Lattice parameters and thermal expansion of superconducting boron-doped diamonds

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 7x10(19) to 7x10(21) atom/cm(3)) and studied the lattice constants and thermal expansion of the diamonds in the temperature range from 90 to 300 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 A. 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.