Electronic structure, mechanical properties and thermal conductivity of Ln2Zr2O7 (Ln = La, Pr, Nd, Sm, Eu and Gd) pyrochlore

The electronic structure, chemical bonding and mechanical properties of Ln2Zr2O7 (Ln = La, Pr, Nd, Sm, Eu and Gd) pyrochlore are investigated by local-density approximation of spin polarized scheme + U calculations (U is the Hubbard energy) and further verified by the experimental results. Ln2Zr2O7 compounds are wide band gap insulators, and this is consistent with the experiment results. The calculated spin polarized density of states of them indicates that they are in a ferromagnetic state and the magnetic moment is mainly attributed to the 4f shell of the Ln atoms. For the chemical bonds in the Ln2Zr2O7 crystals, the O-Zr bond is stronger than the O-Ln bond. The hardness, elastic constants, bulk modulus, shear modulus, Young's modulus and Poisson's ratio of Ln2Zr2O7 compounds are investigated and the theoretical values are in good agreement with the experiments. The mechanical anisotropic properties are discussed using Zener's indexes and universal elastic anisotropic index (AU). The sound velocities along [1 0 0], [1 1 0] and [1 1 1] directions are calculated for each Ln2Zr2O7 crystal. The thermal conductivities of Ln2Zr2O7 compounds are evaluated and the obtained thermal conductivity of Ln2Zr2O7 is lower than that of yttria-stabilized zirconia, indicating that they could be good low thermally conductive materials at high temperature.