Using two different high-pressure techniques, we have prepared boron-doped diamonds with atomic concentration of the dopant ranging from 0.04% to 4% (from $7\times {10}^{19}$ to $7\times {10}^{21}\mathrm{atom}∕{\mathrm{cm}}^3$) and studied the lattice constants and thermal expansion of the diamonds in the temperature range from 90 to $300\mathrm{K}$. Both sets of samples demonstrate the same increasing concentration dependence of the lattice parameter with maximum shift of the lattice constant about $0.011\mathrm{\AA }$. We have established an abnormally high thermal expansion of the heavily boron-doped superconducting diamonds with respect to the undoped ones and a nearly linear correlation between lattice constant and critical temperature of the superconducting transition.

• Received 18 September 2006

DOI:https://doi.org/10.1103/PhysRevB.74.140502