High-pressure synthesis of metastable Bi-S crystalline compounds: Crystal structure and electron transport

A new metastable Bi3S4 single crystal has been obtained on the initial Bi: S = 2 : 3 mixture at a pressure of 8.0-8.5 GPa with slow cooling from 1300 to 800 degrees C at a rate of similar to 3 degrees C/min followed by quenching. The crystal has a triclinic structure formed by Bi-centered S-polyhedrons and chain-like clusters of Bi atoms. The relationship between the triclinic model based on single-crystal X-ray diffraction data and the orthorhombic model previously proposed for high-pressure Bi-S and Bi-Se phases with a similar structural motif based on X-ray powder diffraction data is discussed. The new Bi3S4 phase is a narrow-gap (band gap of 0.234 eV) intrinsic n-type semiconductor with a shallow impurity level. Metastable Bi3S4 recovers the structure of bismuthinite Bi2S3 after annealing at 200 degrees C.