Thermal expansion of a boron-doped diamond single crystal at low temperatures

The lattice parameter of a single-crystal boron-doped synthetic diamond has been measured in the range 4.2-300 K by x-ray diffraction (Bond method), with precision +/-2.0x10(-6). Over the whole range the results are consistent with a = 3.566662+4.25x10(-14)T(4) Angstrom, where T is the absolute temperature. The dilation due to doping indicates a boron concentration of about 100 ppm. The increase of thermal expansion over that of an undoped synthetic diamond is found to be unexpectedly large (10-15%), giving an apparent dilation on doping that is markedly temperature dependent.