Polymorphs of the Gadolinite-Type Borates ZrB₂O₅ and HfB₂O₅ Under Extreme Pressure

Titelangaben

Pakhomova, Anna ; Fuchs, Birgit ; Dubrovinsky, Leonid ; Dubrovinskaia, Natalia ; Huppertz, Hubert:
Polymorphs of the Gadolinite-Type Borates ZrB₂O₅ and HfB₂O₅ Under Extreme Pressure.
In: Chemistry : a European Journal. Bd. 27 (2021) Heft 19 . - S. 6007-6014.
ISSN 1521-3765
DOI: https://doi.org/10.1002/chem.202005244

Volltext

Link zum Volltext (externe URL):

Abstract

Based on the results from previous high-pressure experiments on the gadolinite-type mineral datolite, CaBSiO4(OH), the behavior of the isostructural borates β-HfB2O5 and β-ZrB2O5 have been studied by synchrotron-based in situ high-pressure single-crystal X-ray diffraction experiments. On compression to 120 GPa, both borate layer-structures are preserved. Additionally, at ≈114 GPa, the formation of a second phase can be observed in both compounds. The new high-pressure modification γ-ZrB2O5 features a rearrangement of the corner-sharing BO4 tetrahedra, while still maintaining the four- and eight-membered rings. The new phase γ-HfB2O5 contains ten-membered rings including the rare structural motif of edge-sharing BO4 tetrahedra with exceptionally short B−O and B⋅⋅⋅B distances. For both structures, unusually high coordination numbers are found for the transition metal cations, with ninefold coordinated Hf4+, and tenfold coordinated Zr4+, respectively. These findings remarkably show the potential of cold compression as a low-energy pathway to discover metastable structures that exhibit new coordinations and structural motifs.