Crystal structure and compressibility of a two-layer polytype of pseudowollastonite (CaSiO ₃ )

Carnegie Institution of Washington, Geophysical Laboratory and Center for High Pressure Research, Washington, DC, United States

The crystal structure of a synthetic two-layer polytype of CaSiO ₃ pseudowollastonite was determined using single-crystal X-ray diffraction data. It is monoclinic with space group C2/c and unit-cell parameters a = 11.8322(6), b = 6.8624(8), c = 10.5297(5) Aa, beta = 111.245(8) degrees , and V = 796.9(1) Aa ³ . The material is isostructural with two-layer SrSiO ₃ and SrGeO ₃ and has basic structural features similar to those found in four-layer CaSiO ₃ pseudowollastonite, except for the stacking sequence of layers of CaO ₆ octahedra and Si ₃ O ₉ ternary rings. The compressibility of the structure was measured up to 9.94 GPa and no phase transition was observed. With increasing pressure, all unit-cell parameters decrease nonlinearly with a positive curvature. The axial compression ratios at room pressure are beta _a :beta _b :beta _c = 2.25:2.36:1.00 and the bulk modulus, K _T , is 86(1) GPa with K' = delta K _T /delta P = 3.8(4).

This record provided courtesy of AGI/GeoRef.