vdW layered 2H-MoTe₂ semiconductor by magnetic chromium (Cr) doping. The Curie temperature (T_c) and saturation magnetization (M_s) can be well tuned by adjusting the Cr doping concentration. A notable T_c up to 275 K can be achieved for the vdW layered Cr-doped 2H-MoTe₂ bulk crystals, which is much higher than that of recently reported van der Waals ferromagnetic semiconductors (T_c is mostly less than 70 K), in contrast to the diamagnetic feature of the pristine MoTe₂. Meanwhile, the highest M_s of the vdW layered Cr-doped 2H-MoTe₂ bulk crystals can reach 4.78 emu g^-1, which is stronger than most values reported for magnetic-element-doped van der Waals materials. In addition, all of the as-grown semiconducting Cr-doped 2H-MoTe₂ (Cr-2H-MoTe₂) single crystals display a large magnetic anisotropy with an out-of-plane easy axis of magnetization. The observed ferromagnetism in the Cr-2H-MoTe₂ has intrinsic characteristics, which can be mainly attributed to the spin polarization caused by Cr doping as confirmed by the density functional theory (DFT) calculations. Our approach offers an avenue to tune the ferromagnetism in the vdW layered semiconductor and explore its diverse spintronic and magnetoelectric applications.

Enhanced visible light photocatalytic activity of TiO2 co-doped with Fe, Co, and S for degradation of Cango red

The photocatalytic activity of TiO₂ was enhanced under visible light when it was co-doped with Fe, Co, and S through the sol-gel method. The resultant nano photocatalysts were characterized by XRD, EDX coupled with SEM, FT-IR, UV-Vis, and UV-DRS. The concentration ratio of precursor salts of Fe and S was kept at 1% each and of Co varied between 0.5% -1.5%. The photodegradation of Congo red was carried out and various factors like the concentration of catalyst, initial concentration of dye, pH, and irradiation time were also investigated to optimize the degradation process. Under optimized degradation conditions, 99.3% of Congo red (30 ppm) was degraded at slightly acidic pH, with 0.14 g of photocatalyst within 70 min of irradiation time.

Stoner Ferromagnetism in Hole-Doped CuMIIIAO2 with MIIIA = Al, Ga, and In

Using density functional theory calculations, we examine the effect of hole doping on the magnetic and electronic properties of CuMIIIAO2, with MIIIA = Al, Ga, and In. CuMIIIAO2 nonmagnetic semiconductors switch to ferromagnetic half-metals upon hole doping. For CuAlO2, the nonmagnetic-to-ferromagnetic transition occurs for hole densities of ∼7 × 1019/cm3. Ferromagnetism arises from an exchange splitting of the electronic states at the valence band edge, and it can be attributed to the high-lying Cu-d states. Hole doping induced by cation vacancies and substitutional divalent dopants is also investigated. Interestingly, both vacancies and nonmagnetic divalent dopants result in the emergence of ferromagnetism.

Colossal Magnetization and Giant Coercivity in Ion-Implanted (Nb and Co) MoS2 Crystals

Colossal saturation magnetization and giant coercivity are realized in MoS₂ single crystals doped with Nb and/or Co using an ion implantation method. Magnetic measurements have demonstrated that codoping with 2 at % Nb and 4 at % Co invoked a "giant" coercivity, as high as 9 kOe at 100 K. Doping solely with 5 at % Nb induces a "colossal" magnetization of 1800 emu/cm³ at 5 K, which is higher than that of metallic Co. The high magnetization is due to the formation of Nb-rich defect complexes, as confirmed by first-principles calculations. It is proposed that the high coercivity is due to the combined effects of strong directional exchange coupling induced by the Nb and Co doping and pinning effects from defects within the layered structure. This high magnetization mechanism is also applicable to 2D materials with bilayers or few layers of thickness, as indicated by first-principles calculations. Hence, this work opens a potential pathway for the development of 2D high-performance magnetic materials.

