Qilin Gu

Rod-like NaNbO3: mechanisms for stable solvothermal synthesis, temperature-mediated phase transitions and morphological evolution

One dimensional (1D) NaNbO3 powders have attracted increasing attention for their excellent photo-catalytic and piezoelectric properties, and the stable, moderate and low-energy synthesis of the targets is highly desirable. Herein, a facial solvothermal strategy is adapted to synthesize the one-dimensional (1D) rod-like precursors Na7(H3O)Nb6O19·14H2O by using isopropanol as the reaction medium. When the precursor is subjected to post-heating treatments, rod-like orthorhombic as well as approximate ellipsoid-like monoclinic NaNbO3 powders are obtained. Corresponding mechanisms for the stable solvothermal synthesis, morphological evolution and phase transition are further proposed and discussed.

Sol-hydrothermal synthesis, crystal structures and excellent dielectric stability of yttrium doped BaTiO3 ceramics

Monodisperse Yttrium-doped BaTiO3 (YBT) nanoparticles with good crystallinity and uniform size distribution have been synthesised via a modified sol-hydrothermal method. The solubility of yttrium in BT was no more than 1 mol%. However, at higher Y3+ content, excess Y3+ were inclined to form Y(OH)3 impurities, and after high temperature sintering, impurity YBa3Ti2O8.5 can be detected in the ceramics. Further, the variation in the crystal volume indicated that Y3+ preferred to substitute for Ti4+ as an acceptor. FE-SEM images revealed that the grain size of the ceramics gradually decreased with the raising Y3+ concentration. Notably, YBT ceramics with 3 mol% Y3+ presented outstanding dielectric-temperature stability, benefitting from the diffuse ferroelectric–paraelectric phase transition and the existence of YBa3Ti2O8.5 phases. Stable dielectric-temperature property and low dielectric loss of the YBT ceramics doping with 3 mol% Y3+ in the range from 1 kHz to 1 MHz render it as a promising candidate material for high frequency application.

Annealing temperature effects on the electrical properties of (K, Na) NbO3 thin film fabricated by a sol-gel process with a citrate precursor solution

ABSTRACT Utilizing the comparatively low cost niobium pentoxide (Nb2O5) as raw material, (K,Na)NbO3(KNN) thin films were deposited onto Ti substrate by a sol–gel non-alkoxide process. The effects of annealing temperature on the phase, morphology, dielectric, and ferroelectric properties of KNN thin films were investigated. KNN thin films without impurities were obtained above 700°C, and the microstructure of all films were dense and uniform. A maximum dielectric constant of 480 was obtained in the film annealed at 700°C, which is comparable to the film prepared from niobium ethoxide.