Anisotropic lattice thermal expansion of PbFeBO4: a study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

MURSHED M.M.; MENDIVE C.; CURTI M.; NÉNERT G.; KALITA P.E.; LIPINSKA K.E.; CORNELIUS A.L.; HUQ A.; GESING TH. M.

MATERIALS RESEARCH BULLETIN

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2014 vol. 59 p. 170 - 178

0025-5408

The lattice thermal expansion of mullite-type PbFeBO4 is presented in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modelled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. The unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations.Harmonic frequencies of the optical Raman modes at the Gamma-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO4, FeO6 and BO3 polyhedra as a function of temperature.