A layered perovskite-like oxides LaxSr2−xTi1−x/2Cux/2O4 (x = 0.2, 0.3, 0.5) with a K2NiF4-type structure were obtained. The introduction of copper into the titanium sublattice reduces the band gap. Copper in these materials serve as a photoactivity regulator and is presented in two oxidation states in accordance with optical, voltammetric and EPR data. LaxSr2−xTi1−x/2Cux/2O4 (x = 0.2) exhibits the greatest photoactivity in the oxidation of phenolic compounds and As(III) under the influence of UV and blue light; with increasing degree of substitution x, the photoactivity of LaxSr2−xTi1−x/2Cux/2O4 decreases. This is explained by the formation of a magnetic polaron, which is observed in LaxSr2−xTi1−x/2Cux/2O4 (x = 0.5) in the temperature range from 50 to 200 K and is proven by ESR method. The expansion of the spectral range of LaxSr2−xTi1−x/2Cux/2O4 to the visible region is explained by the formation of acceptor levels ( Cu^2 + + e^ - →Cu^ + / Cu^ + + h^ + →Cu^2 + ) in the band gap of Sr2TiO4, which increases the efficiency of separation of photogenerated electron–hole pairs. The presence of Cu (I) в LaxSr2−xTi1−x/2Cux/2O4 enhance photoactivity through the formation of active superoxygen radical on its surface ( Cu^ + + O_2( ad)→Cu^2 + +·O_2^ - ).

In this paper, for the first time, the dielectric properties studies on the layered perovskite-like oxide LaSr2CoMnO7-delta with the structure of the Ruddlesden-Popper series second homologue A(n+1)B(n)O(3n+1) (n = 2) were carried out. The ceramics samples were obtained by sintering in ambient pressure and under high pressure-high temperature conditions (40 kBar & 1173 K). The dielectric constant epsilon increases after thermobaric treatment from 500 to 5000, and epsilon is almost constant in the frequency range 10(3)-10(7) Hz. The dielectric loss tangent decreases after thermobaric treatment. It has been established that polaron conductivity plays a significant role in transport and polarization processes. An increase in the relaxation time of charge carriers in a thermobarically treated sample is consistent with an increase in dielectric constant, due to increased charge polarization because of greater distortion of structural polyhedra and Maxwell-Wagner polarization processes at the boundaries of inhomogeneities, the number of which increases after thermobaric effect.

Double perovskite Ba2CoNbO6, obtained by pyrolysis of nitrate-organic mixtures, was studied by XRD, XRF, DFT, AC/DC-magnetization, specific-heat, thermoelectric, and ESR methods. The sample has cubic symmetry space group Pm3m with a = b = c = 4.0074(11) & Aring;. Deficiency in oxygen ions shows the presence of Co ions in both 3+ and 2+ valency. According to AC-magnetization and specific-heat data, Ba2CoNbO6 demonstrates spin-glass ordering at TSG = 30 K at external field value of 0.1 kOe. This temperature of spin glass transition drops with field power increase down to complete suppression at 10 kOe. The effective magnetic moment determined using the Curie-Weiss approximation is 4.29 mu B, which is consistent with the theoretical estimation for Co ions in the intermediate-spin state. The peak at T = 90 K, observed in the temperature dependence of the specific heat and accompanied by a peak in the ESR linewidth, is possibly due to the structural transition at this temperature. The Seebeck coefficient of the compound is S = 4-6.5 mu V/K and the band gap obtained within the small-polaron-jump conductivity model is Delta E = 0.284 eV in the temperature range of 350-550 K connected with DFT calculation. An intensity ESR line, related to Co2+ ions, was observed in ESR spectra.

