Lamellar Crystal Structure and Haldane Magnetism in NH4 VPO4 OH

A novel vanadium hydroxide-phosphate, NH4 VPO4 OH, was synthesized hydrothermally in V2 O5 -NH4 H2 PO4 -citric acid system at 230 °C. It was characterized by XRD, TG-DSC, SEM-EDX, FTIR and NMR spectroscopy. NH4 VPO4 OH is isostructural with NH4 GaPO4 OH and features edge-sharing chains of VO6 octahedra. These chains running along [010] direction of the unit cell are connected by phosphate tetrahedra to form infinite layers parallel to the (100) plane. Ammonium cations are embedded between the heteropolyhedral layers. According to the thermodynamic and NMR measurements supported by the first-principles calculations, NH4 VPO4 OH presents a rare case of Haldane spin system with spin S=1 based on V3+ ions.

NaGaPO4F - a KTiOPO4-structured solid sodium-ion conductor

Advanced ionic conductors are crucial for a large variety of contemporary technologies spanning solid state ion batteries, fuel cells, gas sensors, water desalination, etc. In this work, we report on a new member of KTiOPO4-structured materials, NaGaPO4F, with sodium-ion conductivity. NaGaPO4F has been obtained for the first time via a facile two-step synthesis consisting of a hydrothermal preparation of an ammonia-based precursor, NH4GaPO4F, followed by an ion exchange reaction with NaNO3. Its crystal structure was precisely refined using a combination of synchrotron X-ray powder diffraction and electron diffraction tomography. The material is thermally stable upon 450 °C showing no significant structural transformations or degradation but only a ∼1% cell volume expansion. Na-ion mobility in NaGaPO4F was investigated by a joint experimental and computational approach comprising solid-state nuclear magnetic resonance (NMR) and density functional theory (DFT). DFT and bond-valence site energy (BVSE) calculations reveal 3D diffusion of sodium in the [GaPO4F] framework with migration barriers amounting to 0.22 and 0.44 eV, respectively, while NMR yields 0.3-0.5 eV that, being coupled with a calculated bandgap of ∼4.25 eV, makes NaGaPO4F a promising fast Na-ion conductor.

Advantages of a Solid Solution over Biphasic Intercalation for Vanadium-Based Polyanion Cathodes in Na-Ion Batteries

The efficient operation of metal-ion batteries in harsh environments, such as at temperatures below -20 °C or at high charge/discharge rates required for EV applications, calls for a careful selection of electrode materials. In this study, we report advantages associated with the solid solution (de)intercalation over the two-phase (de)intercalation pathway and identify the main sources of performance limitations originating from the two mechanisms. To isolate the (de)intercalation pathway as the main variable, we focused on two cathode materials for Na-ion batteries: a recently developed KTiOPO4-type NaVPO4F and a well-studied Na3V2(PO4)2F3. These materials have the same elemental composition, operate within the same potential range, and demonstrate very close ionic diffusivities, yet follow different (de)intercalation routes. To avoid any interpretation uncertainties, we obtained these materials in the form of particles with merely identical morphology and size. A detailed electrochemical study revealed a much lower capacity and energy density retention for phase-transforming Na3V2(PO4)2F3 compared to NaVPO4F, which exhibits a single-phase behavior over a wide range of Na concentrations. The reasons for the inferior rate capability and temperature tolerance for the phase-separating Na3V2(PO4)2F3 material should be affiliated with slow phase boundary propagation. We hope that the comprehensive information on limiting factors provided for both mechanisms is useful for the further optimization of electrode materials toward a new generation of high-power and low-temperature metal-ion batteries.

