Multianvil high-pressure/high-temperature synthesis, crystal structure, and thermal behaviour of the rare-earth borogermanate Ce6(BO4)2Ge9O22

The new monoclinic cerium borogermanate Ce6(BO4)2Ge9O22 was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 10.5 GPa and 1200 °C. Ce6(BO4)2Ge9O22 crystallizes with two formula units in the space group P21/n   with lattice parameters a=877.0(2)a=877.0(2), b=1079.4(2)b=1079.4(2), c=1079.1(2)c=1079.1(2) pm, and β=95.94(3)°β=95.94(3)°. 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.

Synthesis of the new borogermanate Ce6(BO4)2Ge9O22 via multianvil high-pressure techniques exhibiting BO4-tetrahedra, GeO6-octahedra, and oxygen atoms O[3] coordinated by one boron and two germanium atoms.Figure optionsDownload as PowerPoint slide