Effect of heating modes on reactive sintering of Ca3Co4O9 ceramics

Abstract

The traditional solid-state reaction method was employed to synthesize bulk calcium cobaltite (Ca349/Ca3Co4O9) ceramics via ball milling the precursor mixture. The samples were compacted using conventional sintering (CS) and spark plasma sintering (SPS) at 850, 900, and 950◦C. The X-ray diffraction (XRD) pattern indicates the presence of the Ca349 phase for samples sintered at 850 and 900◦C. In addition, SPS fosters higher densification (81.18%) than conventional sintering (50.76%) at elevated sintering temperatures. The thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) performed on the precursor mixture reported a weight loss of ~25.23% at a temperature range of 600–820◦C. This current work aims to analyze the electrical properties (Seebeck coefficient (s), electrical resistivity (ϱ), and power factor) of sintered samples as a function of temperature (35–500◦C). It demonstrates that the change in sintering temperature (conventional sintering) did not evince any significant change in the Seebeck coefficient (113–142 µV/K). However, it reported a low resistivity of 153–132 µΩ-m and a better power factor (82–146.4 µW/mK2) at 900◦C. On the contrary, the SPS sintered samples recorded a higher Seebeck coefficient of 121–181 µV/K at 900◦C. Correspondingly, the samples sintered at 950◦C delineated a low resistivity of 145–158 µΩ-m and a better power factor (97–152 µW/mK2).