Formation, Stability, and Crystallinity of Various Tricalcium Aluminate Polymorphs

Tricalcium aluminate is an important phase of Portland clinker. In this paper, three polymorphs of C3A were prepared by means of the solid-state synthesis method using intensive milling of the raw material mixture which was doped with various amounts of Na2O and sintered at a temperature of 1300 °C for 2 h. The final products were evaluated through X-ray diffraction using Rietveld analysis. The effect of the Na dopant content on the change in the crystalline structure of tricalcium aluminate was studied. It was proven that the given preparation procedure, which differed from other studies, was close to the real conditions of the formation of Portland clinker, and it was possible to prepare a mixture of different polymorphs of calcium aluminate. Fundamental changes in the crystal structure occurred in the range of 3-4% Na, when the cubic structure changes to orthorhombic. At a dosage of Na dopant above 4%, the orthorhombic structure changes to a monoclinic structure. There are no clearly defined boundaries for the existence of individual C3A phases; these phases arise at the same time and overlap each other in the areas of their formation at different Na doses.

Seismic metasurface on an orthorhombic elastic half-space

The article is studying a seismic meta-surface in the case of an oscillatory system arranged on the surface of an orthorhombic elastic half-space. The approach is based on the asymptotic hyperbolic-elliptic formulation for the Rayleigh wave excited by prescribed surface loading. The latter results in hyperbolic equations for surface displacements, with the right-hand sides involving the loading components. The derived model allows a formulation for the meta-surface in the form of a periodic spring-mass system attached to the surface as a hyperbolic equation for the horizontal displacement, with smooth contact stresses emerging from averaging the effect of a regular array of oscillators. The associated dispersion relation is constructed and illustrated numerically for both cases of exponential and oscillatory decay.

Origin of Ferroelectricity in BiFeO3-Based Solid Solutions

We investigate the origin of ferroelectricity in the BiFeO₃-LaFeO₃ system in rhombohedral R3c and tetragonal P4mm symmetries by ab initio density functional theory calculations and compare their electronic features with paraelectric orthorhombic Pnma symmetry. We show that a coherent accommodation of stereo-active lone pair electrons of Bi is the detrimental factor of ferroelectricity. A Bloch function arising from an indirect Bi_6p-Fe_3d hybridization mediated through O_2p is the primary origin of spontaneous polarization (P_s) in the rhombohedral system. In the orthorhombic system, a similar Bloch function was found, whereas a staggered accommodation of stereo-active lone pair electrons of Bi exclusively results in paraelectricity. A giant P_s reported in the tetragonal system originates from an orbital hybridization of Bi_6p and O_2p, where Fe-3d plays a minor role. The P_s in the rhombohedral system decreases with increasing La content, while that in the tetragonal system displays a discontinuous drop at a certain La content. We discuss the electronic factors affecting the P_s evolutions with La content.

Role of Oxygen Source on Buried Interfaces in Atomic-Layer-Deposited Ferroelectric Hafnia-Zirconia Thin Films

Hafnia-zirconia (HfO₂-ZrO₂) solid solution thin films have emerged as viable candidates for electronic applications due to their compatibility with Si technology and demonstrated ferroelectricity at the nanoscale. The oxygen source in atomic layer deposition (ALD) plays a crucial role in determining the impurity concentration and phase composition of HfO₂-ZrO₂ within metal-ferroelectric-metal devices, notably at the Hf_0.5Zr_0.5O₂ /TiN interface. The interface characteristics of HZO/TiN are fabricated via sequential no-atmosphere processing (SNAP) with either H₂O or O₂-plasma to study the influence of oxygen source on buried interfaces. Time-of-flight secondary ion mass spectrometry reveals that HZO films grown via O₂-plasma promote the development of an interfacial TiO_x layer at the bottom HZO/TiN interface. The presence of the TiO_x layer leads to the development of 111-fiber texture in HZO as confirmed by two-dimensional X-ray diffraction (2D-XRD). Structural and chemical differences between HZO films grown via H₂O or O₂-plasma were found to strongly affect electrical characteristics such as permittivity, leakage current density, endurance, and switching kinetics. While HZO films grown via H₂O yielded a higher remanent polarization value of 25 μC/cm², HZO films grown via O₂-plasma exhibited a comparable P_r of 21 μC/cm² polarization and enhanced field cycling endurance limit by almost 2 orders of magnitude. Our study illustrates how oxygen sources (O₂-plasma or H₂O) in ALD can be a viable way to engineer the interface and properties in HZO thin films.

Synthesis of Lead-Free CaTiO3 Oxide Perovskite Film through Solution Combustion Method and Its Thickness-Dependent Hysteresis Behaviors within 100 mV Operation

Perovskite is attracting considerable interest because of its excellent semiconducting properties and optoelectronic performance. In particular, lead perovskites have been used extensively in photovoltaic, photodetectors, thin-film transistors, and various electronic applications. On the other hand, the elimination of lead is essential because of its strong toxicity. This paper reports the synthesis of lead-free calcium titanate perovskite (CaTiO₃) using a solution-processed combustion method. The chemical and morphological properties of CaTiO₃ were examined as a function of its thickness by scanning electron microscopy, X-ray diffraction (XRD), atomic force microscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible spectrophotometry. The analysis showed that thicker films formed by a cumulative coating result in larger grains and more oxygen vacancies. Furthermore, thickness-dependent hysteresis behaviors were examined by fabricating a metal-CaTiO₃-metal structure. The electrical hysteresis could be controlled over an extremely low voltage operation, as low as 100 mV, by varying the grain size and oxygen vacancies.

