A. V. Mosunov

Synthesis and Properties of La2(Mo1 – xMx )2O9 (M = Nb, Ta) Ionic Conductors

La2(Mo1 – xMx )2O9 (M = Nb, Ta; 0 < x ≤ 0.2) solid solutions were prepared, and their physicochemical and electrical properties were studied. Second harmonic generation measurements indicate that the solid solutions have a noncentrosymmetric structure and undergo a structural phase transition accompanied by a sharp increase in ionic conductivity, similar to that of La2Mo2O9 . The transition temperature is found to decrease with increasing Nb or Ta content. The introduction of 5 wt % Nb increases the 800°C conductivity of the material.

Spin and Dipole Ordering in Ni2InSbO6 and Ni2ScSbO6 with Corundum-Related Structure

The complex metal oxides Ni2InSbO6 (NISO) and Ni2ScSbO6 (NSSO) have been prepared in form of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties of the compounds were investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. The compounds adopt a trigonal structure, space group R3, of the corundum related Ni3TeO6 (NTO) type. Only one of the octahedral Ni positions (Ni(2)) of the NTO structure was found to be occupied by In (Sc). NTO has non-centrosymmetric structure and is ferroelectric below 1000 K, dielectric and second harmonic measurements suggest that also NISO and NSSO are correspondingly ferroelectric. Magnetization measurements signified antiferromagnetic ordering below TN=60 K (NSSO) and 76 K (NISO). The magnetic structure is formed by two antiferromagnetically coupled incommensurate helices with the spiral axis along the b-axis and propagation vector k = [0, ky,0] with ky= 0.036(1) (NSSO) and ky= 0.029(1) (NISO). The observed structural and magnetic properties of NISO and NSSO are discussed and compared with those of NTO.

Ferroelectric Phase Transitions and Electroconducting Properties of Ceramic BIMEVOX Solid Solutions (Me = La, Zr)

Ceramic solid solutions Bi 4 (V 1−x Zr x ) 2 O 11−z (I), (Bi 1−y La y ) 4 V 2 O 11−z (II) and (Bi 1−y La y ) 4 (V 0.96 Zr 0.05 ) 2 O 11−z (III) with x < 0.30, y < 0.20, were prepared by the solid state reaction method and were investigated by means of various experimental techniques. The low temperature ferroelectric α-phase exists in the solid solutions with x, y ≤ 0.05. The phase transition to paraelectric β-phase was revealed in these compositions by the dielectric spectroscopy, SHG and DTA/DSC methods. Dielectric permittivity measurements confirmed an effect of the domain walls “pinning” due to the presence of oxygen vacancies inherent to the bismuth vanadate based structures. Switching of ferroelectric domains by an external electric field was observed in Piezoresponse Force Microscopy experiments.

Effect of low-melting additives on the structure, phase transitions, and dielectric properties of 0.36BiScO3 · 0.64PbTiO3 ceramics

Ceramic samples of 0.36BiScO3 · 0.64PbTiO3 morphotropic phase boundary solid solutions modified with low-melting additives (bismuth, nickel, and manganese oxides and lithium fluoride; < 5 wt %) have been prepared by solid-state reactions, and the phase formation, microstructure, and dielectric properties of the ceramics have been investigated. The additives were shown to lower the formation temperature of the solid solutions and raise the density of the ceramics. Varying the heat treatment conditions, we obtained single-phase samples, both large-grained, ranging in grain size from a few to tens of microns, and fine-grained, with a submicron-scale microstructure. The ceramics were shown to form through liquid-phase sintering. The additives influenced the dielectric properties, electrical conductivity, Curie temperature, and dielectric relaxation of the ceramics.

