Experimental gradient elastic tensors: Measurement in I-VII semiconductors and the ionic contribution in III-V and I-VII compounds

Abstract

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.