X-ray diffraction study of HgBa₂CuO_4+δ at high pressures

An in situ high pressure study using energy dispersive X-ray diffraction has been carried out on the polycrystalline high-T_c superconductor, HgBa₂CuO_4+δ (Hg-1201), to study its phase stability under pressure and also to measure its compressibility and bulk modulus. No evidence of pressure-induced polymorphism was found in the pressure range investigated, i.e., from 0.1 MPa (1 atm) to 5 GPa. The compound exhibited anisotropic elastic properties. The axial compressibility along the c axis was measured to be (3.96 ± 0.35) × 10^-3 GPa^-1 and along the a axis (3.42± 0.13) × 10^-3 GPa^-1, corresponding to an anisotropy ratio of 1.16 ± 0.11. The bulk modulus was determined to be (94.7 ± 4.2) GPa and, assuming a Poisson's ratio of 0.2, Young's modulus was estimated to be (170 ± 8) GPa.