The properties of a Ca9La(VO4)7 single crystal were studied using dielectric spectroscopy and second-harmonic generation. The crystal structure of Ca9La(VO4)7 grown using the Czochralski technique was refined using single-crystal data. The distribution of Ca2+ and La3+ cations over structural positions was determined. The crystal structure refinement results were compared with those obtained previously from powder X-ray diffraction data. It was shown that the refinement carried out using two different data sets leads to approximately the same results for the distances in the polyhedra, but their distortion is significantly less in the case of using single-crystal data for calculation. Dielectric properties and conductivity measurements were performed on polished single-crystal wafers cut parallel and perpendicular to the c axis. Second-harmonic generation and dielectric temperature measurements revealed the presence of a reversible ferroelectric first-order phase transition at about 1224 K from the ferroelectric β-phase (space group R3c) to the paraelectric β′-phase. The ferroelectric–paraelectric phase transition is accompanied by a complex structural rearrangement, including a 60° rotation of the V1O4 tetrahedron, as well as slight displacements of the Ca2+ and La3+ cations. It has been shown that the conductivity differs only slightly along the polar axis and perpendicular to it. Above the phase transition temperature, the activation energy of the conductivity is the same for all directions, Ea~1.2 eV. The influence of composition on the phase transition temperature and the formation of ferroelectric and nonlinear optical properties is discussed.

New solid solutions of Sr9-xBaxIn(VO4)(7) (SBIV) and Sr9-xBaxYb(VO4)(7) (SBYV) with whitlockite-type structure were obtained by solid-phase synthesis within the ranges of 0 <= x <= 1.75 and 0 <= x <= 2, respectively. Incorporation of Ba2+ cations reduces phase transition temperatures from 959 K to 826 K for SBIV, and from 950 K to 800 K for SBYV. All synthesized samples showed nonlinear second harmonic generation (SHG) efficiency 10 times more than that of the quartz standard. SHG response remained largely constant as x increased. Sr2+ cation conductivity is suggested for both SBIV and SBYV. The incorporation of barium cations hinders the migration paths for Sr2+ cation. Barium atoms are located predominantly in the M3 position, which complicates the migration paths for strontium. The key result is creating a model for future finding of Sr-based ion conducting materials.

Solid solutions of the 0.7BiFeO 3 –0.3Ba 1-x Sr x TiO 3 system with compositions in the vicinity of the rhombohedral-cubic morphotropic phase boundary ( x ≤ 0.3) have been synthesized via solid state reactions. The crystal structure and morphology of the solid solutions have been studied using X-ray diffraction, scanning electron microscopy and Raman spectroscopy, and the chemical composition has been studied using energy dispersive X-ray spectroscopy. The dielectric properties of the compositions have been studied using impedance spectroscopy as a function of the concentration of strontium ions over a wide range of temperatures and frequencies. The structure of the solid solutions with x ≤ 0.3 contains coexisting rhombohedral and cubic phases, strontium ion substitution leading to higher cubic phase volume fraction. The x = 0 composition contains almost equal parts of coexisting phases, whereas the x > 0.25 solid solutions have single-phase cubic structures. The concentration-related changes in the phase structure of the solid solutions lead to a decrease in the lattice parameters of the coexisting phases and a nonmonotonic decrease in the electrical conductivity and the dielectric permeability of the compositions. The experimental data provide insight into specific changes of the structure and phase composition of the solid solutions in the vicinity of the rhombohedral-cubic morphotropic phase boundary and deliver better understanding of the relationship between the observed structural changes and the electrical properties of the compositions.

