Structure-compressibility relationships in layered cuprate materials

High-resolution synchrotron x-ray powder-diffraction experiments have been undertaken on the related series of layered cuprates of chemical formula HgBa₂CuO_4+δ, Hg_0.8Cr_0.2Ba₂CuO_4+δ, Sr₂CuO₂CO₃, NbSr₂EuCu₂O₈, GaSr₂YCu₂O₇, and Pb₂Sr₂YCu₃O_8+δ to applied pressures of 6.05, 7.64, 5.56, 4.47, 6.00, and 6.03 GPa, respectively. No discernible structural phase transitions were observed over these pressure ranges. The data have been analyzed using the Murnaghan formula to derive compressibilities and bulk moduli. The ambient pressure bulk moduli for the various cuprates are 63(2), 64(2), 62(2), 120(4), 85(3), and 129(4) GPa, respectively. In all cases the compressibility is the highest in the direction perpendicular to the cuprate layers (out-of-plane) and very anisotropic, with ratios for the out-of-plane to the in-plane compressibilities of 1.38, 1.25, 1.97, 1.45, 1.37 and 3.31, respectively. These variations are discussed in light of the crystal chemistry of these systems, and the observed trends should be helpful in tailoring the response of layered cuprates to applied hydrostatic pressure.