Effect of isotopic composition on the lattice parameter of germanium measured by x-ray backscattering

Abstract

We have measured, by x-ray backscattering, the lattice constant of four highly enriched Ge isotopes: $A=70,$ 73, 74, and 76 at temperatures ranging from 8 to 300 K. Comparing with ${}^{70}\mathrm{Ge},$ values of $\ensuremath{\Delta}a/a$ ranged from $\ensuremath{-}10$ to $\ensuremath{-}46$ p.p.m. A good quantitative agreement over the whole temperature range (8--300 K) was found with values calculated from a theory that takes into account the zero point motion and the anharmonicity of the lattice.