Ca_<i>x</i>Ba_1–<i>x</i>Nb₂O₆ Ferroelectric Nanopowders for Ultrahigh-Density Optical Data Storage

Abstract

In the present work, structural studies have been carried out on new nanosized calcium barium niobate (CaxBa1–xNb2O6, CBN) ceramic nanopowders synthesized by an aqueous organic gel route at a relatively low calcination temperature of 800 °C. Homogeneous Ca–Ba–Nb precursor gels were prepared using the starting materials Ca-EDTA, Ba-EDTA, and niobium citrate complex from which precursor powders were obtained after prolonged heating at 80 °C. The phases, nanostructures, local structures, microstructures, and morphological analysis of the CaxBa1–xNb2O6 (x = 0.25, 0.35, and 0.50) nanopowders were studied by X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Raman and IR spectroscopy. The powder X-ray and electron diffraction patterns show the formation of a nearly single-crystalline phase of CBN powders with a partially occupied tungsten bronze (TB)-type structure in tetragonal symmetry. The precursor gels calcined in the temperature range 800–900 °C generated nanopowders with an average particle size of 30–50 nm. The crystallite size and average particle size confirmed and calculated from X-ray broadening and transmission microscopes were 20 and 30–50 nm, respectively, for all samples. The impacts of the compositions and crystallite sizes on the structural properties of the CBN nanopowders are discussed based on the Raman scattering results. The microstructure and compositional homogeneity were investigated by SEM and TEM, which confirmed the fine-grained almost homogeneous agglomerate nanostructure of synthesized ceramics. Furthermore, the electronic and optical properties of Ca0.25Ba0.75Nb2O6 were predicted by first-principles calculations based on density functional theory from the CASTEP code as well. Analysis of the various optical properties, especially the photorefractive effect, suggests that CBN can be potentially applied for ultrahigh-density optical data storage.