Local atomic strain in ${\mathrm{ZnSe}}_{1-x}{\mathrm{Te}}_x$ from high real-space resolution neutron pair distribution function measurements

High real-space resolution atomic pair distribution functions (PDF’s) have been obtained from ${\mathrm{ZnSe}}_{1-x}{\mathrm{Te}}_x$ using neutron powder diffraction. Distinct Zn-Se and Zn-Te nearest-neighbor (nn) bonds, differing in length by $\Delta r=0.14\mathrm{}$ Å, are resolved in the measured PDF’s, allowing the evolution with composition of the individual bond lengths to be studied. The local bond lengths change much more slowly with doping than the average bond length obtained crystallographically. The nn bond-length distributions are constant with doping, but higher-neighbor pair distributions broaden significantly, indicating that most of the strain from the alloying is accommodated by bond-bending forces in the alloy. PDF’s of alloys across the whole doping range are well fit using a model based on the Kirkwood potential. The resulting PDF’s give excellent agreement with the measured PDF’s over the entire alloy range with no adjustable parameters.