With a purpose to clarify the reasons for the manifestation of high dielectric permittivity (e) of oxides with K2NiF4-type structure, the influences of pressure (up to 50 GPa) and thermobaric effects (T = 1273 K, P = 2.5 GPa) on the electrical properties of the appropriate La1.8Sr0.2Ni0.8Co0.2O4+delta oxide have been analyzed.Ceramic samples have been synthesized by the "solution combustion" method with diammonium citrate and subsequent sintering of pyrolysis products at 1473 K and thermobaric treatment (TBT). At room temperature, the dielectric constant of thermobarically treated ceramics was found to be an order of magnitude greater than e of sample obtained by sintering. Complex studies of electrical properties in broad ranges of pressure, temperatures and electric field frequencies have shown that the permittivity values of La1.8Sr0.2Ni0.8Co0.2O4+delta ceramics are not only due to external causes determined Maxwell-Wagner effects on grain boundaries and heterogeneity. Internal causes, the main of which are associated with bulk processes of charge polarization and distortion of polyhedra when the structure deviates from ideal, as well as with polarization processes caused by polaron carriers, are discussed. The baric behavior of thermo-electromotive (thermo-emf) force for some number of cycles of increasing and subsequent decreasing pressure makes it possible to use the examined material as a conductive medium capable of operating with controlled thermo-emf values under conditions of pressure change.

The electrical properties of the oxide Ce0.8Cu3V4O12 were studied at pressures up to 50 GPa. The samples have been synthesized by barothermal method. These compounds crystallize in the cubic symmetry with a perovskite-type structure. At ambient pressure in the temperature range from 10 to 300 K Ce0.8Cu3V4O12 - oxide has a metallic conductivity. Electrical resistance of the examined compounds measured at room temperature decreases when the pressure is raised from 16 to 50 GPa. There are two interval, where the resistance first falls rapidly with the pressure increase, and then the rate of the drop in resistance slows sharply. The baric dependencies of the magnetoresistance were obtained at the magnetic field up to 1 T. The values of the magnetoresistance are negative and amount 2% at pressure 22 GPa. The pressure range PT was determined, where a significant change of properties takes place. The results obtained for Ce0.8Cu3V4O12-oxide and the data of compounds ACu3V4O12 (A - Gd, Tb, Er, Tm) have been compared. A shift of the PT regions towards higher pressures with increasing serial number A was found. The manifestation of the effect of chemical contraction may be associated with a change in the crystal and electronic structure is assumed.

Министерство науки и высшего образования Российской Федерации Российское химическое общество им.Д.И.Менделеева Секция по химической термодинамике и термохимии Научного совета РАН по физической химии Сибирское Отделение Российской Академии Наук Институт неорганической химии им.А.В.Николаева СО РАН

Composites of (1-x)Gd2Zr2O7·xMgO were prepared by mixing gadolinium zirconate with freshly precipitated Mg(OH)2 followed by heat treatment at 1500 °C. Small concentrations of magnesium oxide dissolved in the complex oxide matrix of Gd2Zr2O7. This led to decrease in the lattice parameters of the matrix phase and a complex redistribution of Gd and Zr over the A and B sublattices. According to the impedance spectroscopy results of the studied samples, for (1-x)Gd2Zr2O7·xMgO (x = 0.05, 0.07, 0.10), the ionic conductivity was slightly higher than that for the undoped Gd2Zr2O7. The share of dominant ion transport did not change upon doping with magnesium oxide. The composites showed chemical resistance in a lithium halide (LiCl) melt and interacted with LiCl-xLi2O (x = 2 wt.%, 4 wt.%) melts at 650 °C with the formation of a Gd2O3 phase or a mixture of phases (Gd2O3, Li2ZrO3, ZrO2, LiGdO2, or LiGdCl2) on the ceramic surface, respectively.