Tuning the Magnetism in Boron-Doped Strontium Titanate

The magnetic and electronic properties of boron-doped SrTiO₃ have been studied by first-principles calculations. We found that the magnetic ground states of B-doped SrTiO₃ strongly depended on the dopant-dopant separation distance. As the dopant–dopant distance varied, the magnetic ground states of B-doped SrTiO₃ can have nonmagnetic, ferromagnetic or antiferromagnetic alignment. The structure with the smallest dopant-dopant separation exhibited the lowest total energy among all configurations considered and was characterized by dimer pairs due to strong attraction. Ferromagnetic coupling was observed to be stronger when the two adjacent B atoms aligned linearly along the B-Ti-B axis, which could be associated with their local bonding structures. Therefore, the symmetry of the local structure made an important contribution to the generation of a magnetic moment. Our study also demonstrated that the O-Ti-O unit was easier than the Ti-B-Ti unit to deform. The electronic properties of boron-doped SrTiO₃ tended to show semiconducting or insulating features when the dopant–dopant distance was less than 5 Å, which changed to metallic properties when the dopant–dopant distance was beyond 5 Å. Our calculated results indicated that it is possible to manipulate the magnetism and band gap via different dopant–dopant separations.

The magnetism of titanium-defected undoped rutile TiO2: first-principles calculations

The physicochemical properties of TiO2 are largely dependent on the defects. Here, using first-principles calculations, we report a systematic investigation of the magnetic properties of Ti-defected rutile TiO2 systems. The results of our calculations show that the VTi concentration can significantly affect the size of the magnetism, and that the magnetism weakens with decreasing VTi concentration. Studies of phonon dispersion curves show that systems with lower VTi concentrations of 8.33% and 6.25% are kinetically stable. Further detailed calculations on the Ti11O24 system indicate that the magnetism mainly originates from four of the six nearest-neighbor O atoms to the Ti vacancy, but much less from the other two. The magnetic ground states are discussed, and the results show that for the Ti11O24 system, the ferromagnetic (FM) state of the four nearest-neighbor O atoms to the Ti vacancy is the magnetic ground state, and for the Ti22O48 system, the FM state of the two vacancies is the magnetic ground state. In addition, our calculations also indicate that the magnetic properties of Ti-defected TiO2 can be tuned via strain engineering. In general, this metal-defected TiO2 represents a novel kind of semiconductor. Research into the magnetic properties reported in this paper can enrich theoretical knowledge in this area and provide more potential candidates for TiO2-based materials.

Amorphous nonstoichiometric oxides with tunable room-temperature ferromagnetism and electrical transport

Material functionalities strongly depend on the stoichiometry, crystal structure, and homogeneity. Here we demonstrate an approach of amorphous nonstoichiometric inhomogeneous oxides to realize tunable ferromagnetism and electrical transport at room temperature. In order to verify the origin of the ferromagnetism, we employed a series of structural, chemical, and electronic state characterizations. Combined with electron microscopy and transport measurements, synchrotron-based grazing incident wide angle X-ray scattering, soft X-ray absorption and circular dichroism clearly reveal that the room-temperature ferromagnetism originates from the In_0.23Co_0.77O_1-v amorphous phase with a large tunable range of oxygen vacancies. The room-temperature ferromagnetism is tunable from a high saturation magnetization of 500 emu cm^-3 to below 25 emu cm^-3, with the evolving electrical resistivity from 5 × 10³ μΩ cm to above 2.5 × 10⁵ μΩ cm. Inhomogeneous nano-crystallization emerges with decreasing oxygen vacancies, driving the system towards non-ferromagnetism and insulating regime. Our work unfolds the novel functionalities of amorphous nonstoichiometric inhomogeneous oxides, which opens up new opportunities for developing spintronic materials with superior magnetic and transport properties.

The Use of Ultra-Small Fe3O4 Magnetic Nanoparticles for Hydrothermal Synthesis of Fe3+-Doped Titanate Nanotubes

A method of the hydrothermal synthesis of Fe³⁺-doped titanate nanotubes (TNT) is reported in which the ultra-small Fe₃O₄ nanoparticles are used as the sources of Fe³⁺ ions. The magnetic nanoparticles with a diameter of about 2 nm are added during the washing stage of the hydrothermal procedure. During washing, they gradually degrade and at the same time, the titanate product is transformed into nanotubes. The obtained nanotubes were characterized by structural and magnetic measurements. It was found that, depending on the value of the external magnetic field, they may show the property of room temperature ferromagnetism, paramagnetism or they may be diamagnetic. It was also shown that the modified TNTs have greater photocatalytic activity compared to unmodified TNTs.

