Nuclear quadrupole resonance study of local structure of the Ge-As-Se ternary chalcogenide glasses

The local bonding structure in the Ge-As-Se ternary glassy system has been investigated by As-75 nuclear quadrupole resonance (NQR) at 77 K. For the compositions with average coordination number (r) over bar = 2.2, 2.4, 2.54 the NQR measurements yield no evidence for the presence of As-As homopolar bonds. For the composition Ge2As2Se5 ((r) over bar = 2.67) the NQR lineshape exhibits two peaks corresponding to arsenic sites with zero (or three) and two As-As bonds. High Ge and As content leads to formation of microclusters, where the predominant structural units are, possibly, As4Se4 molecules or partial molecules with As-As bonds. The NQR spectrum for the composition Ge0.33As0.12Se0.55 ((r) over bar = 2.78) shows a weak peak corresponding to an arsenic site with zero (or three) homobonds and two resolved peaks in the high frequency region. Such behavior is consistent with an increase in inhomogenity in the local structure and perhaps nanoscale phase separation. (C) 2007 Elsevier B.V. All rights reserved.