Brillouin scattering and x-ray diffraction of solid argon to 65 GPa and 700 K: Shear strength of argon at HP/HT

We performed simultaneous Brillouin scattering and x-ray diffraction measurements on solid argon at high pressures and high temperatures (HP/HT) in an externally heated diamond-anvil cell. From the measured acoustic velocities and densities, we derive the bulk elastic properties of solid argon up to 700 K at above 60 GPa. Our measured acoustic velocity results at room temperature are in agreement with previous Brillouin scattering results. However, the derived aggregate elastic moduli differ from previous studies. In particular, the shear modulus is significantly lower. Our HP-/HT-data show that the bulk modulus is almost insensitive to an increase of temperature (within the P-T-range of our study), whereas the shear modulus G measurably decreases with increasing temperature. We find that G(P,T) can be described by a polynomial of the form: G (P,T) = 5.8(9) GPa + 1.45(12)*(P − P0) – 0.007(2) GPa−1*(P − P0)2 – 0.01(.3) GPaK−1*(T − T0) – 0.0006(2) K−1*(P − P0)*(T − T0) (where the reference P/T-conditions are 4.3 GPa and 300 K). We use our results to estimate the shear strength of argon at HP/HT, which we find to be 0.8 GPa at 65 GPa, substantially lower than found in a previous study. Increasing temperature to 700 K reduces the shear strength to 0.5 GPa at 65 GPa.