A first principles study on the phonon transport in layered BiCuOSe
First principles calculations are employed to investigate the phonon transport of BiCuOSe. Our calculations reproduce the lattice thermal conductivity of BiCuOSe. The calculated gruneisen parameter is 2.4 2.6 at room temperature, a fairly large value indicating a strong anharmonicity in BiCuOSe, which leads to its ultralow lattice thermal conductivity. The contribution to total thermal conductivity from high frequency optical phonons, which are mostly contributed by the vibrations of O atoms, is larger than 1/3, remarkably different from the usual picture with very little contribution from high frequency optical phonons. Our calculations show that both the high group velocities and low scattering processes involved make the high frequency optical modes contribute considerably to the total lattice thermal conductivity. In addition, we show that the sound velocity and bulk modulus along a and c axes exhibit strong anisotropy, which results in the anisotropic thermal conductivity in BiCuOSe.
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