Unveiling the Origin of Robust Ferroelectricity in Sub-2 nm Hafnium Zirconium Oxide Films

HfO₂-based ferroelectrics are highly expected to lead the new paradigm of nanoelectronic devices owing to their unexpected ability to enhance ferroelectricity in the ultimate thickness scaling limit (≤2 nm). However, an understanding of its physical origin remains uncertain because its direct microstructural and chemical characterization in such a thickness regime is extremely challenging. Herein, we solve the mystery for the continuous retention of high ferroelectricity in an ultrathin hafnium zirconium oxide (HZO) film (∼2 nm) by unveiling the evolution of microstructures and crystallographic orientations using a combination of state-of-the-art structural analysis techniques beyond analytical limits and theoretical approaches. We demonstrate that the enhancement of ferroelectricity in ultrathin HZO films originates from textured grains with a preferred orientation along an unusual out-of-plane direction of (112). In principle, (112)-oriented grains can exhibit 62% greater net polarization than the randomly oriented grains observed in thicker samples (>4 nm). Our first-principles calculations prove that the hydroxyl adsorption during the deposition process can significantly reduce the surface energy of (112)-oriented films, thereby stabilizing the high-index facet of (112). This work provides new insights into the ultimate scaling of HfO₂-based ferroelectrics, which may facilitate the design of future extremely small-scale logic and memory devices.

Effect of B-site Co substitution on the structure and magnetic properties of nanocrystalline neodymium orthoferrite synthesized by auto-combustion

Samples of cobalt-doped neodymium orthoferrite compounds, NdCoxFe1-xO3 (0.0 ≤ x ≤ 0.5) were synthesized via glycine auto-combustion between 250 and 300°C and calcined at 500°C for 2 h. X-ray diffraction showed that all compounds had an orthorhombic perovskite structure with space group Pbnm. Increasing cobalt doping gradually reduced the lattice parameters and contracted the unit cell volume. Both X-ray diffraction and scanning electron microscopy showed that the particles were spherical and in the nano-sized range (19-52 nm) with pores between grains. Vibrating sample magnetometry at room temperature indicated that NdFeO3 has a high coercive field (1950 Oe) and cobalt substitution for iron led to a decrease in the coercive field, saturation and remanent magnetization, which was as a result of decreased magnetic moments in the crystal and reduced canting of the FeO6 octahedra. The increase in magnetization and coercive fields with increase of Co was connected to the microstructure (bond lengths and angles, defects, pores, grain boundaries) and crystallite size. The compounds NdCoxFe1-xO3 show antiferromagnetism with weak ferromagnetism due to uncompensated non-collinear moments. These compounds could serve as prototypes for tuning the properties of magnetic materials (ferromagnetic and antiferromagnetic) with potential applications in data storage, logic gates, switches and sensors.

A Possible Percutaneous Penetration Pathway That Should Be Considered

The intercellular lipids in the stratum corneum form structures composed of ordered phases with orthorhombic and hexagonal hydrocarbon-chain packing structures and, in addition, a structure composed of a disordered fluid phase. Although the fluid phase plays an important role in percutaneous penetration, little attention has been paid to it in the literature thus far. Recently, a method to estimate the proportion of the fluid phase within the lipids of the stratum corneum was proposed and it was shown to reach about 80%. However, since that study assumed uniform extraction of the intercellular lipids from the stratum corneum, the analysis might give rise to an overestimation of the proportion of the lipids in the fluid phase. We developed a way to investigate the proportion of the lipids in the fluid phase by treating with ethanol, into which the lipids in the fluid phase might be dominantly dissolved. From the experiment we pointed out the possibility that the proportion of the lipids in the fluid phase reached more than 50% of the whole intercellular lipids. Therefore, the fluid-phase region in the intercellular lipid matrix should be taken into account when considering the percutaneous penetration mechanism.

Study of the Transformations of Micro/Nano-crystalline Acetaminophen Polymorphs in Drug-Polymer Binary Mixtures

This study elucidates the physical properties of sono-crystallised micro/nano-sized acetaminophen/paracetamol (PMOL) and monitors its possible transformation from polymorphic form I (monoclinic) to form II (orthorhombic). Hydrophilic Plasdone® S630 copovidone (S630), N-vinyl-2-pyrrolidone and vinyl acetate copolymer, and methacrylate-based cationic copolymer, Eudragit® EPO (EPO), were used as polymeric carriers to prepare drug/polymer binary mixtures. Commercially available PMOL was crystallised under ultra sound sonication to produce micro/nano-sized (0.2–10 microns) crystals in monoclinic form. Homogeneous binary blends of drug-polymer mixtures at various drug concentrations were obtained via a thorough mixing. The analysis conducted via the single X-ray crystallography determined the detailed structure of the crystallised PMOL in its monoclinic form. The solid state and the morphology analyses of the PMOL in the binary blends evaluated via differential scanning calorimetry (DSC), modulated temperature DSC (MTDSC), scanning electron microscopy (SEM) and hot stage microscopy (HSM) revealed the crystalline existence of the drug within the amorphous polymeric matrices. The application of temperature controlled X-ray diffraction (VTXRPD) to study the polymorphism of PMOL showed that the most stable form I (monoclinic) was altered to its less stable form II (orthorhombic) at high temperature (>112°C) in the binary blends regardless of the drug amount. Thus, VTXRD was used as a useful tool to monitor polymorphic transformations of crystalline drug (e.g. PMOL) to assess their thermal stability in terms of pharmaceutical product development and research.