Nuclear-acoustic-resonance measurements have determined the magnitudes and relative signs of the two nonzero tensor components, $S_{11}$ and $S_{44}$, of the tensor $S$ which relates elastic strain to electric field gradients at a nuclear position of ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$, ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$${}_{}{}^{79}{}_{}{}^{}\mathrm{Br}$, and ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$. The measured magnitudes of $S_{11}$ in these I-VII compounds and in seven III-V compounds are shown to agree with calculated values of an ion-charge model based on free-atom values. Such agreement is found if ion charges characteristic of covalent bonding are used for the III-V compounds and ion charges characteristic of ionic bonding are used for I-VII compounds.

• Received 2 February 1976

DOI:https://doi.org/10.1103/PhysRevB.13.4504