E. Birks

PHASE TRANSITIONS IN Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 SOLID SOLUTIONS

ABSTRACT Studies of nature of polarization in ternary solid solutions of Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 were done, using measurements of dielectric properties and polarization hysteresis loops. Various stages of relaxor behavior depending on concentration of PbTiO3 were established and compared with other known ferroelectric relaxors.

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.

Phase Transitions in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 Solid Solutions

All sequential steps of transfer from relaxor to normal ferroelectric phase transition are found in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 if concentration of PbTiO3 increases. The relaxor properties in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 solid solutions are described by the power law and Vogel-Fulcher relationship. Concentration dependence of the relevant parameters is discussed. Stability of relaxor and ferroelectric phases is discussed by analyzing behaviour of critical electric fields.

Electrocaloric effect in PLZT ceramics

The electrocaloric effect in rhombohedral PLZT ceramics is studied as function of applied field and temperature. The results obtained are consistent with the general idea of the existence of an intermediate state of mixed polar and nonpolar regions in the interval of the diffuse phase transition. The step-like change of the temperature at the field-induced first-order phase transition in the temperature range close to Tt corresponds to an entropy jump of 0.18 × 10-2 J/cm3 · deg.

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.

Structure and Dielectric Properties of Na1/2Bi1/2TiO3-BaTiO3 Solid Solutions

Dielectric properties, polarization and x-ray diffraction are studied for (1-x)Na_1/2Bi_1/2TiO₃-xBaTiO₃ solid solutions in a concentration range above the morphotropic phase boundary. It is showed that all the studied compositions have tetragonal structure with maximal tetragonality slightly above the morphotropic phase boundary. Ferroelectric relaxor behavior is observed in a wide concentration range of BaTiO₃. Stability of the relaxor state decreases with increasing BaTiO₃ concentration, but only for compositions with low Na_1/2Bi_1/2TiO₃ content the normal ferroelectric-paraelectric phase transition, which is characteristic to pure BaTiO₃, occurs. Mechanisms, which influence the change of the phase transition character and promote the appearance of the relaxor state, are discussed. The phase diagram of (1-x)Na_1/2Bi_1/2TiO₃-xBaTiO₃ is revised.

Phase transitions of Pb0.99Nb0.02(Zr0.75Sn0.20Ti0.05)O3ceramics

Abstract The dielectric, elastic and electromechanical properties, electrocaloric effect and thermal expansion of poled and depoled Pb0.99Nb0.02(Zr0.75Sn0.20Ti0.05)O3 samples are presented to evaluate the nature of polar phases existing in the solid solution above room temperature. The Kittels free energy expansion is used to explain some essential features of physical properties.

Radiation damage of PLZT and PSN ceramics

Abstract Selected optical (absorption coefficient), dielectric (polarization) and electrooptical (quadratic electrooptical coefficient) parameters of PLZT X/65/35 and PSN ceramics exposed to various radiation environments (γ-rays, electrons, neutrons) have been studied. The observed property changes depend on the type of radiation, the dose and, in the case of the dielectric properties, on the state of sample polarization. Special features observed upon annealing the irradiated samples are discussed.