Study of the Local Structure in Vitreous Chalcogenides via Measurement of Asymmetry of the Electric-Field-Gradient Tensor

The electric-field-gradient asymmetry parameter has been measured in several vitreous chalcogenides at arsenic sites which undergo a strong quadrupolar coupling. Results in vitreous ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ and ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$ reveal a cylindrical local symmetry which contrasts with the distortion associated with the lamellar structure crystalline ${\mathrm{As}}_2$ ${\mathrm{S}}_3$. However, in amorphous ${\mathrm{As}}_{25}$ ${\mathrm{Te}}_{75}$ and ${\mathrm{As}}_{45}$ ${\mathrm{Te}}_{55}$ the local environment of arsenic displays a sizable distortion.