The results of studying the effect of high pressures and high temperatures (8 GPa, 1273 K) used in the process of thermobaric treatment of CaCu3-xCoxTi4O12 ceramics (x = 0; 0.4; 0.6), initially prepared by solid-phase synthesis, on the structure and electrical characteristics are presented. The dielectric parameters were evaluated in a temperature interval (293-1000) K in a frequency range 1 Hz-32 MHz. It was established that the value of dielectric permittivity epsilon of samples upon thermobaric treatment is an order of magnitude higher than epsilon of samples prepared by solid-phase synthesis. The main reasons for the high values of dielectric permittivity are both the intragrain effects related, among other things, to hopping mechanism of polaron motion, and the polarization effects provided by the presence microstructure inhomogeneities. The latter are nonconducting boundaries of conducting grains and, in some examined materials, microscopic-scale surfaces of inhomogeneities, which appeared due to deformation during thermobaric treatment. At high temperatures, oxygen vacancies make the main contribution to the observed values of dielectric permittivity.

Glasses in xV(2)O(5)-(100-x)P2O5 system within x range from 35 to 95 mol% are obtained by a melt-quenching method and characterized by X-ray powder diffraction, atomic emission spectroscopy and red-ox titration. The dependences of density and molar volume of glasses on V2O5 concentration are linear up to 90 mol% of vanadium oxide and can be expressed via formulas: rho = 2.64 + 0.36.xV(2)O(5) g cm(-1) and V-mol/ = 54.17 + 6.36.xV(2)O(5) cm(3) mol(-)(1). The electronic conductivity of glasses is measured by both impedance spectroscopy and direct current methods. The glass composition of 95V(2)O(5)center dot 5P(2)O(5) shows the highest electrical conductivity value of similar to 1.0 x 10(-4) S cm(-1) at 50 degrees C. The concentration dependence of the conductivity is described at a qualitative level with non-constant force field molecular dynamics.

Phosphor Ca2La6.8Eu1.2(SiO4)6O2−δ is obtained via coprecipitation and the nitrate-citrate pyrolysis method. The structure and phase composition of the synthesized apatite silicates are studied using XRD. The luminescence spectra of the sample are registered before and after pressing at pressures above 5 GPa. The magnetic properties are analyzed by means of ESR spectroscopy and vibration magnetometry. The concentrations of Eu2+ ions and constants (λ) of optical splitting between 7FJ levels in the initial sample, and in the sample after hot pressing, are calculated.

This study is devoted to the investigation of the high dielectric constant causes in complex oxides with a structure of the K2NiF4 type. A new thermobaric treated ceramics on the basis conjugate LaxSr2-xFexTi1-xO4 (x = 0.5, 0.7) solid solutions was synthesized and the study their structure, microstructure, magnetic and dielectric properties was performed. It is shown that antiferromagnetic interactions coexist with ferromagnetic, which become dominant towards to low temperatures; the appearance of two types of magnetic interactions may be related to the presence of magnetic ions of different valences. Different values of the dielectric constants epsilon are observed in wide region of frequencies 10-10(7) Hz. In obtained at ambient pressure LaxSr2-xFexTi1-xO4 (x = 0.5, 0.7) ceramics the highest permittivity e value is only 30-50 in the frequency range from 1 kHz to 1 MHz. After the samples treatment at 1273 K and P = 4 GPa during 5 min epsilon increases to 5-10(2)-10(3) at 293 K and independent of frequency in the range (10(2)-10(6)) Hz. At the temperature increase the permittivity as well increases and the e value becomes similar to 10(6) at, approximately, f = 100 Hz and T = 750 K. An obvious change of samples microstructure and polyhedra structure anisotropy in LaxSr2-xFexTi1-xO4 (x = 0.5, 0.7) was observed after the thermobaric treatment. Described in this article performed dielectric properties investigations indicate that possible reasons of the high-permittivity origin are specifics of layered structure, microstructure and charge polarization associated with it, Maxwell-Wagner polarization at the grain boundaries and inhomogeneities and small polaron hopping conduction mechanism.

