Pressure-Induced Structural Transitions in Liquid Metals and Semiconductors

2006 Fiscal Year Final Research Report Summary

• Project/Area Number: 16340110
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Condensed matter physics II
• Research Institution: Keio University
• Principal Investigator: TSUJI Kazuhiko Keio University, Faculty of Science and Technology, Professor, 理工学部, 教授 (10114563)
• Co-Investigator(Kenkyū-buntansha): CHIBA Ayano Keio University, Faculty of Science and Technology, Assistant Researcher, 理工学部, 助手 (20424195)
• Project Period (FY): 2004 – 2006
• Keywords: liquids / high pressure / phase transitions / structure / synchrotron radiations / x-ray diffraction

Research Abstract

The purpose of this project is to investigate the pressure dependence of the local structure and physical properties of liquids in which atoms have several kinds of bonds, such as covalent bond, ionic bond, metallic bond and weak bond. Results are discussed in relation to the pressure-induced phase transitions in the crystalline phase.
X-ray diffraction measurements under high pressure were performed by using synchrotron radiations with an energy-dispersive method. Pressure was generated by a multi-anvil apparatus. A sharp structural change was observed in liquid AgI. On the other hand, a continuous structural change was observed in liquid CuI, liquid CuBr and liquid CuCl. The local structure of liquid copper halides consists of tetrahedron structure at normal pressure and changes to octahedron structure with increasing pressure. The transition pressure for the liquids increases from CuCl to CuI, similar to the crystals. The pressure dependence of the local structure of copper halides i n which atoms have highly ionic bonds is similar to that of crystal, which is similar to that of liquid CdTe with highly ionic bonds.
In the liquid IV-VI compounds, whose crystal structure consists of two dimensional network of the covalent bonds, an anisotropic volume contraction was observed in liquid GeSe, liquid GeTe, liquid SnTe and liquid PbTe. A sharp structural change with pressure was observed in liquid GeTe between 1.8 GPa and 4.0 GPa, in liquid PbTe between 2.6 GPa and 4.0 GPa, in liquid SnTe between 1.6 GPa and 3.3 GPa and above the transition pressure, the pressure derivative of several structural parameters changes its value.
A new technique for electrical resistance measurements under high pressure was developed. Measurements under pressure shows the drastic increase of the conductivity with increasing temperature in GaSb and CdTe. However, the detailed pressure dependence measurements of the conductivity was unfinished.
From these results it is concluded that the pressure variation of the local structure of liquids depends on the ionicity in the bonds between atoms and the pressure-induced structural change of liquid IV-VI compounds is different from that of crystals.