日時 ： ２００９年１０月３０日（金）※16：30～
場所 ： 愛媛大学総合研究棟Ⅰ 4F 共通会議室（理学部構内）
要 旨
Phase transition under high pressure is significant to the study of the material properties and transformation mechanisms. Pressure-induced irreversible structural transitions always occur in the similar compounds LiMO2 (M = B, Al and Ga), where M is the element of ⅢA group of the Periodic Table. The LiMO2 compounds are considered to be a congruent compound of the Li2O-M2O3 system. Technologically, these compounds are attractive because of their potential applications in optoelectronics. This kind of A1+B3+O2 compounds can crystallize with two or more structures. With the pressure increase, their structures become more symmetrical, and the M ions tend to have higher coordination number (3 → 4 → 6). Previous studies only focused on the phase transitions of LiMO2 at some certain P-T points. In this work, we have studied the LiMO2 compounds over a wide range P-T condition (0.5-22 GPa, 27-1600 ℃) by means of XRD analysis, DTA measurements, FT-IR spectroscopy and FT-Raman spectroscopy. It has been found that LiBO2, LiAlO2 and LiGaO2 could experience first-order phase transitions to its polymorphs at relatively modest P-T conditions compared to the previously reported results. Besides the previously described polymorphic phases, a new high-pressure phase of LiGaO2 have been recovered by compressing the orthorhombic phase LiGaO2 at pressures above 13 GPa. The new phase may be indexed as a cubic structure with lattice parameter of a = 0.4105 nm. In addition, the P-T phase diagrams for LiBO2, LiAlO2 and LiGaO2 have also been defined for the first time. It is worthwhile to address similarities and differences in terms of the structure and spectroscopy between these similar compounds. It may lead to a better understanding of the phase evolution in the LiMO2 system.
問い合わせ先：土屋 卓久 TEL （089）927-8198
E-mail takut@sci.ehime-u.ac.jp
