Nuclear Quadrupole Resonance and the Electric Field Gradient in Metallic Indium

Abstract

The nuclear quadrupole resonance in metallic indium has been followed continuously from 4.2\ifmmode^\circ\else\textdegree\fi{}K to 390.2\ifmmode^\circ\else\textdegree\fi{}K and two sources of field gradient have been investigated. One of these is the usual "ionic" model involving point ions in a uniform background charge density. The contribution from this source has been calculated by a new method to seven figures at three representative $\frac{a}{c}$ ratios; from these data the ionic field gradient in indium at any submelting temperature can be inferred.Since the ionic contribution accounts for only about 20% of the observed field gradient, a second source has been considered. This source is an undulatory component of charge density having the periodicity of the lattice. It is found that a modest amount of this undulatory component does produce sufficient field gradient to explain the observations.