Microstructure of Ba1−xLaxTiO3−δ ceramics sintered by spark plasma sintering

Nano-sized Ba1−xLaxTiO3 (0.00 ≤ x ≤ 0.14) powders were prepared by a coprecipitation method and calcined at 850 °C in air. The corresponding ceramics were obtained by Spark Plasma Sintering (SPS) at 1050 °C. These ceramics are oxygen deficient and are marked as Ba1−xLaxTiO3−δ. Both powders and ceramics were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The effect of lanthanum concentration on the densification behavior, on the structure and the microstructure of the oxides was investigated. Average grain sizes are comprised between 54 (3) nm and 27 (2) nm for powders, and 330 (11) nm and 36 (1) nm for ceramics according to the La-doping level. Powders crystallize in the cubic (or pseudo-cubic) perovskite phase. The structure of ceramics consists in a mixture of cubic (or pseudo-cubic) and tetragonal perovskite type phases. As the lanthanum content increases, the tetragonality of the samples decreases, as well as the grain size

Microstructure of single-phase cobalt and manganese oxide spinel Mn3−xCoxO4 ceramics

This paper reports microstructural studies of single-phase Mn3−xCoxO4(0.98 ≤ x ≤ 2.93) spinel ceramics using transmission electron microscopy(TEM) and energy dispersive X-ray spectroscopy (EDX). These ceramics were obtained by conventional sintering or by spark plasma sintering(SPS) of powders prepared by thermal decomposition of coprecipitated oxalate precursors. For x < 1.78 or x ≥ 1.78, the monophasic ceramicscorrespond respectively to quadratic (Q) or cubic (C) spinel structure. The ferroelastic character of the structural phase transition from C to Qis highlighted by specific microstructural features. The effect of chemical composition and heat treatment conditions on the microstructure andessentially on the presence and the characteristics of twins were investigated. The coherent twin interfaces are parallel to (1 1 2) planes in the Qcell. Twins can correspond to: tweeds, single lamellae (widths: 5–306 nm) arranged parallel to each other, large lamellae (widths: 69–928 nm)internally twinned and sometimes arranged in cyclic forms (triangular shapes)

Structural characterization of dense reduced BaTiO3 and Ba0.95La0.05TiO3 nanoceramics showing colossal dielectric values

BaTiO3−x and Ba0.95La0.05TiO3−x nanoceramics showing colossal permittivity values have been characterized. While starting powders are of cubic symmetry, X-ray and Neutron Diffraction techniques and Raman Spectroscopy measurements show that the one-step processed ceramics obtained by Spark Plasma Sintering (SPS) contain cubic and tetragonal phases. Rather large oxygen deficiency determined in such ceramics by Electron Micro Probe analysis and Electron Energy Loss Spectroscopy analyzes is explained by the presence of Ti3+, as evidenced by X-ray Photoelectron Spectroscopy measurements. Transmission Electron Microscopy and High Resolution Transmission Electron Microscopy show that these ceramics contain 50–300 nm grains, which have single-domains, while grain boundaries are of nanometer scale. Colossal permittivity values measured in our dense nanoceramics are explained by a charge hopping mechanism and an interfacial polarization of a large number of polarons generated after sample reduction in SPS apparatus