Finite-size effects in antiferroelectric nanoparticles

We study the size dependence of the antiferroelectric-to-paraelectric phase transition in ultrafine particles of (with x-ray domain size down to ) prepared by the sol - gel method. The phase transition was investigated by means of dielectric and thermal measurements. The nature of the particle size dependence of various properties of antiferroelectric was found to be generally similar to that of typical `displacive' ferroelectrics such as and . In both cases, a size-induced structural distortion towards the high-symmetry paraelectric phase appears to dictate the behaviour of the nanoparticulate system. Nanoparticles of `order - disorder' systems such as behave in a markedly different manner. With decreasing particle size, we observe an increasing deviation of the dielectric response from the Curie - Weiss behaviour. Certain physical situations that may lead to the observed smearing out of the transition in nanoparticles of and are discussed.