Hydrogen occupancy, 1H NMR spectrum and second moment of Zr xNi 1− x–H metallic glasses

Abstract

The paper presents the results of an experimental investigation of rigid-lattice proton magnetic resonance (PMR) spectra and second moments in Ni 0.67Zr 0.33–H, Ni 0.50Zr 0.50–H, Ni 0.33Zr 0.67–H binary glassy alloy–hydrogen systems in the range of hydrogen-per-metal ( H/ M) ratio of 0.14≤ H/ M≤1.9. The line shape can be described by the empirical Harper-Barnes function with exponent values ranging from 1.45 to 2.95 in the whole hydrogen concentration range. The generally assumed Gaussian form is valid in a narrow H/ M interval only. The second moment as a function of H/ M can be fitted by a power function of an exponent 3/4. The exponent is independent of the composition of the alloy. We found that a simple lattice gas model based on a homogeneous hydrogen distribution contradicts the experimental results. Instead, a short-range order model has been proposed in which the hydrogen atoms are located in the centres of distorted tetrahedra of metal atoms, that is in the basic building blocks of the amorphous alloys. The Switendick criterion was also taken into consideration. We have shown that few proton first neighbours (0–2) and a small number of second neighbours (1–8), that is, a cluster of hydrogen is sufficient to account for the measured value of the second moment. Ternary Zr 0.5Ni 0.5− x Cu x –H alloys have been investigated, too. The addition of Cu nuclei did not lead to the second moment enhancement expected for a homogeneous distribution of components.