HRTEM analysis on nanocrystalline BaTiO(sub 3) and PbTiO(sub 3): size effects on ferroelectric phase transition temperature

摘要

High-Resolution Transmission Electron Microscopic studies of nanocrystaline particles of BaTiO(sub 3) and PbTiO(sub 3) are reported. There are characteristic differences observed for BaTiO(sub 3) prepared using sol gel (SG) and steric acid gel (SAG) methods. The former exhibit a critical size below which there is no paraelectric/ferroelectric phase transition, whereas BaTiO(sub 3) prepared via the SAG route remained cubic for all conditions. The SAG preparations always showed chemical intergrowth defects whereas the SG preparations were single phase. Atomic resolution images of both varieties showed interesting surface steps and surface relaxations/reconstructions of some facets. Nanocrystalline PbTiO(sub 3) prepared by the SG route remains tetragonal, albeit with decreasing c/a ratio, down to 25nm diameter. HRTEM observations of nanocrystalline PbTiO(sub 3) are also presented. X-ray diffraction, dielectric and Raman scattering measurements also demonstrate pronounced size effects. The relationship between the observed nanostructures and size effects on the physical properties is discussed. 6 refs., 1 tab., 6 figs. (Atomindex citation 28:040305)