Neutron diffraction study of liquid (Tl_1/2Pb_1/2)-X(X:Te, Se) systems

Neutron diffraction measurements have been carried out on liquid (Tl_1/2 Pb_1/2)_1-y X_y (X:Te,Se) systems which exhibit a typical compound-forming behaviour at y = frac(3, 7). Radial distribution analysis at y = frac(3, 7) has indicated that the bonding nature of Tl{single bond}X and Pb{single bond}X is more or less ionic, as expected from the previous result of electronic properties. In order to investigate the difference in electronic behaviour between these two liquid systems in the chalcogen rich region, we derive the X-X partial distribution function g_X-X(r, assuming that each partial function at y > frac(3, 7) is independent of the alloy composition. g_Se-Se(r) has a well-resolved first peak at r ∼ 0.230 nm, suggesting that covalent Se{single bond}Se bonds appear in the Se rich region. On the other hand, g_Te-Te(r) is somewhat structureless, although the first peak is included in the covalent region. The whole functional form of both g_X-X(r) is roughly similar to that of g (r) in pure liquid Te or Se.