Monte Carlo simulations for describing the ferroelectric–relaxor crossover inBaTiO3-based solid solutions

Abstract

The properties induced by the M4 + addition (M = Zr,Sn, Hf) in BaMxTi1 − xO3 solid solutions have been described on the basis of a 2D Ising-like network and Monte Carlo calculations,in which BaMO3 randomly distributed unit cells were considered as being non-ferroelectric.The polarization versus temperature dependences when increasing theM4 + concentration(x) showed a continuous reduction of the remanent polarization and of the criticaltemperature corresponding to the ferroelectric–paraelectric transition and a modificationfrom a first-order to a second-order phase transition with a broad temperature range forwhich the transition takes place, as commonly reported for relaxors. The model alsodescribes the system’s tendency to reduce the polar clusters’ average size whileincreasing their stability in time at higher temperatures above the Curie range,when a ferroelectric–relaxor crossover is induced by increasing the substitution (x). The equilibrium micropolar states during the polarization reversal process while describing theP(E) loops were comparatively monitored for the ferroelectric (x = 0) andrelaxor (x = 0.3) states. Polarization reversal in relaxor compositions proceeds by the growth of several nucleateddomains (the ‘labyrinthine domain pattern’) instead of the large scale domain formationtypical for the ferroelectric state. The spatial and temporal evolution of the polar clusters inBaMxTi1 − xO3 solid solutionsat various x has also been described by the correlation length and correlation time. As expected for theferroelectric–relaxor crossover characterized by a progressive increasing degree of disorder,local fluctuations cause a reducing correlation time when the substitution degree increases,at a given temperature. The correlation time around the Curie temperature increases,reflecting the increasing stability in time of some polar nanoregions in relaxors incomparison with ferroelectrics, which was experimentally proved in various types ofrelaxors.