Eriks Klotins

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.

Modeling of trapped charge effects in ferroelectrics: application to piezoactuators

The strain response of lead zirconate titanate piezoelectric multilayer actuators have been measured up to 107 N/m2 stress and the 3.106 V/m periodic unipolar driving voltage. An additional nonstationary strain component is detected. This effect is explained in terms of a simple solution of polarization kinetics specific for unipolar driving voltage. Preliminary experimentally assertions are given for space charge effects which manifest itself in the strain as well as charge plot after removing the mechanical load. It demonstrates that the static load free equilibrium of the actuator is not complete and the charge recently supported by the piezo voltage and then trapped forms a nonuniform space charge field confining the strain relaxation.

Numerical Evidences of Polarization Switching in PMN Type Relaxor Ferroelectrics

We present a conceptual and computational framework for chemically ordered Pb(Mg 1/3 Nb 2/3 O 3) (PMN) type supercells violating disorder of the host lattice. The effective Hamiltonian is specified by invariance under permutations of supercells and by the dipole-dipole interaction supporting both local nonzero and zero mean polarization of the structure. Statistics treated in canonical ensemble within the mean field approach reveals emergence of polar nanoregions as supported by interplay between the (random) initial state polarization of supercells and their interactions increased at cooling.

Polar nanoregions in Pb(Mg1/3Nb2/3)O3 (PMN): insights from a supercell approach

We report construction of a model of polar nanoregions in the PMN relaxor ferroelectric based on first-principles lattice dynamics for chemically ordered supercells [S.A. Prosandeev et al., Phys. Rev. B 70, 134110 (2004)], combined with invariance under permutations and dipole-dipole interaction as a source supporting randomly oriented residual polarization. Representative analytical estimates of polar nanore-gion — supercell mapping reproduce both nonzero local and zero macroscopic polarization of the structure, as well as the temperature change of the supercell anisotropy at cooling and field cooling.

Mesoscopic Scale Structural Instability in Ferroelectrics

First-principles statistics addressed to structural phase transitions and temperature development of ferroelectric response is derived within the framework of the Fokker-Planck (Smoluchowsky) equation as complementary to the Monte Carlo [R.D King-Smith., D Vanderbilt, Phys. Rev. B 49, 5828–5844 (1994)] and molecular dynamics [T. Nishimatsu, U. V Waghmare, Y. Kawazoe., D. Vanderbilt, arXiv:0804.1853v2] simulations. Illustrative example of is given for 5 × 5 × 5 BaTiO 3 supercell.

Stochastic Dynamics of Ferroelectric Polarization

This study is addressed to the conceptual and technical problems emerging for ferroelectric systems out of thermodynamic equilibrium. The theoretical setup includes a lattice of interacting cells, each cell obeying regular dynamics determined by Ginzburg-Landau model Hamiltonians whereas relaxation toward minimum energy state is reproduced by thermal environment. Representative examples include polarization response of a single lattice cell, birth of a domain as triggered by the ergodicity breaking, and the effect of nonlocal electroelastic interaction all evidenced combining the Fokker-Planck, imaginary time Schrödinger and symplectic integration techniques.

Notes on the Electroelastic Interaction in Joint Hamiltonian and Stochastic Treatment of Polarization Response

Conventional Landau theory for ferroelectric phase instability is extended by entities accounting for the violation of thermodynamic equilibrium and the impact of thermal fluctuations. The physical content concerns Ginzburg-Landau type model Hamiltonians assigned to the mean field interaction of macroscopically small and microscopically large lattice cells affected by thermal fluctuations. A special topic derived in a systematic way is long range electroelastic interaction formally given by selfconsistent solution of the polarization and strain fields. Test solution for inhomogeneous strain in a slab is presented within the framework of lattice cell picture.

High Field Polarization Response in Ferroelectrics: Current Solutions and Challenges

Polarization response including ergodicity breaking and the divergence of relaxation time is reproduced for model Hamiltonians of growing complexity. Systematic derivation of the dynamical equations and its solutions is based on the Fokker-Planck and imaginary time Schrödinger equation techniques with subsequent symplectic integration. Test solutions are addressed to finite size and spatially extended problems with microscopically interpretation of the model parameters as a challenge.

The strain response of piezoelectric multilayer actuators under combined action of electric field and in-plane uniform load

Abstract The driving field governed strain of lead zirconate titanate piezoelectric multilayer actuators have been made within the 107 N/m2 stress and the 3 · 106 V/m triangle-like upward-down-ward driving voltage. A slow strain component as well as a specific relaxation pattern are detected being additional to the periodic part and attributed to the trapped space charge effects favored by nonuniform electric field of the multilayer.