The aspects of structure, dipole ordering, and ionic conductivity of the Na3Cr2(PO4)3 crystal with the four polymorphic phases (α, α', β, and γ) have been investigated. The features of the α-Na3Cr2(PO

This article investigates the structures and conductive properties of polycrystals of Na₃Fe₂(PO₄)₃ obtained by solid-state and melt synthesis methods using concentrated optical radiation. It has been established that in the melt synthesis method, the material is synthesized under significantly non-equilibrium thermodynamic conditions, leading to the creation of deformations in the sample, which contribute to the enhancement of ionic conductivity. Additionally, the synthesis duration is reduced by half. Through a comparative assessment of the structural parameters and conductive properties of these materials, it is demonstrated that polycrystals obtained by the melt method exhibit better texture and higher ionic conductivity. The occurrence of deformations during the synthesis of α-Na₃Fe₂(PO₄)₃ under high temperature-gradient conditions indicates the elasticity of the crystalline framework {[Fe₂(PO₄)]³⁻}_3∞. It is concluded that the non-equilibrium thermodynamic conditions of α-Na₃Fe₂(PO₄)₃ synthesis promote the formation of deformations in the crystalline structure of polycrystals, leading to a partial increase in symmetry and ionic conductivity.

X-ray diffraction and dielectric studies were performed on synthesized ceramic samples of the section (1–x) (0.8PbMg[ ]Nb[ ]O[ ]BiScO₃)⋅ x(0.8PbTiO[ ]BiScO₃) with [ ]–1 of the ternary BiScO₃–PbTiO₃–PbMg[ ]Nb[ ]O₃ (BS–PT–PMN) system, including the temperature dependence of thermally stimulated depolarization currents (TSDC). It was found that the samples are solid solutions with a perovskite structure, which have cubic symmetry in the range of x = 0–0.587 and tetragonal symmetry in the range of x = 0.680–1. In the intermediate composition range of x = 0.587–0.680 (morphotropic region — MR), the samples consist of a mixture of solid solutions of different symmetries. Data on the change in dielectric properties and TSDC(T) dependencies of solid solutions with a change in their composition were obtained. It was found that samples of compositions x =0–0.625 and 0.6875–1 exhibit relaxor-ferroelectric and conventional ferroelectric properties, respectively, while samples of compositions x = 0.625–0.6875 combine ferroelectric and relaxor-ferroelectric properties.

Problems of the dipole ordering and ionic conductivity of Na3Sc2(PO4)3 polycrystal that has three polymorphic phases—α, β, and γ—are studied. The features of the α-Na3Sc2(PO4)3crystal...

This article studies the influence of solid-phase (type 1 samples) and melt-quenching (type 2 samples) technological modes of obtaining Na₃Fe₂(PO₄)₃ polycrystals on their structures and ion-conducting properties. α-Na₃Fe₂(PO₄)₃ polycrystals of the 1st type are formed predominantly under an isothermal firing regime, and the synthesis of the 2nd type is carried out under sharp temperature gradient conditions, contributing to the formation of glassy precursors possessing a reactive and deformed structure, in which the crystallization of crystallites occurs faster than in precursors obtained under isothermal firing. The elemental composition of α-Na₃Fe₂(PO₄)₃ type 2 polycrystals is maintained within the normal range despite the sharp non-equilibrium thermodynamic conditions of synthesis. The microstructure of the type 1 Na₃Fe₂(PO₄)₃ polycrystals is dominated by chaotically arranged crystallites of medium (7–10 μm) and large (15–35 μm) sizes, while the polycrystals of type 2 are characterized by the preferential formation of small (3–4 μm) and medium (7–10 μm) crystallites, causing uniaxial deformations in their structure, which contribute to a partial increase in their symmetry. The advantage of type 2 polycrystals is that they have higher density and conductivity and are synthesized faster than type 1 samples by a factor of 4. The article also considers the issues of crystallization in a solid-phase precursor from the classical point of view, i.e., the process of the formation of small solid-phase nuclei in the metastable phase and their growth to large particles due to association with small crystallites using phase transitions. Possible variants and models of crystallite growth in Na₃Fe₂(PO₄)₃ polycrystals, as well as distinctive features of crystallization between two types of samples, are discussed.

In this paper influence of the excess Ca and Cu cations on the critical temperature (Tc) and critical transport current density (J_c) of high-temperature superconducting ceramics of the compositions (HTSC) Bi_1.6Pb_0.4Sr₂Ca_2.1Cu_3.1O_y, Bi_1.6Pb_0.4Sr₂Ca_2.25Cu_3.25O_y and Bi_1.6Pb_0.4Sr₂Ca₃Cu₄O_y synthesized by the glass-ceramic method has been studied. The synthesis of superconducting ceramics was carried out on the basis of the glass phase, obtained by ultra-fast quenching of the melt. Melting of the mixture of starting components was carried out without the use of a crucible under the influence of IR radiant heating. Analysis of the elemental composition of the samples of the initial precursors showed a significant deviation from stoichiometry in oxygen (increase), as well as a decrease in calcium content. The synthesis of HTSC ceramics was carried out at a temperature of 849–850 °C for 96 h with intermediate grinding every 24 h. Studies of the phase composition of ceramic samples by X-ray diffraction have shown that HTSC ceramics consist only of a superconducting high-temperature phase Bi-2223. Studies of current-carrying characteristics by the four-point probe method according to the criterion of 1 µV/cm² have shown that high-temperature superconducting ceramics of the compositions Bi_1.6Pb_0.4Sr₂Ca_2.1Cu_3.1O_y, Bi_1.6Pb_0.4Sr₂Ca_2.25Cu_3.25O_y and Bi_1.6Pb_0.4Sr₂Ca₃Cu₄O_y have an increased density of critical transport current of 9.12 A/cm², 7.62 A/cm² and 7.26 A/cm², respectively. At the same time, it was found that with a decrease in the content of Ca and Cu cations in HTSC ceramics, an increase in the critical current density is observed.