The influence of spark plasma sintering temperature on the properties of Sb-doped barium stannate ceramics

Abstract

Barium-stannate (BaSnO3, BSO) is a member of the perovskite-type alkaline earth stannates ASnO3 (A = Ca, Sr, Ba) with an ideal cubic crystal structure (space group: ). Doping with antimony (Sb5+) can change this wide band-gap semiconductor (Eg = 3.1-3.4 eV) into an n-type semiconductor with high electrical conductivity at room temperature. The major drawbacks in the BSO-based ceramics synthesis are phase composition and low density of final ceramic materials. These problems could be solved using spark plasma sintering (SPS), a current and pressure-assisted technique, which enables the preparation of dense ceramics at significantly lower temperatures and for a shorter time. To investigate the influence of spark plasma sintering temperature on the structural, microstructural and electrical properties of BaSn1-xSbxO3 (BSSO, x = 0.00; 0,04; 0.06; 0.08; and 0.10) ceramics samples, BSSO powders were spark plasma sintered at 1100 °C, 1200 °C and 1250 °C for 5 min. X-ray diffraction (XRD) analysis confirmed that all ceramic samples sintered at 1100 °C crystallized in a single-phased cubic BSO structure. Their relative densities were in the range of 72–82% ρt. Sintering at 1200 °C increased the samples’ relative densities to 79–96% ρt, but also induced the formation of a barium-rich secondary phase, Ba2SnO4. Rising the sintering temperature further to 1250 °C induced the melting of all samples except BaSn0.92Sb0.08O3. Field emission scanning electron microscopy (FE-SEM) revealed that doping with antimony decreased the grain sizes in BSSO samples sintered at 1100 °C and 1200 °C up to the concentration x = 0.08. Electrical measurements revealed the typical semiconductor behavior of the undoped samples, showing nonlinear current-voltage characteristic and the existence of one semicircle in their impedance spectra, characteristic for materials with double Schottky barrier at the grain boundaries. However, samples with higher dopant concentrations (x = 0.08 and 0.10) showed significantly lower electrical resistivity and linear current-voltage characteristic. The lowest and almost constant value of electrical resistivity in the temperature range of 25–150 °C, and complete loss of the semicircle in its impedance spectrum revealed the metallic-like behavior of sample BaSn0.92Sb0.08O3 sintered at 1200 °C.