The purpose of this study was to investigate the effect of cation substitutions on the formation of Aurivillius phases at various annealing temperatures using solid-state synthesis. The phase formation of lanthanide bismuth ferrotitanates with the Aurivillius phase structure Ln(2)Bi(3)FeTi(3)O(15), where Ln = Tb, Ho, Er, Yb, has been studied. The obtained samples were characterized by X-ray diffraction, infrared spectroscopy, differential thermal and thermogravimetric analysis, and their elemental composition was studied. The predominant formation of a phase with a pyrochlore structure was revealed in the entire series studied in the chosen synthesis conditions. The exception was the sample containing ytterbium(III) cations, in which phases of the pyrochlore type and layered perovskite with the Aurivillius structure coexist. The main pyrochlore-type phase in all samples crystallizes in the cubic syngony. It is shown that in the Ln(2)Bi(3)FeTi(3)O(15) samples, where Ln = Tb, Ho, Er, the crystal lattice parameters decrease due to a decrease in the cationic radius of the Ln(III) ions. However, in the last sample of the studied series Yb2Bi3FeTi3O15, this pattern is violated because of Yb(III) ions distribution between the perovskite and pyrochlore phases. It has been established that the thermal effects observed in the samples Ln(2)Bi(3)FeTi(3)O(15), where Ln = Tb, Ho, Er, can be attributed to an order-disorder phase transition in the pyrochlore structure. When studying the temperature behavior of a two-phase sample of Yb2Bi3FeTi3O15, two reversible phase transitions were revealed: a low-intensity thermal effect characterizes changes in the pyrochlore-type structure, and a more intense thermal effect can be attributed to a ferroelectric phase transition in the structure of a layered perovskite of the Aurivillius family.

Powders and ceramics with whitlockite-type structure are synthesized using the solid-state method in novel Ca9-1.5xZnMeEux(PO4)(7) (Me = Li, Na) series, 0 <= x <= 1. The substances are divided to centro- and non-centrosymmetric by optical second harmonic investigation. There are non-centrosymmetry at x <= 0.3 and centrosymmetry at x >= 0.9, while at 0.3 < x < 0.9 they coexist. With differential scanning calorimetry and dielectric measurements, the reversible transformations in sequence R3c <-> R3c <-> R3m are observed and new phase transitions were found. At room temperature, photoluminescence spectroscopy and the M & ouml;ssbauer effect on Eu-151 nuclei pointed to reducing of number of Eu3+ non-equivalent positions from n = 3 in the phase R3c (x <= 0.3) to n = 2 in R3c at x = 1. The less positions for Eu3+ resulted in well-shaped luminescence spectra of increased intensity. Rietveld refinement evidenced that alkali atoms are settled in some extraordinal positions impeding Ca2+ ions hopping. This is consistent with the observed drop in ionic conductivity and better luminescence, probably, due to weakening of Eu3+ nonradiative phonon deactivation.

Ceramic samples of new compositions (1-x)(0.9NaNbO3 - 0.1BaTiO3) - xBaZrO3 (x = 0 divided by 0.05) modified by SiO2 oxide additive were prepared; their phase composition, structure parameters, microstructure, dielectric and ferroelectric properties were studied. Formation of a phase with a perovskite structure with a tetragonal unit cell was established, which volume increased due to partial replacement of A and B cations by Ba2+ and Zr4+ ones with large ionic radii. Decrease in the temperature of ferroelectric phase transitions and corresponding increase in polarization and electrocaloric effect indicates a positive effect of doping on the functional properties of sodium niobate-based ceramics.

The Na3Sc(PO4)(2) (NSPO) compound was obtained by solid-state synthesis method and has a new type of distorted beta-K2SO4 (arcanite) crystal structure that was refined based on powder XRD data in the space group (SG) P2(1)/c, with unit cell parameters: a = 11.5533(1) & Aring;, b = 5.31759(5) & Aring;, c = 16.7650(2) & Aring;, beta = 97.6439(6)degrees. The NSPO is a metastable phase with an optimal synthesis temperature range between 1173 and 1233 K. When a mixture of Na2CO3, NH4H2PO4 and Sc2O3 is annealed below this temperature range, the NaSICON-type compound and Na-polyphosphates is formed. However, annealing above T similar to 1245 K leads to the decomposition onset into the NaSICON-type compound (Na3Sc2(PO4)(3)), Na3PO4 and terminates at T similar to 1289 K. NSPO phase is dielectric with sigma(bulk) = 4.4 x 10(-7) S/cm at 300 K. Increasing the temperature from 300 to 1000 K leads to an increase in sigma(bulk) by four orders (sigma(bulk) = 5.6 x 10(-3) S/cm at 1000 K).

