Neutron diffraction studies on the liquid Te and As-Te mixtures

Neutron diffraction measurements for liquid (l-) Te and l-As-Te mixtures (10, 20, 30 and 40 at.% As) have been performed. The first minimum after the first peak of g(r) for l-Te and l-As-Te mixtures is filled up with temperature, and the second peak diminishes substantially and flattens out at high temperature. The temperature variations of g(r) are discussed combining the structural information available from EXAFS and computer simulation results. We propose that the volume contraction near the semiconductor to metal (S-M) transition causes the shrinkage of the inter-chain distance, and the short-and long-distance inter-chain correlations may coexist at high temperature. In the metallic region the -As-Te- chains are inferred to have nearly the same configuration as in l-Te. The prepeak near Q = 1.1-1.5 Å^-1 is observed for l-As₂₀Te₈₀ and l-As₄₀Te ₆₀, which diminishes with increasing temperature. The prepeak in l-As₄₀Te₆₀ lies at lower Q region compared with l-As ₂₀Te₈₀. It is concluded that the S-M transition observed for l-Te and l-As-Te mixtures is associated with the transformation to the densely packed configuration composed of shortened chain molecules.