The Pb2MgTeO6 double perovskite is cubic at high temperature and becomes incommensurately modulated with a rhombohedral R3̄ average structure at lower temperatures. Both the cubic and rhombohedral average structures are investigated using the local-density approximation within the density-functional theory: We determine the electronic, structural, dielectric, and zone-center dynamical properties. The computed structural parameters are in reasonable agreement with the experiment, with differences up to 2% for the lattice constants. There are two unstable zone-center vibration modes in the cubic phase. The first unstable mode T1g, 91.19i cm-1, has an antiferrodistortive character, while the second, T1u, 13.92i cm-1, has a ferrodistortive character. There is no unstable zone-center mode in the rhombohedral phase. We establish the correspondence between the zone-center modes in the two phases.
|Number of pages||7|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 1 May 2002|