Structure and Electronic Properties of Te–Se Mixtures under High Pressure

X-ray diffraction and electrical resistance have been measured for amorphous and crystalline Te 1- x Se x mixtures (0≤ x ≤1) under high pressure up to 30 GPa, and four high pressure phases of Te-Se mixtures have been observed: a monoclinic phase with 6 atoms per unit cell (M-I phase); a monoclinic phase with 4 atoms per unit cell (M-II phase); an orthorhombic phase; a β-Po-type phase. It was found for the first time that the M-II phase containing ∼60 at.% Se can be quenched to the atmospheric pressure. X-ray diffraction, EXAFS (extended X-ray absorption fine structure) and optical reflectivity have been measured for the pressure-quenched Te 0.4 Se 0.6 specimens. Pressure-quenched Te 0.4 Se 0.6 belongs to the space group C m and has a puckered layer structure containing planer zigzag chains with period 3. Moreover, the superlattice structure with a unit cell size of 9 lattice constants along the b-axis was found. The EXAFS results suggest the existence of chemical short range order. We discuss the correlation between the structure and the electronic states in the high-pressure phases of Te-Se mixtures.