THERMAL-EXPANSION OF SYNTHETIC DIAMOND SINGLE-CRYSTALS AT LOW-TEMPERATURES

The thermal expansion of the lattice parameter of synthetic diamond single crystals has been measured in the range 4.2-320 K by the Bond method. The thermal expansion coefficient calculated from the experimental results is very small (of the order of 10(-7) or less) and no definite evidence of negative thermal expansion is found within our relative experimental accuracy of the order of +/-1 X 10(-6). We measured the temperature dependence of the lattice parameter of the synthetic diamond single crystals irradiated by high energy accelerated heavy ions, but its thermal expansion behaviour does not show a marked change.