Thermal expansion of coesite determined by synchrotron powder X-ray diffraction

Thermal expansion of synthetic coesite was studied with synchrotron powder X-ray diffraction in the temperature range of 100–1000 K. We determined the unit cell parameters of monoclinic coesite (a, b, c, and β) every 50 K in this temperature range. We observed that a and b parameters increase with increasing temperature, while c decreases. The β angle also decreases with temperature and approaches 120°. As a result, the unit cell volume expands by only 0.7% in this temperature range. Our measurements provide thermal expansion coefficients of coesite as a function of temperature: it increases from 3.4 × 10−6 K−1 at 100 K to 9.3 × 10−6 K−1 at 600 K and remains nearly constant above this temperature. The Suzuki model based on the zero-pressure Mie–Gruneisen equation of state was implemented to fit the unit cell volume data. The refined parameters are \({V_0}\) = 546.30(2) A3, \(Q\) = 7.20(12) × 106 J/mol and \({\theta _{\text{D}}}\) = 1018(43) K, where \({\theta _{\text{D}}}\) is the Debye temperature and \({V_0}\) is the unit cell volume at 0 K with an assumption that \({K^\prime }\) is equal to 1.8. The obtained Debye temperature is consistent with that determined in a previous study for heat capacity measurements.