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The electronic structure, anisotropic elastic and thermal properties of monoclinic Ca₂Nb₂O₇

have been investigated by density functional theory (DFT) calculations and further are

verified by experimental results. It has been shown that the monoclinic Ca₂Nb₂O₇ 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

Ca₂Nb₂O₇ has low limit thermal conductivity with 1.43 Wm⁻¹K⁻¹ at high temperature,

and minimum thermal conductivity in (100), (110), (010) and (001) planes sensitively

depends on the directions.
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