Isotopic dependence of the lattice constant of diamond

Abstract

We report measurements of lattice constants of single-crystal synthetic diamonds that cover the range of isotopic compositions from almost-pure $^{12}\mathrm{C}$ to almost-pure $^{13}\mathrm{C}$. These provide a demonstration of an effect of isotopic composition on the lattice constant of this material. The results are consistent with a linear dependence ${\mathit{a}}_{0}$(C,25 \ifmmode^\circ\else\textdegree\fi{}C,x)=3.567 15-0.000 53x \AA{}, where x is the atom fraction of $^{13}\mathrm{C}$. This corresponds to a fractional change between the end compositions of \ensuremath{\Delta}${\mathit{a}}_{0}$/${\mathit{a}}_{0}$=-1.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$, which is less than the smallest value in a range of theoretical estimates that have been published previously. The synthetic diamonds yielded (400) Bragg peaks with widths in the range 12--17 arc sec that are not perceptibly dependent on the isotopic composition.