High-pressure synthesis, crystal structure, and properties of the first ternary hafniumborate beta-HfB2O5

摘要

The first ternary hafniumborate beta-HfB2O5 was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 degrees C. The monoclinic hafnium-dibo rate crystallizes with four formula units in the space group P2(1)/c with lattice parameters a = 438.48(9), b = 690.60(2), c = 897.60(2) pm, and beta = 90.76(3)degrees. Due to the fact that high-pressure conditions favour the fourfold-coordination of boron, a structure is observed, which is built up exclusively from layers of BO4 tetrahedra; between the layers, the hafnium ions are coordinated square-antiprismatically by eight oxygen atoms. A structural comparison of beta-Hf beta O-2(5) with minerals of the gadolinite-homilite-hingganite-datolite family proved this compound to be the simplest structural variant in this structure type, known so far. Along with a structural discussion, temperature-programmed X-ray powder diffraction data are shown, demonstrating the metastable character of this compound. (c) 2006 Elsevier Inc. All rights reserved.