Pressure-induced dehydration of dioptase: A single-crystal X-ray diffraction and Raman spectroscopy study | CU Experts

; We present a synchrotron-based, single-crystal X-ray diffraction and Raman spectroscopy study of natural green dioptase (Cu; 6; Si; 6; O; 18; ·6H; 2; O) up to ∼30 GPa at room temperature. The lattice parameters of dioptase exhibit continuous compression behavior up to ∼14.5 GPa, whereupon a structural transition is observed. Pressure–volume data below 14.5 GPa were fitted to a second-order Birch–Murnaghan equation of state with; V; 0; = 1440(2) Å; 3; and; K; 0; = 107(2) GPa, with; K; 0; ′ = 4(fixed). The low-pressure form of dioptase exhibits anisotropic compression with axial compressibility; β; ; a; ; > ; β; ; c; ; in a ratio of 1.14:1.00. Based on the diffraction data and Raman spectroscopy, the new high-pressure phase could be regarded as a dehydrated form of dioptase in the same symmetry group. Pressure-induced dehydration of dioptase contributes broadly to our understanding of the high-pressure crystal chemistry of hydrous silicates containing molecular water groups.;

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