The nuclear quadrupole interaction at inequivalent lattice sites in ammonium paramolybdate: A TDPAC study

A nuclear quadrupole interaction (NQI) study using the time differential perturbed angular correlation (TDPAC) technique on ammonium paramolybdate (APM) has shown three inequivalent molybdenum sites in this compound which consists of seven MoO6 polyhedra connected through edges. In this study the nuclear probe 99Mo was used to measure the γ-γ perturbed angular correlation of 99Tc on Mo-sites to obtain the quadrupole interaction parameters. The quadrupole interaction frequencies (ωQ) for the three sites are 0.0224, 0.0386 and 0.0434 rad/ns and the asymmetry parameters (η) of the electric field gradient (EFG) are 0.45, 0.18, and 0.58, respectively. The site assignment is based on the population ratios 4:2:1. The Mo atoms with the highest population show the lowest ωQ indicating that this set of polyhedra is “least” distorted or condensed. Besides the least squares fit, a cross-correlation algorithm has been used to analyze the experimental data to corroborate the fitted parameters and quoted errors. The derived NQI-parameters can be used for site assignments in other compounds built from condensed Mo-O octahedra.