NEUTRON-DIFFRACTION STUDY OF LIQUID (TL1 2PB1/2)-X (X-TE,SE) SYSTEMS/

Neutron diffraction measurements have been carried out on liquid (TI1/ 2Pb1/2)(1-y)X(y)(X:Te,Se) systems which exhibit a typical compound-for ming behaviour at y = 3/7. Radial distribution analysis at y = 3/7 has indicated that the bonding nature of T1-X and Pb-X is more or less io nic, as expected from the previous result of electronic properties. In order to investigate the difference in electronic behaviour between t hese 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 > 3/7 is independent of the alloy composition. g(Se-Se)( r) has a well-resolved first peak at r similar to 0.230 nm, suggesting that covalent Se-Se bonds appear in the Se rich region. On the other hand, g(Te-Te)(r) is somewhat structureless, although the first peak i s 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.