First-order character of the displacive structural transition in BaWO_4  

作　　者：谭大勇 肖万生 周微 陈鸣 熊小林 宋茂双 

机构地区：[1]Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences

出　　处：《Chinese Physics B》2012年第8期365-373,共9页中国物理B（英文版）

基　　金：Project supported by the National Natural Science Foundation of China (Grant Nos. 11179030 and 90714011);the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KJCX2-SW-N20)

摘　　要：Nearly all displacive transitions have been considered to be continuous or second order, and the rigid unit mode （RUM） provides a natural candidate for the soft mode. However, in-situ X-ray diffraction and Raman measurements show clearly the first-order evidences for the scheelite-to-fergusonite displacive transition in SaWO4： a 1.6% volume collapse, coexistence of phases, and hysteresis on release of pressure. Such first-order signatures are found to be the same as the soft modes in BaWO4, which indicates the scheelite-to-fergusonite displacive phase transition hides a deeper physical mechanism. By the refinement of atomic displacement parameters, we further show that the first-order character of this phase transition stems from a coupling of large compression of soft BaOs polyhedrons to the small displacive distortion of rigid WO4 tetrahedrons. Such a coupling will lead to a deeper physical insight in the phase transition of the common scheelite-structured compounds.Nearly all displacive transitions have been considered to be continuous or second order, and the rigid unit mode （RUM） provides a natural candidate for the soft mode. However, in-situ X-ray diffraction and Raman measurements show clearly the first-order evidences for the scheelite-to-fergusonite displacive transition in SaWO4： a 1.6% volume collapse, coexistence of phases, and hysteresis on release of pressure. Such first-order signatures are found to be the same as the soft modes in BaWO4, which indicates the scheelite-to-fergusonite displacive phase transition hides a deeper physical mechanism. By the refinement of atomic displacement parameters, we further show that the first-order character of this phase transition stems from a coupling of large compression of soft BaOs polyhedrons to the small displacive distortion of rigid WO4 tetrahedrons. Such a coupling will lead to a deeper physical insight in the phase transition of the common scheelite-structured compounds.

关 键 词：BaWO4 pressure-induced phase transitions X-ray diffraction Raman scattering 

分 类 号：P618.67[天文地球—矿床学]