Effect of Internal Stress on Physical Temperature Characteristics of Cerium‐Doped and Gadolinium‐Doped Barium Titanate Ceramics

Abstract

The effect of internal stress on the physical properties (the temperature dependence of the dielectric constant and the lattice constant, and the diffuseness (␥)) of solid solutions of 0.97BaTiO 3 -0.03Gd 2 O 3 :1.5TiO 2 and 0.97BaTiO 3 -0.03CeO 2 :1.5TiO 2 was investigated using various particle sizes of the starting BaTiO 3 , pressure-dielectric spectroscopy, and high-pressure X-ray analysis. The grain size was almost proportional to the particle size of the starting BaTiO 3 and was inversely proportional to the internal stress. A sudden change in internal stress occurred at grain sizes of ∼2 µm for cerium-doped BaTiO 3 and ∼3 µm for gadolinium-doped BaTiO 3 . With an increase in external pressure and a decrease in grain size, the lattice anomalies of the cubic-to-tetragonal transformation and two other factors (the tetragonal-to-orthorhombic and orthorhombic-torhombohedral transformations) shifted to lower and higher temperatures, respectively. The temperature dependencies of the dielectric constant and the lattice constant were less sensitive to external pressure in cerium-doped core-shellgrained BaTiO 3 than in gadolinium-doped homogeneousgrained BaTiO 3 ; this difference was attributable to internal stress. In cerium-doped BaTiO 3 , ␥ was related to internal stress.

High‐Permittivity Double Rare‐Earth‐Doped Barium Titanate Ceramics with Diffuse Phase Transition

“…14(a) were in the process of aggregation, and the boundaries with fine grains gradually became vague. Generally speaking, when highly pure BaTiO 3 powder is used as a raw material and the mixture is sintered at a lower temperature (≤1400°C) for a shorter time (≤2 h), the Ce‐doping effect on the BaTiO 3 microstructure 13,64 is similar to Zr doping 50,65 . This is prone to cause chemical inhomogeneity, such as core‐shell‐structured grains with an unreacted tetragonal ferroelectric BaTiO 3 core, non‐ferroelectric‐modified shells, and gradent regions with varying dopant concentrations.…”

“…However, the Curie peak decreases to ɛ′∼3000 at 1 kHz as it moves to room temperature 3–6 . In addition to La substitution at Ba sites, other larger rare‐earth ions acting as donors, such as Nd, 7,8 Sm, 9,10 Eu, 11 and Gd 12,13 (with slight amphoteric behavior), 14,15 does not seem to be as efficient as La dopant in raising permittivity. For intermediate rare‐earth ions, such as Dy, Ho, and Er, that show an amphoteric site‐occupation preference for both A/B sites by the self‐compensation mode, 15–18 or smaller rare‐earth ions such as Yb or Lu, 19,20 that prefer to occupy B sites (acting as acceptors at Ti sites), the Curie peak shift towards room temperature in doped BaTiO 3 ceramics (such as with Dy 21,22 and Er 23 dopants) is limited because of lower solid solubility at Ti sites of the BaTiO 3 lattice 22,24–26 as compared with Ce, 27 although occupation at Ti sites usually leads to relaxor‐type ferroelectric behavior and the dielectric peak decreases with increased dopant 23 .…”

Mutual Solid Solubility and Phase Equilibrium in the System BaTiO3–BaCeO3

“…Ce-doped BaTiO 3 ceramics have been extensively studied owing to their interesting dielectric properties associated with their valence state change. [1][2][3][4][5][6][7][8][9][10] Ce can be incorporated into the Ba site as Ce 3þ (4f 1 ), leading to the first-and secondorder phase transitions with high-k sharp-peak behavior (" 0 m > 10000); 1,4) or into the Ti site as Ce 4þ (4f 0 ), leading to diffuse phase transition (DPT) with a lower room-temperature dielectric permittivity (" 0 RT < 3000). 7) For the solid solution formation of Ba(Ti 1Àx Ce x )O 3 , the rather large difference in ionic radius between Ce 4þ (0.87 A) 11) and Ti 4þ (0.605 A) 11) leads to incomplete solid solubility.…”

The Preparation of Barium Stannate Titanate Ceramics via Solid State Reaction Method

“…Barium titanate, BaTiO 3 (BT) is a typical ferroelectric material with a perovskite structure [1]. BT is known as a typical ferroelectric material with Curie temperature (T c ) around 120 o C. BT and has been widely used for condensers, filters, oscillators and so on, due to its ferroelectric, pyroelectric and optoelectric properties [2]. Barium stannate titanate, Ba(Sn x Ti 1-x )O 3 (BST) is obtained by substituting ions at the Ti-site of BaTiO 3 with Sn ions.…”