Ca10.5 − xPbx(PO4)7 and Ca9.5 − xPbxM(PO4)7 ferroelectrics with the whitlockite structure

We have prepared Ca9.5 − xPbxM(PO4)7 (M = Mg, Zn, Cd) and Ca10.5 − xPbx(PO4)7 solid solutions. A polar whitlockite-like (sp. gr. R3c) crystal structure exists in the range 0 ≤ x ≤ 1.5 for all of the M cations in Ca9.5 − xPbxM(PO4)7 and in the range 0 ≤ x ≤ 2.5 for Ca10.5 − xPbx(PO4)7. X-ray powder diffraction profile analysis results for Ca8.5PbCd(PO4)7 powder demonstrate that the small divalent M cations reside predominantly on the octahedral site M5 of the whitlockite structure, the calcium cation occupy the M1–M3 sites, and the lead cations are located primarily on the M4 site. Differential scanning calorimetry, second-harmonic generation, and dielectric permittivity data indicate that all of the synthesized phosphates are high-temperature ferroelectrics. The highest Curie temperatures are offered by the x = 0.5 materials, in which most of the lead resides in the spacious oxygen polyhedra M4 and only a small amount of lead is incorporated into the smaller polyhedra around M1–M3. The nonlinear optical activity has a maximum in the middle of the solid-solution series and is an order of magnitude higher than that of the parent, lead-free phases.

Phase Transitions, Dielectric and Piezoelectric Properties of BiScO3-PbTiO3 Ceramic Solid Solutions

Dielectric and piezoelectric properties of ceramic solid solutions based on the compositions close to the MPB in the system (1-x)BiScO3 – xPbTiO3 (x- 0.63, 0.635, 0.64) have been studied. The 1st order phase transitions were observed at temperatures near 700 K. Increase in the lead titanate content stimulates slight increase in the TC value. Cr2O3 additives in amounts up to 0.2 w. % favor to the decrease of total conductivity and dielectric loss at high temperatures. Increase in the d33 and kt piezocoefficients was observed in modifed ceramic. Besides peaks in temperature dependences of dielectric permittivity and dielectric loss marked ferroelectric to paraelectric phase transitions, effects of dielectric relaxation, determined by oxygen vacancies were revealed.

Phase transitions and the dielectric and piezoelectric properties of ceramic solid solutions based on BiScO3-PbTiO3

The ferroelectric and piezoelectric properties of ceramic solid solutions having a composition of (1−x)(Bi0.9Nd0.1)(Sc0.9B0.1)O3 − xPbTiO3 (x = 0.60–0.66; B = Lu, Yb, Er, Y) and obtained by solid state reaction were studied. An increase in the Curie temperature was found upon an increase in the concentration of lead titanate, while a drop occured upon the doping of the A and B sublattices. It was shown that at high temperatures, MnO2 and Bi2O3 additives lead to a reduction in the total conductivity and a dielectric loss of less than one order of magnitude. In modified ceramics, an increase in the d33 and kt piezoelectric coefficients was observed as well. The effects of dielectric relaxation that are determined by the composition of the ceramics were revealed.

Preparation and Properties of Oxygen-Selective LaGaO3-Based Ceramics with Mixed Ionic–Electronic Conduction

A continuous series of (La0.9Sr0.1)[(Ga1 – xFex)0.8Mg0.2]O3 – δ perovskite solid solutions (x = 0–1) were prepared by ceramic processing techniques. X-ray diffraction, dilatometry, thermogravimetry, and dielectric spectroscopy data indicate that increasing the Fe content of the solid solutions leads to a change from oxygen ionic to ionic–electronic conduction.

Synthesis, Structure, Microstructure, and Electrical Conductivity of (La,Sr)(Ga,Mg)O3 – δOxide-Ion-Conducting Ceramics

Oxide-ion-conducting perovskite ceramics (La1 – ySry)(Ga1 – xMgx )O3 – δwere prepared using hydrated Mg and La salts as starting reagents. X-ray diffraction and IR spectroscopy data demonstrate that the symmetry of the solid solutions changes in the sequence orthorhombic–rhombohedral–cubic with increasing Sr + Mg content.

Ferroelectricity in the KTiOPO4 family

Abstract The main physical characteristics of potassium titanyl phosphate-type ferroelectrics AMOXO4 are related to crystal structure parameters such as the basic and interstitial positions of the A atoms and the MO6 octahedra distortions. On these grounds, a new understanding of the structural origins of the high ionic conductivity in silicates and germanates of the KTiOPO4 family is reached. The optical nonlinearity and Tc behaviour in solid solutions with niobium starting from KSbOGeO4 and KTaOGeO4 is also discussed.