Compression behaviors of distorted rutile-type hydrous phases, MOOH (M = Ga, In, Cr) and CrOOD

歪んだルチル型構造をとる含水相MOOH(M=Ga, In, Cr) and CrOODの圧縮挙動

佐野 亜沙美   ; 八木 健彦*; 岡田 卓*; 後藤 弘匡*; 亀掛川 卓美*

Sano, Asami; Yagi, Takehiko*; Okada, Taku*; Goto, Hirotada*; Kikegawa, Takumi*

歪んだルチル型構造をとる含水相-GaOOH, InOOH, -CrOOH, -CrOODについて高圧下におけるX線回折実験を行った。-GaOOH, InOOHでは15GPa, -CrOODでは4GPaで高圧下で軸比の圧力応答に変化が見られ、水素結合のあるa軸及びb軸が圧縮されにくくなることが明らかになった。圧縮挙動の変化が起きる圧力は、水素結合を含む酸素-酸素間距離が長いほど、高圧になる傾向が見られた。一方で常圧下において非常に強い水素結合を持つ-CrOOHではそのような変化は見られなかった。これらの挙動は以前-AlOOH(D)で報告された、水素結合の対称化に伴う圧縮挙動の変化に対応していると考えられる。

X-ray diffraction measurements of distorted rutile-type oxyhydroxides -GaOOH, InOOH, -CrOOH, and -CrOOD were taken at a maximum pressure of up to 35 GPa under quasi-hydrostatic conditions, at ambient temperature. Anomalies in the evolution of the relative lattice constants and the axial ratios of -GaOOH, InOOH, and -CrOOD suggest anisotropic stiffening along the a- and/or b-axes where the hydrogen bond is formed. The changes were observed at 15 GPa in -GaOOH and InOOH and at 4 GPa in -CrOOD. The pressures were higher in oxyhydroxides that have longer O...O distances of the hydrogen bond at ambient pressure. In contrast, such stiffening behavior was not observed in CrOOH, which has a significant short O...O distance and strong hydrogen bond. The stiffening behaviors observed in the present study can be attributed to the symmetrization of the hydrogen bonds in oxyhydroxides, as was previously found in -AlOOH(D).