論文

Dynamic structures of liquid Te 70 Se 30 and Te 50 Se 50 were investigated by inelastic neutron scattering experiments in the semiconductor-to-metal transition range. The bond-stretching modes for the both liquid mixtures were found to clearly soften when the transition occurs. We discuss the change of static and dynamic structures that accompany the transition.

液体Se, Te50Se50 について中性子非弾性散乱測定を行った。結晶のトリゴナル相よりも液体相の結合伸縮モードが高エネルギー側にシフトしているのが観測された。これは鎖状分子が液体において孤立していることを示している。同モードの強度の波数依存性を解析した結果、そのピーク位置が、単純な２体の動的相関によって説明できることが分かった。用いたモデルは２体の逆位相の動きを仮定した。３体モデルによってよりよく実験結果を再現できることも分かった。この解析法によって、孤立した分子においては波数依存性の解析から短距離構造を引き出すことができる。

Neutron scattering measurements were carried out for liquid Se, liquid Te, and liquid Te50Se50. The results are discussed in the context of semiconductor-to-metal transition. As to liquid Te50Se50, the vibrational modes show a remarkable change when the semiconductor-to-metal transition occurs by temperature increase. A soft stretching mode was observed for the metallic phase and it shows the structural change; the appearance of long bonds in the metallic phase. The vibrational modes for liquid Se and liquid Te were obtained and agreed well with former works. The crossover from collective to single-particle-like regime was also observed for all liquid samples and the transition ranges (Q = 4.5–8 Å–1) are presented. The diffusive features in the low-Q region and single-particle-like properties in the high-Q region are discussed and are shown to be consistent with the results for the vibrational modes.

We have carried out neutron scattering experiments for liquid Te50Se50 at 700 K (semiconducting regime), 900 K (transition regime) and 1100 K (metallic regime). The quasielastic scattering peak is comparatively narrow at the peak positions of S(Q). A remarkable increase in the peak width is observed near the first minimum of S(Q), when the semiconductor-to-metal transition occurs. Since the first peak of S(Q) in this system proves to mainly reflect the inter-chain correlation and the second peak to the intra-chain correlation, the observed broadening may suggest frequent bond-switching between the chains in the metallic regime.

液体Se2Cl2, Se2Br2 の中性子非弾性散乱およびラマン散乱測定を行った。今回の実験結果は、過去の振動モードの報告と概ね良い一致を得たが、結合角についての振動モードはラマン散乱と中性子散乱で異なる結果を得た。両手法で観測できる波数が異なるので、振動モードに微弱ながら分散があるためであると考えることができる。