Multianvil high-pressure/high-temperature synthesis, crystal structure, and thermal behaviour of the rare-earth borogermanate Ce-6(BO4)(2)Ge9O22

摘要

The new monoclinic cerium borogermanate Ce-6(BO4)(2)Ge9O22 was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 10.5 GPa and 1200 degrees C. Ce-6(BO4)(2)Ge9O22 crystallizes with two formula units in the space group P2(1) with lattice parameters a = 877.0(2), b = 1079.4(2), c = 1079.1(2) pm, and beta = 95.94(3)degrees. As the parameter pressure favours the formation of compounds with cations possessing high coordination numbers, it was possible to produce simultaneously BO4-tetrahedra and GeO6-octahedra in one and the same borogermanate for the first time. Furthermore, the cerium atoms show high coordination numbers (C.N.: 9 and 11), and one oxygen site bridges one boron and two germanium atoms O-[3]), which is observed here for the first time. Besides a structural discussion, temperature-dependent X-ray powder diffraction data are presented, demonstrating the metastable character of this high-pressure phase. (C) 2005 Elsevier Inc. All rights reserved.