α-TiPO4 as a Negative Electrode Material for Lithium-Ion Batteries

To realize high-power performance, lithium-ion batteries require stable, environmentally benign, and economically viable noncarbonaceous anode materials capable of operating at high rates with low strain during charge-discharge. In this paper, we report the synthesis, crystal structure, and electrochemical properties of a new titanium-based member of the MPO₄ phosphate series adopting the α-CrPO₄ structure type. α-TiPO₄ has been obtained by thermal decomposition of a novel hydrothermally prepared fluoride phosphate, NH₄TiPO₄F, at 600 °C under a hydrogen atmosphere. The crystal structure of α-TiPO₄ is refined from powder X-ray diffraction data using a Rietveld method and verified by electron diffraction and high-resolution scanning transmission electron microscopy, whereas the chemical composition is confirmed by IR, energy-dispersive X-ray, electron paramagnetic resonance, and electron energy loss spectroscopies. Carbon-coated α-TiPO₄/C demonstrates reversible electrochemical activity ascribed to the Ti³⁺/Ti²⁺ redox transition delivering 125 mAh g^-1 specific capacity at C/10 in the 1.0-3.1 V versus Li⁺/Li potential range with an average potential of ∼1.5 V, exhibiting good rate capability and stable cycling with volume variation not exceeding 0.5%. Below 0.8 V, the material undergoes a conversion reaction, further revealing capacitive reversible electrochemical behavior with an average specific capacity of 270 mAh g^-1 at 1C in the 0.7-2.9 V versus Li⁺/Li potential range. This work suggests a new synthesis route to metastable titanium-containing phosphates holding prospective to be used as negative electrode materials for metal-ion batteries.

Hydroxyl Defects in LiFePO4 Cathode Material: DFT+U and an Experimental Study

Lithium iron phosphate, LiFePO₄, a widely used cathode material in commercial Li-ion batteries, unveils a complex defect structure, which is still being deciphered. Using a combined computational and experimental approach comprising density functional theory (DFT)+U and molecular dynamics calculations and X-ray and neutron diffraction, we provide a comprehensive characterization of various OH point defects in LiFePO₄, including their formation, dynamics, and localization in the interstitial space and at Li, Fe, and P sites. It is demonstrated that one, two, and four (five) OH groups can effectively stabilize Li, Fe, and P vacancies, respectively. The presence of D (H) at both Li and P sites for hydrothermally synthesized deuterium-enriched LiFePO₄ is confirmed by joint X-ray and neutron powder diffraction structure refinement at 5 K that also reveals a strong deficiency of P of 6%. The P occupancy decrease is explained by the formation of hydrogarnet-like P/4H and P/5H defects, which have the lowest formation energies among all considered OH defects. Molecular dynamics simulation shows a rich structural diversity of these defects, with OH groups pointing both inside and outside vacant P tetrahedra creating numerous energetically close conformers, which hinders their explicit localization with diffraction-based methods solely. The discovered conformers include structural water molecules, which are only by 0.04 eV/atom H higher in energy than separate OH defects.

Plastic deformation as nature of femtosecond laser writing in YAG crystal

Longitudinal inhomogeneity of tracks inscribed in a YAG crystal and the statistics of nonlinear transmittance of the writing beam is studied under conditions of direct femtosecond laser writing in non-thermal mode. Nonlinear transmittance fluctuations inherent in the laser writing were discovered, and their correlation with track inhomogeneity is established. A model of femtosecond laser writing in crystals is built that includes three modes of plastic deformation in the laser impact zone. The modification threshold of the femtosecond direct laser writing is identified with reaching yield stress.

Solid state chemistry for developing better metal-ion batteries

Metal-ion batteries are key enablers in today’s transition from fossil fuels to renewable energy for a better planet with ingeniously designed materials being the technology driver. A central question remains how to wisely manipulate atoms to build attractive structural frameworks of better electrodes and electrolytes for the next generation of batteries. This review explains the underlying chemical principles and discusses progresses made in the rational design of electrodes/solid electrolytes by thoroughly exploiting the interplay between composition, crystal structure and electrochemical properties. We highlight the crucial role of advanced diffraction, imaging and spectroscopic characterization techniques coupled with solid state chemistry approaches for improving functionality of battery materials opening emergent directions for further studies.

The development of high performing metal-ion batteries require guidelines to build improved electrodes and electrolytes. Here, the authors review the current state-of-the-art in the rational design of battery materials by exploiting the interplay between composition, crystal structure and electrochemical properties.