Single phase ceramic samples of new compositions (1 − x)NaNbO3 – хLiNbO3 (x = 0; 0.05; 0.10; 0.15), modified with a LiF additive, are prepared through solid state reactions, and their crystal structure, microstructure and dielectric and nonlinear optical properties are studied. A drop from 108.1 to 42.8 nm of the volume-weighted crystallite size distribution function corresponding to coherent scattering regions is observed. A rise in the temperature of phase transitions and a weakening of nonlinear optical properties are revealed as the concentration of Li cations grows.

Методом твердофазного синтеза получены однофазные керамические образцы новых составов: (1 – x )(K 0.5 Na 0.5 )NbO 3 ⋅ x BaZrO 3 ( x = 0–0.06), в том числе модифицированные добавками оксидов SiO 2 и ZnO, и изучены их кристаллическая структура, микроструктура, диэлектрические и нелинейные оптические свойства. Установлено формирование фазы со структурой перовскита с ромбической элементарной ячейкой во всех синтезированных образцах, зафиксировано увеличение объема элементарной ячейки в результате частичного замещения катионов базового состава на катионы комплексной добавки. Сегнетоэлектрические фазовые переходы подтверждены методами диэлектрической спектроскопии и генерации второй гармоники лазерного излучения. Выявлено понижение температуры фазовых переходов при допировании добавками оксидов SiO 2 и ZnO из сегнетоэлектрической ромбической фазы в сегнетоэлектрическую тетрагональную, затем – в кубическую параэлектрическую фазу.

— Single-phase (1 – x )(K 0.5 Na 0.5 )NbO 3 ⋅ x LiNbO 3 (KNN–LN) perovskite-structure ceramic materials with x = 0–0.10 modified with CuO and KCl additions have been prepared by solid-state synthesis, and their phase composition, structure, microstructure, and dielectric and ferroelectric properties have been studied. Increasing the percentage of lithium niobate has been shown to increase their Curie temperature and lower the temperature of their polymorphic phase transition, which is accompanied by a decrease in perovskite cell parameters, in accord with the ionic radii of the A-site cations. The x = 0.2 material has been found to have an increased room-temperature dielectric permittivity, which correlates with the observed increase in spontaneous polarization, as evidenced by laser radiation second harmonic generation intensity measurements.

Single-phase ceramic samples with new compositions (1 – x – у )(Na 0.5 Bi 0.5 )TiO 3 – х BaTiO 3 – у (K 0.5 Na 0.5 )NbO 3 ( x = 0.05, у = 0–0.15) modified with ZnO and GeO 2 additions were obtained by solid-phase synthesis. Their crystal structure, microstructure, and dielectric and local piezoelectric properties were studied. A phase with a perovskite structure with a pseudocubic unit cell was found to form in all of the synthesized samples; it was shown that the unit cell volume increased as a result of the partial replacement of base cations by complex additive cations. The ferroelectric phase transitions were confirmed by dielectric spectroscopy. Residual piezoelectric hysteresis loops were obtained for the synthesized samples in the polarization switching spectroscopy mode, which confirmed the switching of ferroelectric polarization.

— Single-phase (1 – x )(K 0.5 Na 0.5 )NbO 3 ⋅ x BaZrO 3 ( x = 0–0.06) ceramics with new compositions, including those modified with SiO 2 and ZnO oxide additions, have been prepared and their crystal structure, microstructure, and dielectric and nonlinear optical properties have been studied. A phase with the perovskite structure and an orthorhombic unit cell has been shown to form in all of the synthesized materials. Partial replacement of cations of the basic composition by cations of the combined additive has been demonstrated to cause an increase in unit-cell volume. The ferroelectric phase transitions in the ceramics have been confirmed by dielectric spectroscopy and laser radiation second harmonic generation measurements. Doping with SiO 2 and ZnO oxide additions has been shown to lower the temperatures of the transitions from the orthorhombic ferroelectric phase to a tetragonal ferroelectric one and then to a cubic paraelectric phase.

