Three theoretical studies of ferroelectric materials in different geometries

Abstract

OF THE DISSERTATION Three Theoretical Studies of Ferroelectric Materials in Different Geometries By LUCIA PALOVA Dissertation Director: Professor Premala Chandra Using a combination of numerical and analytical techniques, I present characterizations of ferroelectric materials in bulk, thin-film and nanostructure geometries. My results have impact on ongoing research and on design for nanodevices. Size-dependent effects in ferroelectrics are important due to their long-range electrostatic interactions; thus their dielectric properties depend on electromechanical boundary conditions. In my first study, I address the effects of strain on the measured properties of thin-film (TF) ferroelectrics. It has been suggested that the observed suppression of many TF dielectric characteristics implies underlying strain gradients in the film. I show that the same effects can be explained by a simpler model with homogeneous strain, and I suggest a “smoking gun” benchtop probe. The quantum paraelectric-ferroelectric transition (QPFT) is the topic of my second study. Using methods including finite-size scaling and self-consistent Gaussian theory, I calculate the classicalquantum crossover in the dielectric susceptbility and the resulting temperature-pressure phase diagram; comparison with current experiment is excellent and predictions are made for future measurements. Here, temperature can be considered a “finite-size effet” in time, and previous results on the QPFT using diagrammatic techniques are recovered and extended using this approach. Recent synthesis of artificially structured oxides with “checkerboard” patterning at the nanoscale