Nuclear quadrupole resonance study of local bonding in glassy AsxSe1-x

Abstract

Nuclear quadrupole resonance (NQR) experiments were performed on glassy AsxSe1-x to study the local structural order. The bonding in AsxSe1-x is governed by preferential bonding (chemical ordering) between arsenic and selenium at arsenic concentrations x <= 0.40; however, the bonding for higher arsenic concentrations is governed mostly by statistical considerations. At concentrations x >= 0.45 the glasses are inhomogeneous with the presence of local regions of different composition. Measurements of the NQR spin echo intensity identify regions formed by arsenic atoms bonded to zero, one, two, or three selenium atoms. The NQR spectral line shapes and the longitudinal relaxation times suggest that these regions have a more ordered structure as compared to the homogeneous samples with low arsenic content. The existence of a small concentration of crystalline inclusions in amorphous As0.60Se0.40 is also suggested.