Diffusion doping of cobalt in rod-shape anatase TiO2 nanocrystals leads to antiferromagnetism

Cobalt(ii) ions were adsorbed to the surface of rod-shape anatase TiO₂ nanocrystals and subsequently heated to promote ion diffusion into the nanocrystal. After removal of any remaining surface bound cobalt, a sample consisting of strictly cobalt-doped TiO₂ was obtained and characterized with powder X-ray diffraction, transmission electron microscopy, UV-visible spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy, SQUID magnetometry, and inductively-coupled plasma atomic emission spectroscopy. The nanocrystal morphology was unchanged in the process and no new crystal phases were detected. The concentration of cobalt in the doped samples linearly correlates with the initial loading of cobalt(ii) ions on the nanocrystal surface. Thin films of the cobalt doped TiO₂ nanocrystals were prepared on indium-tin oxide coated glass substrate, and the electrical conductivity increased with the concentration of doped cobalt. Magnetic measurements of the cobalt-doped TiO₂ nanocrystals reveal paramagnetic behavior at room temperature, and antiferromagnetic interactions between Co ions at low temperatures. Antiferromagnetism is atypical for cobalt-doped TiO₂ nanocrystals, and is proposed to arise from interstitial doping that may be favored by the diffusional doping mechanism.

Effect of Fe-doping on bending elastic properties of single-crystalline rutile TiO2 nanowires

Transition-metal-doping can improve some physical properties of titanium dioxide (TiO₂) nanowires (NWs), which leads to important applications in miniature devices. Here, we investigated the elastic moduli of single-crystalline pristine and Fe-doped rutile TiO₂ NWs using the three-point bending method, which is taken as a case study of impacts on the elastic properties of TiO₂ NWs caused by transition-metal-doping. The Young's modulus of the pristine rutile TiO₂ NWs decreases when the cross-sectional area increases (changing from 246 GPa to 93.2 GPa). However, the elastic modulus of the Fe-doped rutile NWs was found to increase with the cross-sectional area (changing from 91.8 GPa to 200 GPa). For NWs with similar geometrical size, the elastic modulus (156.8 GPa) for Fe-doped rutile NWs is 24% smaller than that (194.5 GPa) of the pristine rutile TiO₂ NWs. The vacancies generated by Fe-doping are supposed to cause the reduction of elastic modulus of rutile TiO₂ NWs. This work provides a fundamental understanding of the effects of transition-metal-doping on the elastic properties of TiO₂ NWs.

Conversion of Co Nanoparticles to CoS in Metal-Organic Framework-Derived Porous Carbon during Cycling Facilitates Na2S Reactivity in a Na-S Battery

Room-temperature sodium-sulfur batteries have attracted wide interest due to their high energy density and high natural abundance. Polysulfide dissolution and irreversible Na₂S conversion are challenges to achieving high battery performance. Herein, we utilize a metal-organic framework-derived Co-containing nitrogen-doped porous carbon (CoNC) as a catalytic sulfur cathode host. A concentrated sodium electrolyte based on sodium bis(fluorosulfonyl)imide, dimethoxyethane, and bis(2,2,2-trifluoroethyl) ether is used to mitigate polysulfide dissolution. We tune the amount of Co present in the CoNC carbon host by acid washing. Significant improvement in reversible sulfur conversion and capacity retention is observed with a higher Co content in CoNC, with 600 mAh g^-1 and 77% capacity retention for CoNC and 261 mAh g^-1 and 56% capacity retention for acid-washed CoNC at cycle 50 at 80 mAh g^-1. Post-mortem X-ray photoelectron spectroscopy, transmission electron microscopy, and selected area electron diffraction suggest that CoS is formed during cycling in place of Co nanoparticles and CoN₄ sites. Raman spectroscopy suggests that CoS exhibits a catalytic effect on the oxidation of Na₂S. Our findings provide insights into understanding the role Co-based catalysts play in sulfur batteries.

