Electronic structure, anisotropic elastic and thermal properties of monoclinic Ca2Nb2O7

• DOI: 10.1016/j.ceramint.2016.02.169
• Publication Date: 2016-03-03T09:26:26Z
• Authors: Jun Yang; Meng Zhao; Muhammad Shahid; Jing Feng; Chunlei Wan; Wei Pan
• Keywords: Monoclinic crystal system

Abstract The electronic structure, anisotropic elastic and thermal properties of monoclinic Ca 2 Nb 2 O 7 have been investigated by density functional theory (DFT) calculations and further are verified by experimental results. It has been shown that the monoclinic Ca 2 Nb 2 O 7 is a direct band gap insulator with the calculated band gap of 3.07 eV which is comparable with the experimental value of 3.33 eV. The bottom of the conduction band (CB) is dominated by the 4d orbitals of the Nb atoms and the 2p orbitals of O atoms, while the top of valence band (VB) mainly consists of the 2p orbitals of O atoms. Calculated sound velocities of different directions show that the faster mixed mode ( v + ) is much larger than that of slower mixed mode ( v - ) and pure transverse mode ( v t ) in both [100] and [001] directions. The pure longitudinal mode v l has the greatest sound velocity among the three acoustic modes in the [010] direction. According to Clarke's model, monoclinic Ca 2 Nb 2 O 7 has low limit thermal conductivity with 1.43 Wm −1 K −1 at high temperature, and minimum thermal conductivity in (100), (110), (010) and (001) planes sensitively depends on the directions.