X-ray diffraction study of BaLu₂CuO₅ and BaNd₂CuO₅ at high pressures

Abstract

The volume compression of BaNd₂CuO₅ (brown phase) and BaLu₂CuO₅ (green phase) have been measured to 8.67 and 9.23 GPa, respectively, utilizing a diamond anvil high-pressure cell and energy dispersive X-ray powder diffraction. The pressure dependence of the volume of the orthorhombic BaLu₂CuO₅ and tetragonal BaNd₂CuO₅ unit cell, as determined by a least-squares fit of the data, are both linear and follow the equations of V=−1.615P+260.62 ų, and V=−1.9001P+476.92 ų, respectively. While linear compressions of the unit cell parameters of BaNd₂CuO₅ exhibit isotropic compressive behavior within our experimental error, BaLu₂CuO₅ shows somewhat anisotropic compressibility behavior. From the observed data, the bulk modulus of BaNd₂CuO₅ is determined to be 161±8 GPa and the Young's modulus is estimated to be 193 ±9 GPa. For BaLu₂CuO₅, the corresponding bulk modulus and the Young's modulus are estimated to be 251±13 GPa and 301±16 GPa, which are significantly greater than those of the brown phase and the high-T_c superconductor Ba₂YCu₃O_6+x. No evidence of a pressure-induced phase transformation was found in either compound in the pressure range studied.