Rietveld Analysis of a High Pressure Modification of Monocalcium Oxogallate (CaGa 2 O 4 )

Vollständiger Abstract

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Abstract A high‐pressure modification of monocalcium gallate (CaGa 2 O 4 ) has been prepared in a piston‐cylinder apparatus at 700 °C and 4.0 GPa. The compound is orthorhombic (space group Pnam , a = 9.12476(15) Å, b = 10.56093(18) Å, c = 2.98547(4) Å, V = 287.70(1) Å 3 , Z = 4, D calc = 5.62 g/cm 3 ) and belongs to the CaFe 2 O 4 ‐type structure family. The structure was refined by the Rietveld method using laboratory X‐ray powder diffraction data. Two crystallographically independent GaO 6 ‐octahedra forming edge‐sharing double chains can be distinguished. The shared edges exhibit a considerable shortening. The chains are running parallel to the c ‐axis and are linked by corner‐sharing. They enclose tunnels in which the calcium atoms are located for charge compensation. Each calcium cation has eight nearest oxygen neighbors. The coordination environment can be described as a bicapped trigonal prism.