Bonding-Electron Distributions, Anharmonicity, and the Temperature Dependence of the Forbidden Si(442) Reflection
- 15 November 1972
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 6 (10), 3659-3666
- https://doi.org/10.1103/physrevb.6.3659
Abstract
The forbidden Si(442) reflection was detected and its temperature dependence measured between 20 and 500°C using x-ray radiation. The reflection is extremely weak at room temperature with an integrated intensity of 4.6× and a structure factor . decreases to zero at 250°C and then increases to almost twice its room-temperature value at 500°C. This temperature dependence is consistent with contributions to the structure factor from both the antisymmetric bond charge distribution , and anharmonic thermal motion of the atoms . It was shown that is of opposite sign and larger in magnitude than at room temperature. The anharmonic contribution increases with temperature and cancels at about 250°C producing zero intensity. The combination of these measurements and a recent neutron determination of yielded at 25°C. This structure factor is the Fourier transform of the valence-electron distribution and like the (222) structure factor, provides a sensitive check on the accuracy of the wave functions determined from band calculations. The values of show a tendency to be temperature independent. However, rather large experimental errors due to the very low intensities prevented conclusions about the temperature dependence of .
Keywords
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