Laser-induced cavities with a controllable shape in nanoporous glass

The formation of birefringent structures inside nanoporous glass by femtosecond laser pulses was investigated. The laser-modified region is shown to be a cavity whose shape depends on the number of pulses. The shape of the void cross section varied from circle to ellipse when increasing the number of pulses from one to three. A layer of non-porous dense glass was revealed around the cavity. The cross section of this layer is nearly circular, regardless of the cavity shape and number of pulses in the investigated range. The mechanism of elongated cavity formation based on aniostropic light scattering on the spherical cavity is proposed.

Titanium-based potassium-ion battery positive electrode with extraordinarily high redox potential

The rapid progress in mass-market applications of metal-ion batteries intensifies the development of economically feasible electrode materials based on earth-abundant elements. Here, we report on a record-breaking titanium-based positive electrode material, KTiPO4F, exhibiting a superior electrode potential of 3.6 V in a potassium-ion cell, which is extraordinarily high for titanium redox transitions. We hypothesize that such an unexpectedly major boost of the electrode potential benefits from the synergy of the cumulative inductive effect of two anions and charge/vacancy ordering. Carbon-coated electrode materials display no capacity fading when cycled at 5C rate for 100 cycles, which coupled with extremely low energy barriers for potassium-ion migration of 0.2 eV anticipates high-power applications. Our contribution shows that the titanium redox activity traditionally considered as "reducing" can be upshifted to near-4V electrode potentials thus providing a playground to design sustainable and cost-effective titanium-containing positive electrode materials with promising electrochemical characteristics.

α-VPO4: A Novel Many Monovalent Ion Intercalation Anode Material for Metal-Ion Batteries

In this paper, we report on a novel α-VPO₄ phosphate adopting the α-CrPO₄ type structure as a promising anode material for rechargeable metal-ion batteries. Obtained by heat treatment of a structurally related hydrothermally prepared KTiOPO₄-type NH₄VOPO₄ precursor under reducing conditions, the α-VPO₄ material appears stable in a wide temperature range and possesses an interesting "sponged" needle-like particle morphology. The electrochemical performance of α-VPO₄ as the anode material was examined in Li-, Na-, and K-based cells. The carbon-coated α-VPO₄/C composite exhibits 185, 110, and 37 mA h/g specific capacities respectively at the first discharge and around 120, 80, and 30 mA h/g at consecutive cycles at a C/10 rate. The considerable capacity drop after the first cycle in Li and Na cells is presumably due to irreversible alkali ion consumption taking place upon alkali-ion de/insertion. The EDX analysis of the recovered electrodes revealed an uptake of ∼23% of Na after the first discharge with significant cell parameter alteration validated by operando XRD measurements. In contrast to the known β-VPO₄ anode materials, both Li and Na de/insertion into the new α-VPO₄ proceed via an intercalation mechanism with the parent structural framework preserved but not via a conversion mechanism. The dimensionality of alkali-ion migration pathways and diffusion energy barriers was analyzed by the BVEL approach. Na-ion diffusion coefficients measured by the potentiostatic intermittent titration technique are in the range of (0.3-1.0)·10^-10 cm²/s, anticipating α-VPO₄ as a prospective high-power anode material for Na-ion batteries.

Ultrafast laser-induced nanogratings in sodium germanate glasses

We report ultrafast laser inscription of nanogratings possessing form birefringence in binary sodium germanate glasses in a wide range of Na₂O content from 3 to 22 mol.%. A minimal number of laser pulses required to induce noticeable form birefringence is shown to grow exponentially with Na₂O content in glass. Atomic force microscopy showed similarity of their periodical structure and period value to those in the nanogratings formed in fused silica. A sharp pulse duration threshold below which laser pulses do not induce nanogratings in the studied glasses has been revealed. Formation of a nanograting in 22Na₂O·78GeO₂ at the studied conditions is accompanied by crystallization of a surrounding submicron layer and partial crystallization inside the nanograting with precipitation of Na₂Ge₄O₉ crystals.

Ferroelectricity, ionic conductivity and structural paths for large cation migration in Ca10.5−xPbx(VO4)7 single crystals, x = 1.9, 3.5, 4.9

Crystal structure, thermal, ionic conductivity of large cations (Ca and Pb), dielectric and non-linear optical properties were investigated for Ca_10.5−xPb_x(VO₄)₇ single crystals (x = 1.9, 3.5, 4.9).