Magnetic ion oxidation state dependent magnetoelectric coupling strength in Fe doped BCT ceramics

Polycrystalline samples of Ba_0.96Ca_0.04Ti_0.91Fe_0.09O₃ were prepared using a conventional solid state reaction route with different Fe starting precursors (Fe₂O₃, Fe₃O₄). The Rietveld refined XRD data confirmed the phase purity and tetragonal crystal structure of both the samples. The average grain size measured using SEM was ≈0.40 μm in both the samples. XPS analysis confirmed the presence of only Fe²⁺ and both Fe²⁺/Fe³⁺ in Fe₂O₃ and Fe₃O₄ doped BCT samples. The P_r and M_r values have been measured to be 1.34 μC cm⁻², 2.88 μC cm⁻² and 0.0015 emu g⁻¹ and 0.135 emu g⁻¹ in Fe₂O₃ and Fe₃O₄ doped BCT samples, respectively. The Fe₃O₄ doped samples exhibit much better M-E coupling (≈22%) as compared to Fe₂O₃ (≈7%) doped BCT samples. The results obtained hence suggest that Fe₃O₄ doping in BCT is better suited for multiferroic applications.

Polycrystalline samples of Ba_0.96Ca_0.04Ti_0.91Fe_0.09O₃ were prepared using a conventional solid state reaction route with different Fe starting precursors (Fe₂O₃, Fe₃O₄). A significant difference in the magnetic and ferroelectric properties was observed.

Light-Activated Heterostructured Nanomaterials for Antibacterial Applications

An outbreak of a bacterial contagion is a critical threat for human health worldwide. Recently, light-activated heterostructured nanomaterials (LAHNs) have shown potential as antibacterial agents, owing to their unique structural and optical properties. Many investigations have revealed that heterostructured nanomaterials are potential antibacterial agents under light irradiation. In this review, we summarize recent developments of light-activated antibacterial agents using heterostructured nanomaterials and specifically categorized those agents based on their various light harvesters. The detailed antibacterial mechanisms are also addressed. With the achievements of LAHNs as antibacterial agents, we further discuss the challenges and opportunities for their future clinical applications.

Nano-Structured Dilute Magnetic Semiconductors for Efficient Spintronics at Room Temperature

In recent years, many efforts have been made to develop advanced metal oxide semiconductor nanomaterials with exotic magnetic properties for modern applications w.r.t traditional analogues. Dilute magnetic semiconductor oxides (DMSOs) are promising candidates for superior control over the charge and spin degrees of freedom. DMSOs are transparent, wide band gap materials with induced ferromagnetism in doping, with a minor percentage of magnetic 3d cation to create a long-range antiferromagnetic order. Although significant efforts have been carried out to achieve DMSO with ferromagnetic properties above room temperature, it is a great challenge that still exists. However, TiO2, SnO2, ZnO and In2O3 with wide band gaps of 3.2, 3.6, 3.2 and 2.92 eV, respectively, can host a broad range of dopants to generate various compositions. Interestingly, a reduction in the size of these binary oxides can induce ferromagnetism, even at room temperature, due to the grain boundary, presence of defects and oxygen vacancies. The present review provides a panorama of the structural analysis and magnetic properties of DMSOs based on binary metal oxides nanomaterials with various ferromagnetic or paramagnetic dopants, e.g., Co, V, Fe and Ni, which exhibit enhanced ferromagnetic behaviors at room temperature.

Core-Shell Structured Phenolic Polymer@TiO2 Nanosphere with Enhanced Visible-Light Photocatalytic Efficiency

Core–shell structured TiO₂ is a promising solution to promote the photocatalytic effectiveness in visible light. Compared to metal or semiconductor materials, polymers are rarely used as the core materials for fabricating core–shell TiO₂ materials. A novel core–shell structured polymer@TiO₂ was developed by using phenolic polymer (PP) colloid nanoparticles as the core material. The PP nanoparticles were synthesized by an enzyme-catalyzed polymerization in water. A subsequent sol–gel and hydrothermal reaction was utilized to cover the TiO₂ shell on the surfaces of PP particles. The thickness of the TiO₂ shell was controlled by the amount of TiO₂ precursor. The covalent connection between PP and TiO₂ was established after the hydrothermal reaction. The core–shell structure allowed the absorption spectra of PP@TiO₂ to extend to the visible-light region. Under visible-light irradiation, the core–shell nanosphere displayed enhanced photocatalytic efficiency for rhodamine B degradation and good recycle stability. The interfacial C–O–Ti bonds and the π-conjugated structures in the PP@TiO₂ nanosphere played a key role in the quick transfer of the excited electrons between PP and TiO₂, which greatly improved the photocatalytic efficiency in visible light.