By pyrolysis of nitrate-organic mixtures, we synthesized double perovskite Sr2Fe0.6NbO5.4. We performed the study of the temperature dependencies of the EPR spectra, DC and AC magnetization, and magnetization isotherms in a wide temperature range of 4–300K. The EPR spectrum is described by the sum of two contributions below 125 K and indicates phase separation of the sample. The paramagnetic part of the inverse magnetic susceptibility is well approximated by the Curie–Weiss law with ΘCW≈−60 K. The exchange integrals between iron spins, calculated from the temperature dependence of the ESR integral intensity and the Curie–Weiss temperature, coincide and are equal to J/kB≈10 K. The negative sign of the Curie–Weiss temperature and the hysteresis loops indicate the antiferromagnetic canted nature of exchange interactions, which is further confirmed by the presence of a peak in the real part of the AC magnetization and its absence in the imaginary part.

layered perovskite-like oxides La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 ( x = 0.2, 0.3, 0.5) with a K 2 NiF 4 -type structure were obtained. The introduction of copper into the titanium sublattice reduces the band gap. Copper in these materials serve as a photoactivity regulator and is presented in two oxidation states in accordance with optical, voltammetric and EPR data. La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 ( x = 0.2) exhibits the greatest photoactivity in the oxidation of phenolic compounds and As(III) under the influence of UV and blue light; with increasing degree of substitution x , the photoactivity of La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 decreases. This is explained by the formation of a magnetic polaron, which is observed in La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 ( x = 0.5) in the temperature range from 50 to 200 K and is proven by ESR method. The expansion of the spectral range of La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 to the visible region is explained by the formation of acceptor levels ( Cu^2 + + e^ - →Cu^ + / Cu^ + + h^ + →Cu^2 + ) in the band gap of Sr 2 TiO 4 , which increases the efficiency of separation of photogenerated electron–hole pairs. The presence of Cu (I) в La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 enhance photoactivity through the formation of active superoxygen radical on its surface ( Cu^ + + O_2( ad)→Cu^2 + +·O_2^ - ).

Li3V2(PO4)3-based composites as a lithium-ion battery cathode material were synthesized by the hydrothermal method with subsequent annealing in an Ar atmosphere. The as-prepared samples were characterized by X-ray diffraction analysis and electron spin resonance (ESR) methods. Based on ESR, data the quantitative estimation of V4+ content was performed. The tetravalent vanadium ions arised instead of trivalent vanadium ions due to lithium nonstoichiometry in Li3V2(PO4)3 structure. This method of identifying nonstoichiometry via ESR detection of V4+ ions is very simple and demonstrative and can be used to characterize not only as-prepared samples but also samples after multiple electrochemical cycling. This technique of the lithium nonstoichiometry detection in Li3V2(PO4)3 can be used if the valence state of vanadium ions is stable and investigated samples are not degraded during a long time. To clarify the question, the additional ESR measurements were performed for Li3V2(PO4)3 samples which were air-stored over a long period (up to 2 years). The obtained data proved the sample degradation in the form of increasing in V4+ content. It was found that in the presence of LiPO3 salt in the composite the number of magnetic centers increased significantly, so it contributed to sample degradation, while the pure Li3V2(PO4)3 sample Li3V2(PO4)3/C were most stable.

Li3V2(PO4)3 cathodes for Li-ion batteries (LIBs) were synthesized using a hydrothermal method with the subsequent annealing in an argon atmosphere to achieve optimal properties. The X-ray diffraction analysis confirmed the material’s single-phase nature, while the scanning electron microscopy revealed a granular structure, indicating a uniform particle size distribution, beneficial for electrochemical performance. Magnetometry and electron spin resonance studies were conducted to investigate the magnetic properties, confirming the presence of the relatively low concentration and highly uniform distribution of tetravalent vanadium ions (V4+), which indicated low lithium deficiency values in the original structure and a high degree of magnetic homogeneity in the sample, an essential factor for consistent electrochemical behavior. For this pure phase Li3V2(PO4)3 sample, devoid of any impurities such as carbon or salts, extensive electrochemical property testing was performed. These tests resulted in the experimental discovery of a remarkably high lithium diffusion coefficient D = 1.07 × 10−10 cm2/s, indicating excellent ionic conductivity, and demonstrated impressive stability of the material with sustained performance over 1000 charge–discharge cycles. Additionally, relithiated Li3V2(PO4)3 (after multiple electrochemical cycling) samples were investigated using scanning electron microscopy, magnetometry and electron spin resonance methods to determine the extent of degradation. The combination of high lithium diffusion coefficients, a low degradation rate and remarkable cycling stability positions this Li3V2(PO4)3 material as a promising candidate for advanced energy storage applications.

