The effects of pressure and temperature on the lattice constants and thermal expansion coefficients of Indium were studied up to 18.6 GPa and 506 K based on in situ X-ray diffraction method with an externally heated diamond anvil cell. The results show that the measured axial ratio (c/a) decreases with increasing temperature and its temperature dependence decreases with increasing pressure. The thermal expansion coefficient of the a-axis decreases with increasing pressure up to 7 GPa and remains almost constant above 7 GPa, whereas that of the c-axis increases monotonously with pressure and changes from negative to positive at around 7 GPa. The observed behavior suggests that temperature reduces the tetragonal distortion on the lattice, and its effect is dominant below 7 GPa; in contrast, pressure enhances lattice distortion, and tends to have a stronger effect above 7 GPa.
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