中国物理B ›› 2012, Vol. 21 ›› Issue (8): 86201-086201.doi: 10.1088/1674-1056/21/8/086201

• CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES • 上一篇    下一篇

First-order character of the displacive structural transition in BaWO4

谭大勇, 肖万生, 周微, 陈鸣, 熊小林, 宋茂双   

  1. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
  • 收稿日期:2011-12-19 修回日期:2012-02-26 出版日期:2012-07-01 发布日期:2012-07-01
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 11179030 and 90714011) and the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KJCX2-SW-N20).

First-order character of the displacive structural transition in BaWO4

Tan Da-Yong (谭大勇), Xiao Wan-Sheng (肖万生), Zhou Wei (周微), Chen Ming (陈鸣), Xiong Xiao-Lin (熊小林), Song Mao-Shuang (宋茂双 )   

  1. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
  • Received:2011-12-19 Revised:2012-02-26 Online:2012-07-01 Published:2012-07-01
  • Contact: Xiao Wan-Sheng E-mail:wsxiao@gig.ac.cn
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 11179030 and 90714011) and the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KJCX2-SW-N20).

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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 BaWO4: 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 BaO8 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

Abstract: 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 BaWO4: 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 BaO8 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.

Key words: BaWO4, pressure-induced phase transitions, X-ray diffraction, Raman scattering

中图分类号:  (High-pressure effects in solids and liquids)

  • 62.50.-p
63.70.+h (Statistical mechanics of lattice vibrations and displacive phase transitions) 61.05.cp (X-ray diffraction) 78.30.-j (Infrared and Raman spectra)