Single phase ceramic samples of new compounds (1 − x )(K 0.5 Na 0.5 )NbO 3 − x La(Ag 0.5 Sb 0.5 )O 3 ( x = 0–0.15), modified by metal oxide additives ZnO, CuO, and MnO 2 , are prepared via a solid state reaction. The crystal structure, microstructure, and dielectric and ferroelectric properties of the samples are studied. It is established that a phase with a perovskite structure and an orthorhombic unit cell formed in each sample. Ferroelectric phase transitions are confirmed via dielectric spectroscopy. Generation of the second harmonic is observed, along with a drop in the temperature of transitions from the ferroelectric orthorhombic phase to the ferroelectric tetragonal phase, and then to the cubic paraelectric phase.

Influence of (K0.5Bi0.5)TiO3 (KBT) dopants on crystal and microstructure, ferroelectric and dielectric properties of ceramic composition from morphotropic phase boundary in the system (1-x-y)(Na0.5Bi0.5)TiO3 - xBaTiO(3) - y (K0.5Bi0.5)TiO3 (x = 0.06, y = 0-0.15) additionally modified by ZnO additives was studied using a complex of methods. Changes from 42.8 nm to 62.6 nm of the volume-weighted crystallite size distribution function G(L) corresponding to coherent scattering regions were observed. The microstructure and the second harmonic generation data indicated a change in the relative content of polar nanoregions in tetragonal nonpolar matrix. Decrease in temperatures of phase transitions T (m) and T (d) was observed with KBT concentration increasing.

Single-phase ceramic samples of new compositions (Na 1 – х Sr х ) 0.5 Bi 0.5 TiO 3 ( x = 0–0.5), including those modified by additives of SiO 2 and ZnO oxides, have been obtained by solid-phase synthesis. The crystal structure and microstructure of these samples, as well as their dielectric, nonlinear optical, and local piezoelectric properties, have been studied. The formation of a perovskite-type phase with a pseudocubic unit cell in all synthesized samples and an increase in the cell volume as a result of partial substitution of perovskite structure cations are established. A decrease in the temperature of ferroelectric phase transitions (confirmed by the methods of dielectric spectroscopy and laser second-harmonic generation) to the tetragonal paraelectric phase is revealed. Remanent piezoelectric hysteresis loops are obtained for the synthesized samples in the polarization switching mode; this result confirms the occurrence of ferroelectric polarization switching.

Influence of cation substitution on phase content, crystal structure parameters, microstructure, and dielectric propertiesDielectric Properties of (1-x-y)(Na0.5Bi0.5)TiO3 –xBaTiO3 – y(K0.5Na0.5)NbO3 ceramics with x = 0.05, y = 0–0.15 and additionally modified by 1.5 w.% of ZnO was studied. The samples prepared by the solid-state reaction method are characterized by phase transitions with corresponding peaks of dielectric permittivity at ~550–600 K and anomalies near ~350–425 K. A decrease in the unit cell parameters changes was observed in modified compositions correlating with radii of substituting cations. A decrease in the temperatures of phase transitions Tm and Td was observed as well. Additionally, effects of dielectric relaxation caused by the formation of oxygen vacancies in ZnO-doped samples were observed at temperatures >700 K. An increase in the dielectric permittivity value at the room temperature was observed at y = 0.10 and at y = 0.05 in ZnO modified samples confirming prospect of functional properties improvement.

Influence of dopants on structure, microstructure, dielectric and ferroelectric properties of ferroelectric-relaxor (Na0.5Bi0.5)TiO3 ceramics modified by Ba2+ cations and overstoichiometric additives (SiO2 and Na2O) was studied. Changes in structure, microstructure, and dielectric parameters were observed depending on solid solutions compositions.

n Erratum to this paper has been published: https://doi.org/10.1134/S0020168521120165

An Erratum to this paper has been published: https://doi.org/10.1134/S0020168521120165