The phase evolution mechanism in Fe(Se, Te) system

Highlights: • The phase evolution mechanism in Fe(Se, Te) system was synthesis investigated. • Atomic diffusion is the key factor for the formation of superconducting phase. • Interphases of orthorhombic Fe(Se,Te)₂ and (Se,Te)_ss were formed during sintering. - Abstract: The phase evolution mechanism in Fe(Se, Te) system during sintering was investigated with step-by-step heat treatment process. It was noticed that the diffusion processes between Fe and Se (Te) as well as that between Se and Te were both very important to the formation of superconducting Fe(Se, Te) phase with very uniform chemical composition. During heat treatment, solid solutions of (Se, Te)_ss with different chemical composition were formed with the diffusion of Se atoms into Te solids and Te atoms into Se melts, simultaneously. Then with the increasing temperature, Fe atoms diffused into (Se, Te)_ss, Fe(Se, Te)₂ and Fe(Se, Te) phases were formed in sequence with the increasing Fe content. The chemical composition in melts became more and more uniform with the further increasing of sintering temperature and dwell time. Therefore, it was suggested that in order to achieve Fe(Se, Te) phase with high superconducting properties, it was necessary to enhance the diffusion process during sintering. The critical temperature of the sample, which was sintered at 700 °C for 12 h with slow cooling process and an O₂-annealing process for 24 h, was above 14.0 K. This T_c value proved that a good superconducting β phase could be obtained under this sintering condition.