L. Shebanovs

Electrocaloric Effect in Some Perovskite Ferroelectric Ceramics and Multilayer Capacitors

Electrocaloric effect (ECE) of pure and modified PbSc 1/2 Ta 1/2 O 3 (PST) and its solid solutions and PbMg 1/3 Nb 2/3 O 3 - PbTiO 3 ferroelectric ceramics is studied at different temperatures and external electric field intensities. High value of (ECE) up to 2.3 K is observed in PST ceramics at modification in B sublattice by Co 3+ and Sb 5+ ions. The features of ECE in PST are explained by significant structure rearrangement at electric field induced Fm3m M R3m phase transition and high long range ordering of B ions in the ABO 3 perovskite structure. A further increase of ECE is observed in ceramic multilayer capacitors at higher electric field intensities up to 138 kV/cm.

Structure and properties of hot-pressed Pb(Lu1/2Nb1/2)O3-PbTiO3 binary system ceramics

Solid solution series of the (1 - x)Pb(Lu1/2Nb1/2)O3 - x PbTiO3 binary system ceramics (PLuNT) were synthesized and hot-pressed (temperature 950°C to 1130°C, pressure 25 MPa); its structure, dielectric and piezoelectric properties were studied. Pure lutecium niobate PLuN (x = 0) has a pronounced long-range order in the B-sublattice and an antiferroelectric to paraelectric phase transition at ∼258°C. The phase structure of the PLuNT system, at room temperature, changes from a pseudomonoclinic (psd-M, space group Bmm2) to tetragonal (T, space group P4mm). The pseudomonoclinic phase extends over the 0 ≤ x ≤ 0.38 interval within which the monoclinic angle β proceeds a minimum near to 90° at x ≅ 0.2. The morphotropic region covers the interval x = 0.38 - 0.49, the concentration ratio psd-M:T≅ 1 (the morphotropic phase boundary—MPB) corresponds to x = 0.41. Within the morphotropic region, a rather strong distortion of the unit cell—(c/a - 1)≥ 0.02, β ≥ 90.37º, characteristic of “hard” piezoelectrics is maintained. Dielectric dispersion and broadening of the phase transition, features typical to relaxors, are observed within the concentration interval of 0.1 ≤ x ≤ 0.3. The highest electromechanical coupling coefficients: kp = 0.66, kt = 0.48, k31 = 0.34 of (1 - x) PLuN−xPT ceramics are attained in compositions near the MPB at x ≈ 0.41. Non-isovalent doping of PLuNT with La3+ in Pb sublattice shifts the MPB to lower values of x.

Effects of structure ordering, structure defects and external conditions on properties of complex ferroelectric perovskites

Abstract Structural rearrangements in lead-containing (A‘A’) (B’B“)O3 type perovskite compounds are caused by technological treatment, high-energy radiation and ambient conditions. Variation of structure ordering along with modification (substituted or defected solid solutions) may provide promising compositions for applications, e.g., cascade microcryogenic devices (PST solid solutions); efficient piezoelectric materials – here the new (1 – x)Pb(Lu1/2Nb1/2)O3 – xPbTiO3 system in the morphotropic region. The maximum values of the electromechanical coupling coefficients kp = 0·663, kt = 0·481, k 31 = 0·355 were attained in compositions PLuNT 59/41 (Tm = 353°C) near the morphotropic phase boundary. In P(L)ZT and PLT thin films asymmetry of piezoelectric coefficient d 33 hysteresis diminished values of d 33 and their frequency dependence were attributed to residual stress at the film-substrate/electrode interfaces and unrelaxed strain characteristic in highly oriented thin films. Neutron irradiation by fluen...

Radiation effects on lead-containing perovskite ceramics

Abstract Optical spectra and dielectric parameters are used to study PLZT X/65/35 (X=4.5−11 at.% La) and PSN ceramics subject to gamma- electron-, and neutron irradiation. In neutron-irradiated ceramics stable defects, maintained at annealing up to 700 °C are manifested by a gradual shift of extinction edge near the fundamental absorption to longer wavelengths and by reduced polarization values. The thermal dependence of the extinction edge in reference samples of PLZT and PSN has been determined to be ca. 0.10 nm/deg (0.9 meV/deg) and 0.125 nm/deg, respectively in the range 20-500°C. In PLZT 6.5-8/65/35 ceramics a defect enforced phase transformation from the initial rhombohedral structure to “quasicubic” with essential broadening of the phase transition takes place.

