Elastic, phononic, magnetic and electronic properties of quasi-one-dimensional PbFeBO4

Abstract

The diverse and interesting properties of mullite-type PbFeBO4 have resulted in a growing number of publications, using both experimental and computational methodologies. However, several questions remain to be explored such as the role of the magnetic configuration on the intrinsic potential anharmonicity at a microscopic level, and on the elastic properties and associated pressure-induced response of the nuclear structure. We thus employ the hybrid method PW1PW to study the structural, phononic, magnetic and electronic properties of PbFeBO4 at four different magnetic configurations. The magnetic configuration-driven strong anisotropy of the properties is correlated to two structural features, namely, the one-dimensional chains of FeO6 octahedra and the stereochemical activity of the lone electron pairs of Pb2+ cations. We propose a mechanism to explain the observed axial negative linear compressibility in the b direction. The vibrational features demonstrate insights into the anharmonic behavior of the structure, and a large fraction of modes with negative mode Grüneisen parameters. By optimizing four different magnetic configurations at different pressures the associated spin exchange parameters are calculated; the magnetic configuration considerably affects the magneto-elastic behavior of the structure. Optical absorption spectra calculated by GW0-BSE show a strong anisotropy, associated with the quasi-one-dimensional character of the structure given by the FeO6 chains.