Direct femtosecond laser-induced formation of CdS quantum dots inside silicate glass

We report the one-step precipitation of CdS quantum dots in the volume of CdS-doped silicate glass under the focused femtosecond laser beam without additional heat treatment of glass. Femtosecond direct laser writing leads to the annular distribution of the precipitated CdS quantum dots in laser-written domain optical properties of which could be tuned by laser beam parameters. Increasing the laser pulse number to 10³ significantly enhances luminescence intensity in the domains, while further increasing up to 10⁶ pulses leads to luminescence quenching. A possible scenario for the formation and distribution of quantum dots is proposed.

3-bit writing of information in nanoporous glass by a single sub-microsecond burst of femtosecond pulses

We have found that a single sub-microsecond burst of femtosecond laser pulses produces a sub-micrometer cavity possessing the homogeneous birefringence with slow-axis orientation perpendicular to polarization of the laser beam in high-silicate nanoporous glass. Retardance and the root mean square of slow-axis orientation are investigated in dependence on the energy and the number of pulses in the burst. A burst of just three pulses with 98 ns inter-pulse intervals has been shown to induce homogeneous birefringence, and a burst of four pulses has provided birefringence with retardance of 35 nm, which is sufficient for reliable readout of the information recorded with multilevel encoding in slow-axis orientation. A text file has been recorded and read out in an array of birefringent cavities, each carrying 3 bits of information. The sub-microsecond burst of femtosecond pulses paves the way for a multiple increase of the rate of digital information recording with multilevel encoding in glass.

Perspectives on Li and transition metal fluoride phosphates as cathode materials for a new generation of Li-ion batteries

To satisfy the needs of rapidly growing applications, Li-ion batteries require further significant improvements of their key properties: specific energy and power, cyclability, safety and costs. The first generation of cathode materials for Li-ion batteries based on mixed oxides with either spinel or rock-salt derivatives has already been widely commercialized, but the potential to improve the performance of these materials further is almost exhausted. Li and transition metal inorganic compounds containing different polyanions are now considered as the most promising cathode materials for the next generation of Li-ion batteries. Further advances in cathode materials are considered to lie in combining different anions [such as (XO4) (n-) and F(-)] in the anion sublattice, which is expected to enhance the specific energy and power of these materials. This review focuses on recent advances related to the new class of cathode materials for Li-ion batteries containing phosphate and fluoride anions. Special attention is given to their crystal structures and the relationships between structure and properties, which are important for their possible practical applications.

Synthesis and electrochemical performance of Li2Co1- x M x PO4F (M = Fe, Mn) cathode materials

In the search for high-energy materials, novel 3D-fluorophosphates, Li2Co1- x Fe x PO4F and Li2Co1- x Mn x PO4F, have been synthesized. X-ray diffraction and scanning electron microscopy have been applied to analyze the structural and morphological features of the prepared materials. Both systems, Li2Co1- x Fe x PO4F and Li2Co1- x Mn x PO4F, exhibited narrow ranges of solid solutions: x ≤ 0.3 and x ≤ 0.1, respectively. The Li2Co0.9Mn0.1PO4F material demonstrated a reversible electrochemical performance with an initial discharge capacity of 75 mA·h·g(-1) (current rate of C/5) upon cycling between 2.5 and 5.5 V in 1 M LiBF4/TMS electrolyte. Galvanostatic measurements along with cyclic voltammetry supported a single-phase de/intercalation mechanism in the Li2Co0.9Mn0.1PO4F material.

[Liquid crystal thermography in the diagnosis of acute appendicitis, cholecystitis and pancreatitis]

The authors have shown the diagnostic value of the coloured liquid crystal thermography on the basis of a comparative investigation of the data of clinical and thermographic studies, operation findings and histological studies in 223 patients with acute appendicitis, cholecystitis, pancreatitis and other diseases of organs of the abdominal cavity. The method is recommended for wide use in clinical practice.