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Thermal properties of 2:1 bismuth borate: Temperature‐dependent characterizations of lone electron pairs
Author(s) -
Murshed M. Mangir,
Petersen Hilke,
Fischer Michael,
Curti Mariano,
Mendive Cecilia B.,
Baran Volodymyr,
Senyshyn Anatoliy,
Gesing Thorsten M.
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16042
Subject(s) - thermal expansion , debye model , lone pair , phonon , density functional theory , raman spectroscopy , materials science , anharmonicity , negative thermal expansion , condensed matter physics , bismuth , chemistry , thermodynamics , computational chemistry , physics , optics , organic chemistry , molecule , metallurgy
Abstract Applications of bismuth borate ceramics require understanding of the microscopic features, leading to macroscopic behaviors such as thermal expansion. We report the structural and spectroscopic features of Bi 4 B 2 O 9 between 4 K and 900 K using a combination of temperature‐dependent neutron and X‐ray powder diffractions and Raman spectroscopy. Lattice thermal expansion was modeled using the Debye‐Einstein‐Anharmonicity ( DEA ) fit. The model also follows four independent thermal expansion tensors of the monoclinic system. Phonon density of states obtained from the density functional theory ( DFT ) calculations helps to understand the low Debye temperature calculated from the metric expansion as well as from the isotropic atomic displacement parameters. Both Wang‐Liebau eccentricity ( WLE ) parameter and Liebau density vector ( LDV ) are calculated from the structural data and from the DFT calculation, respectively. Whereas, the dimensionless absolute value of WLE measures the degree of deformation of the electronic deformation density of the 6 s 2 lone electron pairs ( LEP s) of the Bi 3+ cations, LDV additionally shows the changes of the orientation of the LEP ‐lobes as function of temperature. Analyses of the temperature‐dependent frequencies of some selected Raman modes support the choice of the elastic model of the Debye approach.