We report the preparation of ceramics on the basis of solid-solutions La1,8Sr0,2Ni0,8Cu0,2O4 with K2NiF4-type structure by new method and systematically study their structure, morphologies, and dielectric properties. Different values of frequency-independent dielectric constants are observed at wide region of frequencies 10-10(7) Hz in the ceramics prepared before and after thermobaric treatment of the sample. The highest permittivity epsilon is of order 10(3) (at ambient temperature) in the frequency range from 1 kHz to 10 MHz after the sample treatment at 1000 degrees C and P = 4 GPa during 5 min. An obvious change of grain morphology and sufficient change of structural polyhedra anisotropy in La1,8Sr0,2Ni0,8Cu0,2O4 was observed during the thermobaric treatment. Results of the dielectric properties investigations indicate that possible reasons of the high-permittivity origin are specifics of layered structure and charge polarization associated with it, Maxwell-Wagner polarization at the grain boundaries and inhomogeneities and hopping conduction mechanism of small polaron.

A wet chemistry method is proposed for the facile and scalable synthesis of several members of trivanadates M2V3O8 (M = K, Rb, Cs, NH4 ) with the fresnoite-type of lattice, known formerly using the solid-state chemistry methods. Phase composition, morphology and porosity of microstructured samples are characterized using X-ray powder diffraction, FT-IR spectroscopy, and scanning electron microscopy. The same fabrication technique fails for synthesis of hypothetical compounds M2V3O8 (M = Li, Na), since yielding an amorphous product. DFT computational screening of all possible fresnoitic trivanadates determines the main peculiarities of their electronic structures and establishes the M cation size as basic factor of their thermodynamic stability, elucidating the enhanced stability of compounds with the larger cations.

Layered perovskite-like oxides LnSr2CuTiO6.5 (Ln = La, Nd, Pr) were prepared, of them, the Pr and Nd compounds were for the first time. Their crystal-chemical characteristics and dielectric properties were studied. The dielectric permeability of the compounds was shown to increase considerably after thermobaric treatment (TBT) due to the effects of temperature and high pressure on the anisotropy of interatomic distances in coordination polyhedra (Ln,Sr)О9, (Cu,Ti)О6, and (Ln,Sr)О12. All the oxides studied have an activation conductivity type.

Layered perovskite-like oxides LnSr2CuTiO6.5 (Ln = La, Nd, Pr) were prepared, of them, the Pr and Nd compounds were for the first time. Their crystal-chemical characteristics and dielectric properties were studied. The dielectric permeability of the compounds was shown to increase considerably after thermobaric treatment (TBT) due to the effects of temperature and high pressure on the anisotropy of interatomic distances in coordination polyhedra (Ln, Sr)O9, (Cu, Ti)O6, and (Ln, Sr)O12. All the oxides studied have an activation conductivity type.

CeCu3–xMnxV4O12 (x = 0–3) with perovskite-like structure are synthesized at high pressures and temperatures. Their crystal structures are characterized by X-ray diffraction (space group Im\(\bar 3\), Z = 2). The temperature dependences of their electroresistance are studied.

Lithium vanadium-borate glasses with the composition of 0.3Li2O–(0.7-x)B2O3–xV2O5 (x = 0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45, and 0.475) were prepared by melt-quenching method. According to differential scanning calorimetry data, vanadium oxide acts as both glass former and glass modifier, since the thermal stability of glasses decreases with an increase in V2O5 concentration. Fourier transform infrared spectroscopy data show that the vibrations of [VO4] structural units occur at V2O5 concentration of 45 mol%. It is established that the concentration of V4+ ions increases exponentially with the growth of vanadium oxide concentration. Direct and alternative current measurements are carried out to estimate the contribution both electronic and ionic conductivities to the value of total conductivity. It is shown that the electronic conductivity is predominant in the total one. The glass having the composition of 0.3Li2O-0.275B2O3-0.475V2O5 shows the highest electrical conductivity that has the value of 7.4 × 10−5 S cm−1 at room temperature.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Perovskite-like phases AMn3V4O12 (A = Ca, Ce, and Sm) were prepared under borothermic conditions (p = 7.0–9.0 GPa, T = 700–1100°C). Their X-ray diffraction structure (space group Im \(\bar 3\) , Z = 2) was determined, and unit cell parameters were calculated: for CaMn3V4O12: а = 7.40824(3) Å, for SmMn3V4O12: а = 7.45280(8) Å, and for CeMn3V4O12: а = 7.46965(4) Å. The temperature-dependent electrical resistivity (10–300 K) and magnetic susceptibility (2–300 K) of the prepared phases were studied.