Consequences of crystallographic equivalence between bct and fct indium

Abstract

The force-constant relations involving the elastic constants and the phonon dispersion relations for bct indium, deduced on the basis of a general tensor force (GTF) model, are compared with those for fct indium to resolve some conflicting consequences of their crystallographic equivalence. It is shown that the numerical values of the force constants of this model differ from bct indium to fct indium, whereas those of other lattice-dynamical models are invariant, but the same transformation equation relates the phonon frequencies of the former with those of the latter in all cases. Further, the relations between the GTF constants of bct indium and those of fct indium, obtained by making use of their relations with other invariant force constants reveal their correct dependence on coordinate axes. The basic differences between GTF and other models, the transformation properties of these force constants, and their link with the various manifestations of the crystallographic equivalence are discussed.