摘要：

Single crystals of Ca2Ga2O5 have been synthezised in a piston cylinder apparatus at 1250°C/2.5 GPa from precursors prepared by solid state reactions. The crystal structure has been investigated by X-ray diffraction methods. The compound crystallizes in the orthorhombic space group I2mb (a = 5.3525(1), b = 14.6666(1), c = 5.5651(1), V = 436.88(1)3, Z = 4, Dcalc=4.56 g cm-3 and is isotypic with Ca2FeAlO5 (Brownmillerite) and Ca2Al2O5. Basic building units of Ca2Ga2O5 are (1) layers of perovskite type corner connected GaO6-octahedra and (2) sheets comprised of zweier single chains of GaO4-tetrahedra. The alternate stacking of the two building units results in a threedimensional framework in which the calcium cations are incorporated for charge compensation. Dicalcium gallate is the first structurally characterized representative of a double oxide in the system CaO - Ga2O3showing a sixfold coordination of Ga3+.

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