Thermodynamic properties at the phase transition of Pb(Zr, Sn, Ti)O3 solid solutions

Abstract Field induced deformation and electrocaloric effect are investigated in the vicinity of phase transition at 163°C. The sharp increase of electrostriction below Tc is explained by the field induced ferroelectric to antiferroelectric phase transition. The antiferroelectric phase appears and remains stable below Tc in the absence of field. Elastic compliance and thermal expansion as functions of temperature are studied.

Isomorphous ion substitutions and order-disorder phenomena in highly electrocaloric lead-scandium tantalate solid solutions

Abstract The authors discuss the physical background of the electrocaloric effect in PST ceramics and its solid solutions. The most important contribution to the electrocaloric effect is due to field-induced Fm3m→R3m phase transition in the case of high long range ordering degree of B-ions in the perovskite structure ABO3.

PHASE TRANSITIONS AND PROPERTIES OF PEROVSKITE FERROELECTRIC CERAMICS AND FILMS FOR CERTAIN APPLICATIONS

Abstract The structure-properties relationships and phase transitions in perovskite ceramics, and films of PLZT, PLZST, PST, PSN, PMNT compounds are discussed with regard to ordering, relaxor behaviour, pronounced ferroelectric, electromechanical and electrocaloric properties. The theoretical approach is extended to the time dependent Ginsburg-Landau model. The evolution of dielectric properties in relaxors after the change of temperature and electric field creating an increase of dielectric permittivity is found to follow a logarithmic law of decay. A strong electromechanical response is observed in a number of thin films of different compositions.

Effect of compressive stress on dielectric and ferroelectric properties of 0.25PSN-0.75PLuN ceramics

The PSN-PLuN solid solutions have been prepared in the whole composition range for the first time. The dielectric, pyroelectric and hysteresis loops measurements of the 0.25PSN-0.75PLuN ceramics stress-free or under the stress (0-1.5 kbar) have been carried out. It is found that compressive stress shifts the phase transformation and decrease the field-polarization hysteresis. These effects can be mainly connected with the change in domain walls dynamics and with polarization switching under the action of stress.

New ferroelectric materials on the basis of PbSc1/2Nb1/2O3–PbLu1/2Nb1/2O3 solid solutions

Abstract Original binary solid solutions PbSc 1/2 Nb 1/2 O 3 –PbLu 1/2 Nb 1/2 O 3 (PSN-PLuN) have been produced. First of all nominally pure PSN and PLuN were synthesized by solid state reaction from oxides and carbonates. These compounds were mixed in different proportions to obtain (1− x )PSN− x PLuN solid solutions. Ceramic samples were hot-pressed at gradual change of the temperature. Solid solutions have the perovskite structure and are completely soluble in each other. Differential thermal analysis and X-ray diffraction were used to examine the synthesis and phase constitution. Dielectric properties—dielectric permittivity e and dielectric loss tan δ of ceramic samples of originally synthesized PbSc 1/2 Nb 1/2 O 3 –PbLu 1/2 Nb 1/2 O 3 (PSN−PLuN) solid solution series were measured as functions of temperature. In (1− x )PSN− x PLuN solid solutions the phase transition temperature drops at small values x further proceeding through a minimum.

CO2 laser-induced structure changes in lead zirconate titanate Pb(Zr0.58Ti0.42)O3 sol–gel films

Based on absorption spectra of lanthanum modified lead zirconate titanate Pb0.9La0.1(Zr0.65Ti0.35)O3 (PLZT10/65/35) ferroelectric ceramics an idea of local and selective treatment of lead zirconite titanate Pb(ZrXTi1−X)O3 (PZT) sol–gel film in the multi-layer structure by CO2 laser radiation was formulated. The possibility to obtain PZT perovskite film on the SiO2/Si substrate by irradiation with CO2 laser was shown experimentally. X-ray studies revealed the PZT perovskite structure ratio growth at the expenses of pirochlore structure with an increased power density of laser radiation.