Lattice dynamical properties of antiferromagnetic rocksalt oxides are often interpreted using the cubic space group Fm (3) over barm, although below Neel temperature their magnetic substructure possesses a lower symmetry. For example, in the case of NiO, a rhombohedral structural distortion lowers the symmetry to trigonal space group R (3) over barm below 525 K. We performed hybrid density functional theory calculations on the phonon dispersion relations of MnO, CoO, and NiO, and the lattice thermal conductivity of NiO using both Fm (3) over barm and R (3) over barm space groups. The calculated acoustic phonon frequencies of all oxides agree well with the available experimental data, while the optical modes of MnO and CoO show somewhat larger discrepancies. Our calculations show the phonon density of states to be very similar with both studied space groups. The experimental thermal conductivity of antiferromagnetic NiO is reproduced well below the Neel temperature by solving the linearized phonon Boltzmann transport equation.
01/09/2018 → 31/08/2022
Projekti: Academy of Finland: Other research funding
01/04/2016 → 23/09/2019
Projekti: Academy of Finland: Strategic research funding