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Polymorphs of the Gadolinite‐Type Borates ZrB 2 O 5 and HfB 2 O 5 Under Extreme Pressure
Author(s) -
Pakhomova Anna,
Fuchs Birgit,
Dubrovinsky Leonid S.,
Dubrovinskaia Natalia,
Huppertz Hubert
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202005244
Subject(s) - isostructural , boron , metastability , crystallography , tetrahedron , high pressure , materials science , crystal structure , synchrotron , diffraction , phase (matter) , chemistry , thermodynamics , physics , organic chemistry , nuclear physics , optics
Based on the results from previous high‐pressure experiments on the gadolinite‐type mineral datolite, CaBSiO 4 (OH), the behavior of the isostructural borates β ‐HfB 2 O 5 and β ‐ZrB 2 O 5 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 ‐ZrB 2 O 5 features a rearrangement of the corner‐sharing BO 4 tetrahedra, while still maintaining the four‐ and eight‐membered rings. The new phase γ ‐HfB 2 O 5 contains ten‐membered rings including the rare structural motif of edge‐sharing BO 4 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 Hf 4+ , and tenfold coordinated Zr 4+ , 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.