Comprehensive Interpretation of a Substitution Effect on an Order-Disorder Phase Transition in A1-xMxW2O8-

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• 作者：Yasuhisa Yamamura ; Kenichi Masago ; Masayuki Kato ; Toshihide Tsuji
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：August 30, 2007
• 年：2007
• 卷：111
• 期：34
• 页码：10118 - 10122
• 全文大小：107K
• 年卷期：v.111,no.34(August 30, 2007)
• ISSN：1520-5207

文摘

Hf_1-xLu_xW₂O_8-y solid solutions up to x = 0.04, based on a negative thermal expansion material HfW₂O₈,were synthesized by a solid sate reaction method. X-ray diffraction experiments of these solid solutions from90 to 560 K indicated thermal contraction with increasing temperature. Temperatures of order-disorder phasetransition (T_trs) associated with the orientation of WO₄ tetrahedra were determined from disappearance of acharacteristic diffraction peak (310). The T_trs of the solid solutions drastically decreased with increasing Lucontent. Saturated order parameters (_s) associated with the orientational order of the WO₄ pairs were estimatedfrom the characteristic diffraction peak at sufficient low temperature. These behaviors of Hf_1-xLu_xW₂O_8-yare consistent with those of Zr_1-xM_xW₂O_8-y (M = Sc, Y, In, Lu). The drastic suppression of T_trs inHf_1-xLu_xW₂O_8-y can be interpreted in the framework of a model proposed for Zr_1-xM_xW₂O_8-y, which statesthe existence of a local nanoregion including the WO₄ pairs having the frozen-in orientational disorder. Tounderstand the substitution effect on the order-disorder phase transition comprehensively, classification basedon the saturated order parameter _s of the phase transition of AW₂O₈ (A = Hf, Zr)-based solid solutions wascarried out and discussed.