High-pressure Syntheses and Crystal Structures of Monoclinic B-Ho2O3 and Orthorhombic HoGaO3

Monoclinic holmium sesquioxide B-Ho2O3 and orthorhombic holmium orthogallate HoGaO3 were synthesized in a Walker-type multianvil apparatus under high-pressure / high-temperature conditions of 11.5 GPa / 1250 degrees C and 7.5 GPa / 1250 degrees C, respectively. Both crystal structures could be determined by single-crystal X-ray diffraction data, collected at r. t. The monoclinic holmium oxide crystallizes in the space group C2/m (Z = 6) with the parameters a = 1394.7(3), b = 350.83(7), c = 865.6(2) pm, beta = 100.23(3)degrees, R1 = 0.0517 wR2 = 0.1130 (all data), and the orthorhombic compound HoGaO3 in Pnma (Z = 4) with the parameters a = 553.0(2), b = 753.6(2), c = 525.4(2) pm, R1 = 0.0222, and wR2 = 0.0303 (all data).