Determination of bond strengths of arsenic and arsenic chalcogen compounds using the temperature dependence of extended x-ray-absorption fine structure

We present an extended x-ray-absorption fine-structure (EXAFS) study of the temperature dependence of crystalline (c-), As, ${\mathrm{As}}_2$ ${\mathrm{S}}_3$, and ${\mathrm{As}}_4$ ${\mathrm{S}}_4$, amorphous (a-) As, and glassy (g-) ${\mathrm{As}}_2$ ${\mathrm{S}}_3$. Based on an Einstein model, we find that the mean-square relative displacement of these materials in the first shell is primarily attributable to bond-stretching modes of vibration. From a comparison with Raman spectra, it is evident that the Einstein vibrational frequencies derived from EXAFS measurements are related to the effective bond-stretching force constants. Our results indicate that As—As bonds in c-As are about 17% weaker than those in a-As. Both stretching forces of the As—S bonds in c- and g-${\mathrm{As}}_2$ ${\mathrm{S}}_3$ are quite similar. The calculation of bond strengths in c-${\mathrm{As}}_4$ ${\mathrm{S}}_4$ shows that As—S bonds are about 30% stronger than As—As bonds. This work underscores the fact that temperature-dependent extended x-ray-absorption fine-structure data may be used to provide information about the nature—i.e., the strength—of the local bonding.