Integration of amorphous ferromagnetic oxides with multiferroic materials for room temperature magnetoelectric spintronics

A room temperature amorphous ferromagnetic oxide semiconductor can substantially reduce the cost and complexity associated with utilizing crystalline materials for spintronic devices. We report a new material (Fe_0.66Dy_0.24Tb_0.1)₃O_7-x (FDTO), which shows semiconducting behavior with reasonable electrical conductivity (~500 mOhm-cm), an optical band-gap (2.4 eV), and a large enough magnetic moment (~200 emu/cc), all of which can be tuned by varying the oxygen content during deposition. Magnetoelectric devices were made by integrating ultrathin FDTO with multiferroic BiFeO₃. A strong enhancement in the magnetic coercive field of FDTO grown on BiFeO₃ validated a large exchange coupling between them. Additionally, FDTO served as an excellent top electrode for ferroelectric switching in BiFeO₃ with no sign of degradation after ~10¹⁰ switching cycles. RT magneto-electric coupling was demonstrated by modulating the resistance states of spin-valve structures using electric fields.

Tailoring the physical and chemical properties of Sn1-xCoxO2 nanoparticles: an experimental and theoretical approach

In this work, we present a coupled experimental and theoretical first-principles investigation on one of the more promising oxide-diluted magnetic semiconductors, the Sn_1-xCo_xO₂ nanoparticle system, in order to see the effect of cobalt doping on the physical and chemical properties. Our findings suggest that progressive surface enrichment with dopant ions plays an essential role in the monotonous quenching of the surface disorder modes. That weakening is associated with the passivation of the oxygen vacancies as the Co excess at the surface becomes larger. Room-temperature ¹¹⁹Sn Mössbauer spectroscopy data analysis revealed the occurrence of a distribution of isomer shifts, related to the different non-equivalent surroundings of Sn⁴⁺ ions and the coexistence of Sn²⁺/Sn⁴⁺ at the particle surfaces provoked by the inhomogeneous distribution of Co ions, in agreement with the X-ray photoelectron spectroscopy measurements. Magnetic measurements revealed a paramagnetic behavior of the Co ions dispersed in the rutile-type matrix with antiferromagnetic correlations, which become stronger as the Co content is increased. Theoretical calculations show that a defect with two Co mediated by a nearby oxygen vacancy is the most likely defect. The predicted effects of this defect complex are in accordance with the experimental results.

Enhanced Photocatalytic Activity of TiO2 Modified with GaI toward Environmental Application

Gallium (Ga) ion-doped TiO₂ (Ga-TiO₂) nanocomposite with small particle size (9-10 nm) and high surface area (104 m²/g) has been easily synthesized via sol-gel method at low temperature by using low-valent GaI as a doping precursor. The structural and morphological characterization of Ga-TiO₂ was carried out with standard analytical and spectroscopic techniques. Ga doping into the TiO₂ matrix inhibited a phase transformation from anatase to rutile (photocatalytically inactive) form, even at a higher temperature of 750 °C. Finally, Ga-TiO₂ nanocomposite showed high photocatalytic activity and exhibited 97% degradation of acid violet 63 dye within 60 min. The dye degradation rate constant was calculated as 1.6 × 10^-1 and 1.4 × 10^-1 min^-1 under UV and white light irradiation, respectively, which is higher, as compared to the previously reported Ga-TiO₂ composites to date.

UV/Vis Light Induced Degradation of Oxytetracycline Hydrochloride Mediated byCo-TiO2 Nanoparticles

