High-pressure synthesis, crystal structure, and properties of the first ternary hafniumborate {beta}-HfB{sub 2}O{sub 5}

• Published in: Journal of solid state chemistry Vol. 180; no. 2
• Main Authors: Knyrim, Johanna S., Huppertz, Hubert
• Format: Journal Article
• Language: English
• Published: United States 15.02.2007
• Subjects: BORATES; HAFNIUM COMPOUNDS; HAFNIUM IONS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LATTICE PARAMETERS; LAYERS; MONOCLINIC LATTICES; PRESSURE RANGE GIGA PA; SPACE GROUPS; SYNTHESIS; TEMPERATURE RANGE 1000-4000 K; X-RAY DIFFRACTION
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2006.12.005

The first ternary hafniumborate {beta}-HfB{sub 2}O{sub 5} was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 deg. C. The monoclinic hafnium-diborate crystallizes with four formula units in the space group P2{sub 1}/c with lattice parameters a=438.48(9), b=690.60(2), c=897.60(2) pm, and {beta}=90.76(3){sup o}. 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 BO{sub 4} tetrahedra; between the layers, the hafnium ions are coordinated square-antiprismatically by eight oxygen atoms. A structural comparison of {beta}-HfB{sub 2}O{sub 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. - Graphical abstract: Synthesis of {beta}-HfB{sub 2}O{sub 5} via the multianvil high-pressure/high-temperature technique, representing the first ternary compound in the borate system Hf-B-O.