The photocatalytic properties of single-phase sample Sr 2 Mn 0.4 Ti 0.6 O 4 is studied as a representative of a series of Sr2MnxTi1-xO4 2 Mn x Ti 1 - x O 4 solid solutions (x = 0.05, . 05 , 0.15, . 15 , 0.25, . 25 , 0 . 4 ) obtained by the SHS. The sample annealed at 1200 degrees C is characterized by a uniform distribution of Sr, Ti and Mn in the oxidation degree (4+) inside the aggregates, the average size of which does not exceed 1 mu m. According to UV-Vis-NIR spectroscopy data, a narrowing of the band gap of Sr2TiO4 2 TiO 4 from 3.16 to 1.8 eV is observed when it is doped with 40 mol% of manganese. This is due to the high photoactivity of Sr 2 Mn 0.4 Ti 0.6 O 4 in the HQ oxidation reaction in UV and blue light.

Magnetic and dielectric properties of Sr2MnTiO5.87 double perovskite have been studied. Magnetic phase transitions were observed at 12 and 43 K in the FC and ZFC curves of magnetization and magnetic heat capacity, the nature of which is being discussed. From the analysis of the lattice contribution to the specific heat, the Debye and Einstein temperatures were determined, which were θD = 217 К, θЕ1 = 275 К, θЕ2 = 615 К, θЕ3 = 2000 К.

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 double perovskite Sr2TiMnO5.87 was synthesized via the solution combustion precursor method using Sr(NO3)2, MnO2, i-Ti(OC3H7)4, and disubstituted ammonium citrate as a complexing agent. The crystal structure and unit cell parameters are refined by the Rietveld method using powder X-ray diffraction. The magnetic properties of double perovskites Sr2TiMnO5.87 were studied using the ESR spectroscopy, specific heat measurements in the temperature range ~ 5–300 K, and magnetometry under cooling in zero- (ZFC) and nonzero-fields (FC). The four ESR line were observed in ESR spectra, three ESR lines with g ~ 2 and fourth ESR at Bres = 50 mT in both X-and Q-bands measurements in the temperature range 37.5–42 K in Sr2TiMnO5.87. The peaks obtained in real and imaginary parts of AC magnetization measurements confirm phase separation at the same temperatures. The antiferromagnetic ordering was found out below the temperature TN ≈ 12 K. The fitting Debye and Einstein temperatures, obtained from the specific heat measurements, are equal to θD = 217 K, θE1 = 275 K, θE2 = 615 K, and θE3 = 2000 K.

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

The ceramic perovskite Sr2FeNbO6-δ was synthesized via the solution combustion precursor method. X-ray phase analysis showed that the sample is single-phase and does not contain impurities. The specific heat capacity and the Mössbauer spectra were measured for the Sr2FeNbO6-δ ceramic in the temperature range of 4–300 K. The observation of an asymmetric doublet in the Mössbauer spectra and the literature data on the magnetic susceptibility indicated the presence of two magnetic subsystems in Sr2FeNbO6-δ with antiferromagnetic exchange interactions. Based on the analysis of the temperature dependence of the specific heat capacity, we determined the Debye and Einstein temperatures.

A double perovskite Sr 2 CrNbO 6 powder compound was studied by using X-ray diffraction, AC and DC magnetization, and ESR measurements. Two transitions in antiferromagnetically ordered regimes were observed through magnetization measurements at T = 5 and 2 K and were confirmed by the linear dependence of the magnetization on the applied magnetic field at these temperatures, approximations of the temperature dependence of the ESR linewidth, and AC magnetization. The zero field cooling curve was approximated by Bonner–Fisher law for quasi one dimensional chain with the exchange integral J / k B = 1 K between chromium spins. An approximation of linear part of magnetic susceptibility temperature dependence was performed using Curie–Weiss law. To describe the obtained effective moment μ eff = 3.577μ B , the presence Cr 3+ and Cr 4+ ions is estimated at a respective ratio about 0.8 : 0.2.

A study is performed of the magnetic and dielectric properties of Sr2MnTiO5.87 double perovskite. The origin of the magnetic phase transitions observed in the FC and ZFC magnetization and magnetic specific heat curves at 12 and 43 K is discussed. The Debye and Einstein temperatures, determined by analyzing the lattice contribution to the specific heat, are found to be θD = 217 K, θЕ1 = 275 K, θЕ2 = 615 K, and θЕ3 = 2000 K.

