Thermal Change in Hot-Pressing TiSe_1.6 and TiSe_1.5

Abstract

Thermal changes in hot-pressed TiSe_1.6 and TiSe_1.5 are investigated in an argon atmosphere up to 1500°C. X-ray powder diffraction analysis of synthesized TiSe_1.6 showed mixed diffraction patterns of hexagonal type TiSe_1.6 and monoclinic type Ti₅Se₈. Ti₅Se₈ disappeared after hot-pressing at 500°-600°C. Above this temperature range, only hexagonal phase was found. TiSe_1.6 releases some Se atoms and Se/Ti ratio decreases by hot-pressing above 1300°C. Hot-pressing at 1500°C gives an Se/Ti ratio approximately equal to 1.5. As reported in our previous paper, synthesized TiSe_1.5 is hexagonal. The X-ray diffraction pattern of TiSe_1.5 is similar to that of hexagonal type TiSe_1.6 except some small diffraction peaks which might be of superstructures. The lattice parameters of TiSe_1.5 are slightly different from those of hexagonal TiSe_1.6. TiSe_1.5 is stable up to 1500°C. Progressive densification and grain growth in TiSe_1.6 start at relatively low temperatures. In TiSe_1.5, densification and grain growth proceed at rather higher temperature range. These differences in sintering behavior between TiSe_1.6 and TiS_1.5 is ascribed to the difference in the stability of crystal phase and to the Ti concentration in partially Ti occupied layers of these phases. Sintered bodies with the highest compressive-strength and high density are obtained by hot-pressing TiSe_1.5 at 1400°C.