Pharmaceuticals, especially antibiotics, constitute an important group of aquatic contaminants given their environmental impact. Specifically, tetracycline antibiotics (TCs) are produced in great amounts for the treatment of bacterial infections in both human and veterinary medicine. Several studies have shown that, among all antibiotics, oxytetracycline hydrochloride (OTC HCl) is one of the most frequently detected TCs in soil and surface water. The results of the photocatalytic degradation of OTC HCL in aqueous suspensions (30 mg·L⁻¹) of 0.5 wt.% cobalt-doped TiO₂ catalysts are reported in this study. The heterogeneous Co-TiO₂ photocatalysts were synthesized by two different solvothermal methods. Evonik Degussa Aevoxide P25 and self-prepared TiO₂ modified by the same methods were used for comparison. The synthesized photocatalysts were characterized by X-ray powder diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), UV/vis diffuse reflectance spectroscopy (DRS), and N₂ adsorption (BET) for specific surface area determination. The XRD and Raman results suggest that Ti⁴⁺ was substituted by Co²⁺ in the TiO₂ crystal structure. Uv/visible spectroscopy of Co-TiO₂-R showed a substantial redshift in comparison with bare TiO₂-R. The photocatalytic performance of the prepared photocatalysts in OTC HCL degradation was investigated employing Uv/vis spectroscopy and high-performance liquid chromatography (HPLC). The observed initial reaction rate over Co-TiO₂-R was higher compared with that of Co-TiO₂-HT, self-prepared TiO₂, and the commercial P25. The enhanced photocatalytic activity was attributed to the high surface area (153 m²·g⁻¹) along with the impurity levels within the band gap (2.93 eV), promoting the charge separation and improving the charge transfer ability. From these experimental results, it can be concluded that Co-doping under reflux demonstrates better photocatalytic performances than with the hydrothermal treatment.

Heterometal incorporation in NH2-MIL-125(Ti) and its participation in the photoinduced charge-separated excited state

X-ray spectroscopy studies reveal the location and role of Fe³⁺ sites incorporated in a Ti-based MOF exhibiting photo-induced charge separation.

Rare-earth-doped TiO2 rutile as a promising ferromagnetic alloy for visible light absorption in solar cells: first principle insights

The electronic structure and magneto-optic properties of TiO₂ (rutile) doped with two concentrations of rare-earth (RE) elements are explored using a first-principle all-electron full-potential augmented spherical-wave method based on the PBEsol–GGA approximation, to examine their potential use as a spintronic and optoelectronic system. The results predict that all compounds exhibit half-metallic character, the only exception is by doping with Nd or that the material is magnetic but the cloud is still a half-metallic magnet. We also found that the localized level at the Fermi energy shifts to lower energy as the atomic number of the 4f-element increases. Consequently, the mechanism that controls the ferromagnetism in these systems has been proposed according to this positioning. The energy of the localized level due to Gd is sufficiently low to lie at the top of the valence band, while Eu produces a midgap state. However, the Fermi level was not noticed precisely at the middle of the energy gap. In contrast, the impurity states of the Nd-, Pm-, and Sm-dopants are close to the bottom of the conduction band of the host system. This allows electrons to be delocalized, and gives a higher scattering cross-section. Interestingly, the analysis of optical absorption and electrical conductivity emphasizes that this ferromagnetic DMS based on rare-earth elements has the power to be a promising spintronic device for visible light absorption in solar cells. Finally, the relationship between the mechanism that controls the ferromagnetism and the absorption efficiency of visible light is discussed.

The electronic structure and magneto-optic properties of TiO₂ (rutile) doped with rare-earth elements are explored using a first-principles all-electron full-potential augmented spherical-wave method, to examine their potential use as a spintronic and optoelectronic system.

Combinatorial laser molecular beam epitaxy system integrated with specialized low-temperature scanning tunneling microscopy

We present a newly developed facility comprising a combinatorial laser molecular beam epitaxy system and an in situ scanning tunneling microscope (STM). This facility aims at accelerating the materials research in a highly efficient way by advanced high-throughput film synthesis techniques and subsequent fast characterization of surface morphology and electronic states. Compared with uniform films deposited by conventional methods, the so-called combinatorial thin films will be beneficial in determining the accurate phase diagrams of different materials due to the improved control of parameters such as chemical substitution and sample thickness resulting from a rotary-mask method. A specially designed STM working under low-temperature and ultrahigh vacuum conditions is optimized for the characterization of combinatorial thin films in an XY coarse motion range of 15 mm × 15 mm with submicrometer location precision. The overall configuration and some key aspects such as the sample holder design, scanner head, and sample/tip/target transfer mechanism are described in detail. The performance of the device is demonstrated by synthesizing high-quality superconducting FeSe thin films with gradient thickness and imaging surfaces of highly oriented pyrolytic graphite, Au (111), Bi₂Sr₂CaCu₂O_8+δ (BSCCO), and FeSe. In addition, we also have obtained clean noise spectra of tunneling junctions and the superconducting energy gap of BSCCO. The successful manufacturing of such a facility opens a new window for the next generation equipment designed for experimental materials research.