: Li 3 V 2 (PO 4 ) 3 /Li 3 PO 4 (LVPO/LPO) composites as cathodes for Li-ion batteries were synthesized by the hydrothermal method and subsequently annealed in an Ar atmosphere. The effect of Li 3 PO 4 content on the crystal structure, morphology and the related magnetic and electrochemical properties of Li 3 V 2 (PO 4 ) 3 /Li 3 PO 4 composites, containing 7.5 wt% and 14 wt% of Li 3 PO 4 (LVPO/LPO-7.5 and LVPO/LPO-14) was investigated. The microstructure and morphology of the obtained composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM); magnetic and electrochemical properties investigations were performed using the electron spin resonance and galvanostatic methods, respectively. It was shown that Li 3 V 2 (PO 4 ) 3 /Li 3 PO 4 composites exhibit a high discharge capacity, good cycle performance (105 and 120 mAh g − 1 for the 200th cycle at 1C for LVPO/LPO-7.5 and LVPO/LPO-14, respectively), and insignificant changes in the surface morphology after 200 lithiation/delithiation cycles. Our results demonstrate that the increase in Li 3 PO 4 content led to a decrease in the Li stoichiometry and magnetic inhomogeneity in Li 3 V 2 (PO 4 ) 3 phase; thus, the improvement in the electrochemical performance of LVPO/LPO composites due to incorporation of Li 3 PO 4 can be attributed to their chemical and magnetic inhomogeneity.

CaCu3-xTi4-yFex+yO12 (1 or 3%) solid solutions were synthesized using a solid state method, while 1 or 3 mas. % of iron (natural abundance of isotopes) was added to the stoichiometric amount of CaO, CuO and TiO oxides. (CaCu3-xTi4-y Fex+yO12)-Fe-57 (3%) sample with a higher 57Fe isotope content was synthesized using the same tech-nology for the detailed investigation by the M6ssbauer spectroscopy. The structural and microstructural char-acteristics of calcium copper titanate samples were studied by X-ray diffraction, X-ray fluorescence analysis and scanning electron microscopy techniques. The magnetic properties were studied by M6ssbauer spectroscopy, electron spin resonance and magnetometry methods. Based on all experimental data we can conclude that Fe ions substitute Ti4+ and Cu(2+ )positions in octahedral and planar oxygen environment, respectively. Such type of substitution leads to the appearance of three types of iron magnetic centers: divalent Fe2+ in the planar envi-ronment and trivalent Fe3+ in the symmetrical and distorted octahedral positions that strongly effects to the magnetic properties of the investigated samples. Most unique magnetic properties including the metamagnetic phase transitions are observed in CaCu3-xTi4-yFex+yO12 (3%) sample where both the significant amount of Fe3+ ions in distorted octahedral position together with Fe2+ are present.

Li3V2(PO4)3/Li3PO4 (LVPO/LPO) composites as cathodes for Li-ion batteries were synthesized by the hydrothermal method and subsequently annealed in an Ar atmosphere. The effect of Li3PO4 content on the crystal structure, morphology and the related magnetic and electrochemical properties of Li3V2(PO4)3/Li3PO4 composites, containing 7.5 wt% and 14 wt% of Li3PO4 (LVPO/LPO-7.5 and LVPO/LPO-14) was investigated. The microstructure and morphology of the obtained composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM); magnetic and electrochemical properties investigations were performed using the electron spin resonance and galvanostatic methods, respectively. It was shown that Li3V2(PO4)3/Li3PO4 composites exhibit a high discharge capacity, good cycle performance (105 and 120 mAh g−1 for the 200th cycle at 1C for LVPO/LPO-7.5 and LVPO/LPO-14, respectively), and insignificant changes in the surface morphology after 200 lithiation/delithiation cycles. Our results demonstrate that the increase in Li3PO4 content led to a decrease in the Li stoichiometry and magnetic inhomogeneity in Li3V2(PO4)3 phase; thus, the improvement in the electrochemical performance of LVPO/LPO composites due to incorporation of Li3PO4 can be attributed to their chemical and magnetic inhomogeneity.