Lattice constant of Bi$_2$Se$_3$ and Sb$_2$Te$_3$ crystals is determined by X-ray powder diffraction measurement in a wide temperature range. Linear thermal expansion coefficients ($alpha$) of the crystals are extracted, and considerable anisotropy between $alpha_parallel$ and $alpha_perp$ is observed. The low temperature values of $alpha$ can be fit well by the Debye model, while an anomalous behavior at above 150 K is evidenced and explained. Gruneisen parameters of the materials are also estimated at room temperature.
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