Fabrication and Study on Magnetic-Optical Properties of Ni-Doped ZnO Nanorod Arrays

Zn_1-xNi_xO nanorod arrays were prepared on Si substrates by magnetron sputtering and hydrothermal methods at 100 °C. We studied the effects of doped concentration and hydrothermal growth conditions on the crystal structure, morphology, photoluminescence, and magnetic properties of Zn_1-xNi_xO nanorod arrays. The research results show that the Zn_1-xNi_xO nanorod have the hexagonal wurtzite structure without the appearance of the second phase, and all samples have a highly preferred orientation of a (002) crystal face. The Zn_1-xNi_xO nanorod arrays exhibit obvious room temperature ferromagnetism with saturation magnetization at 4.2 × 10⁻⁴ emu/g, the residual magnetization is 1.3 × 10⁻⁴ emu/g and the coercive field is 502 Oe, and also excellent luminescent properties with seven times greater luminous intensity than that of ZnO nanorod arrays. The redshift of the ultraviolet emission peak was found by Ni²⁺ doping. We further explained the source and essence of the magnetic properties of Zn_1-xNi_xO nanorod arrays and deemed that the magnetic moment mainly comes from the hybrid electron exchange of O 2p and Ni 3d state.

Nonvolatile Control of the Electronic Properties of In2-xCrxO3 Semiconductor Films by Ferroelectric Polarization Charge

A series of Cr-doped In_2-xCr_xO₃ (ICO) semiconductor thin films were epitaxially grown on (111)-oriented 0.71Pb(Mg_1/3Nb_2/3)O₃-0.29PbTiO₃ (PMN-0.29PT) single-crystal substrates by the pulsed laser deposition. Upon the application of an electric field to the PMN-0.29PT substrate along the thickness direction, we realized in situ, reversible, and nonvolatile control of the electronic properties and Fermi level of the films, which are manifested by abundant physical phenomena such as the n-type to p-type transformation, metal-semiconductor transition, metal-insulator transition, crossover of the magnetoresistance (MR) from negative to positive, and a large nonvolatile on-and-off ratio of 5.5 × 10⁴% at room temperature. We also strictly disclose that both the sign and the magnitude of MR are determined by the electron carrier density of ICO films, which could modify the s-d exchange interaction and weak localization effect. Our results demonstrate that the ferroelectric gating approach using PMN-PT can be utilized to gain deeper insight into the carrier-density-related electronic properties of In₂O₃-based semiconductors and provide a simple and energy efficient way to construct multifunctional devices which can utilize the unique properties of composite materials.

Application and performance evaluation of a cost-effective vis- LED based fluidized bed reactor for the treatment of emerging contaminants

Visible light induced photocatalysis is considered as one of the most potential technologies which can achieve new levels of sustainability in water treatment. The current study explores the performance of immobilized visible light active catalyst on inert media for light driven catalysis of pharmaceuticals. These coated media is used in a continuous flow fluidized column reactor equipped with spirally arranged visible Light Emitting Diodes (LEDs) as irradiation source. The treatment efficiency of the system is evaluated for the removal of pharmaceutical drugs such as carbamazepine, diclofenac and ibuprofen. For the present study, system parameters such as light intensity and flow rate are optimized for maximum removal rate. The system shows complete elimination of the pharmaceuticals under the given experimental conditions. Complete mineralization of the target compounds are confirmed by TOC analysis. Recyclability is an important attribute for full scale commercialization of a treatment technology. An investigation on the reusability study of the photocatalyst displayed no significant reduction in the removal efficiency for a run of six cycles, hence rendering the photocatalyst reusable. The results acquired indicate an immense potential for scaling up the photoreactor as a sustainable tertiary treatment technology in water treatment plants.

Early Years of High-Throughput Experimentation and Combinatorial Approaches in Catalysis and Materials Science

This is a report on the early years of combinatorial materials science and technology. High-throughput technologies (HTTs) are found in life- and materials-science laboratories. Although HTTs have long been the standard in life sciences in academia as well as in industry, HTTs in materials science have become the standard in industry but not in academia. In life science, successful drugs developed with HTTs have been reported, but there is no information on successful materials developed with HTTs that have made it to the market. Some initial development of HTTs in materials science is summarized, especially early applications of artificial intelligence. This outlook attempts to summarize the development of combinatorial materials sciences from the early years to today.