Effect of Particle Size on the Room‐Temperature Crystal Structure of Barium Titanate

Abstract

The room-temperature tetragonal-to-cubic transformation in BaTiO, powders with decreasing particle size has been carefully studied, using materials prepared mainly by hydrothermal methods. Hydrothermal BaTiO, powders exhibited a more uniform particle size distribution than oxalate-route powders, with X-ray diffraction and electron microscopy indicating that powders 50.19 pm in size were fully cubic while powders 20.27 pm were completely tetragonal (within a 5% detection limit for cubic material) at room temperature. The tetragonal-to-cubic transformation temperature was also found to lie in the range of 121" -C 3°C for BaTiO, powders with room-temperature (c/a) values > 1.008. No transformation could be detected using differential scanning calorimetry for BaTiO, particles with a (cla) c 1.008 at room temperature. BaTiO, powder with a particle size just too small (0.19 pm) to be tetragonal at room temperature remained cubic down to 80 K. Different models for the cubic-to-tetragonal room-temperature transformation are discussed. Hydroxyl ions do not appear to greatly affect the cubic-to-tetragonal transformation, which appears to be essentially dependent on particle size. It is concluded that a model based on surface free energy, as previously discussed for the monoclinic-to-tetragonal transformation at room temperature of fine ZrO, particles, is consistent with the experimental data.

Effect of Internal Electric Fields on Charge Carrier Dynamics in a Ferroelectric Material for Solar Energy Conversion

“…The suppression of ferroelectric behavior in BaTiO 3 nanoparticles is well documented in the literature. [ 9,[26][27][28][29] The TF-BaTiO 3 fi lms studied herein are in the cubic phase and are therefore non-ferroelectric at room temperature (see X-ray diffraction data in Figure S1 in the Supporting Information). Transient absorption measurements were obtained on the μs-s timescale using band-gap excitation at 355 nm (≈150 μJ cm −2 , 0.33 Hz, Ar atmosphere), a wavelength at which both samples exhibited strong light absorption (we estimate that the absorption depth will be shorter than the width of the surface band bending, see Figure S2 in the Supporting Information), and probed in the range 460-950 nm.…”

Effect of Barium Titanate Seed Particles on the Sintering and Lattice Parameters in PbMg1/3Nb2/3O3 Ceramics

“…X-ray diffractometry of the BT seed particles indicated a cubic crystal structure at room temperature, which is consistent with the literature reports that the cubic-tetragonal ferroic transition in BT is inhibited in the nanometric size range. 19 Particle-size distribution by sedimentation process was a narrow distribution with a mean particle size of 0.6 m (Fig. 1), and transmission electron microscopy (TEM) of the BT seeds (Fig.…”

Structure and Composition of Ba-W-Ti-O Ceramics Interface Regions Formed at Ultrasonic Vibration

“…The physical characteristics of barium-titanate ceramics were shown to be size dependent [1][2][3][4], and the Ba/Ti ratio was found to determine the grain growth mechanism [5,6]. At the same time, as was shown in [7][8][9], the relation between the elements in the ceramic interface regions may substantially differ from that in the bulk, which can result in both phase transformation and new phase formation.…”