Synthesis of superconducting boron-doped diamond compacts with high elastic moduli and thermal stability

Polycrystalline bulk compacts (3.5-4.0 mm in diameter and 2.5 mm in height) of superconducting boron-doped diamond with high elastic moduli have been synthesized from mixtures of graphite and boron carbide at pressures 8-9 GPa and temperature of 2500 K. We show that graphite-to-diamond transformation in the presence of liquid boron-carbon growth medium leads to formation of polycrystalline diamond matrix at B4C concentration in the initial mixture ranging from 3.5 to 5%. Resistive transition of the samples to the superconducting state starts at 4 K and ends at 2.2 K. The thermal conductivity of the samples slightly increases in the temperature range of 230 to 400 K, and at room temperature it is as low as similar to 0.4 W/cm K. The boron-doped diamond demonstrates very high oxidation resistance up to 1200 K, and can be used as electrical structural material that can be exploited at elevated temperatures in air. (C) 2014 Elsevier B.V. All rights reserved.