Elasticity of diamond under pressure to determine an absolute pressure scale

Diamond’s remarkable hardness and its cubic structure make it an ideal material for determining a universal pressure scale. As such, it has been chosen as the reference for the International Practical Pressure Scale (IPPS) gauge for ruby fluorescence, one of the most widely used pressure calibrants for experimentation in diamond anvil cell [1]. However, the theoretically calculated value of the bulk modulus pressure derivative B’₀= (dB/dP)_P=0 currently adopted [1] lacks a direct experimental validation [1].

The value of B’₀ can be easily derived once all the independent elements of the elastic tensor of diamond under pressure are known, but such measurements are very challenging as the high value of B₀ implies very precise determinations over and extended pressure range, and for the most commonly used techniques the signal from the diamond sample is masked by the huge signal from the anvils of the high-pressure apparatus [2,3].



Here, I will present high-pressure sound velocity measurements on single-crystal diamonds of different orientations using a time-resolved optical pump-probe technique [4] capable of overcoming the above-mentioned difficulties. The results obtained up to about 10 GPa represent a significant step forward since McSkimin's pioneering work in the 1970s [5].



[1] Shen G. et al., HPR 40(3) 299-314 (2020)

[2] Occelli F. et al., Nat. Mat. 2 151–154 (2003)

[3] Hu Q. et al., PNAS 118 (51) e2118490118 (2021)

[4] Boccato S. et al., Phys. Chem. of Min. 49 20 (2022)

[5] McSkimin H. J. et al., JAP, 43 3 (1972)