Anharmonic temperature factors of zinc selenide determined by X-ray diffraction from an extended-face crystal

Generalized structure factor expressions are derived for the zinc blende structure. Inclusion of dispersion corrections is shown to give rise to the breakdown of Friedel's law for all-even-index reflections, an effect due to the presence of bonding or anharmonicity. X-ray intensity measurements from an extended-face crystal are interpreted within the generalized structure factor formalism to yield the B factors B_Zn = 1.020 ± 0.005 Ų and B_Se = 0.739 ± 0.008 Ų and an effective cubic anharmonic thermal parameter _ZnSe = β_Zn/α³_Zn - β_Se/α³_Se = --(6.8 ± 1.1) × 10³⁶ J^-2 ų at 296 K. These are compared with values for other zinc blende compounds and with theoretically calculated B factors.