Temperature and pressure dependence of the Si(222) forbidden reflection and the vibration of the bonding charge

The variation of the integrated intensities was measured between room temperature and 600 °C using a high-power x-ray generator. The pressure dependence was also measured up to 5.2 kbar and found to be so small that the implicit temperature dependence can be neglected. By making corrections for the effect of anharmonic vibration of nucleus using the neutron data obtained by Keating et al., the temperature coefficient of the bonding-charge component of the structure factor was obtained to be $(0.90\mathrm{}\pm 0.10)M_c$, where $M_c$ is the ordinary Debye-Waller factor with the Debye temperature of 540 °K. Simple calculation of the displacement of the bonding charge was made by assiming that the point bonding charges are always located at the midpoint between neighboring atoms. The ratio of the mean-square amplitude of the bonding charge to that of core was calculated to be 0.74 ± 0.05, which has a fairly good agreement with the value measured. Also the structure factor of the (222) reflection was obtained by the Pendellösung fringe method to be ${1.50}_5$ ± 0.015 at 20 °C.