Phone: þ994 12 439 35 28, Fax: þ994 12 447 04 56We have used high magnetic fields to perform 75 As nuclear magnetic resonance (NMR) relaxation measurements in Ge-As-Se glasses. The spin-lattice relaxation time T 1 has been studied as a function of average coordination number, hri and temperature, T. We show that the relaxation time constant, T 1 , in this system can be a useful tool to probe rigidity of the glassy matrix. In the two extreme cases, zero-field nuclear quadrupole resonance (NQR) and high-field NMR, T 1 exhibits a similar dependence on the average coordination number. Namely, there is a region in this dependence at low hri values, where the spinlattice relaxation time does not change remarkably, followed by an increase in T 1 in glasses with hri more than 2.54. This transition can be correlated with the onset of rigidity percolation in the glassy matrix. The temperature dependence of the spinlattice relaxation rate is found in the form T À1 1 / T 2 . This behavior is typical for As and other nuclei in glasses at temperatures below 300 K and is indicative of Raman-like relaxation mechanism involving low-frequency modes. Spinecho intensity for Ge 2 As 2 Se 5 as a function of pulse separation exhibits exponential decay whose slope is the same as one of the average of the decay found from 75 As NQR measurements. This result indicates to the presence of indirect dipolar coupling of arsenic atoms in this composition.
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