COMPRESSIBILITY OF THE HGBA2CAN-1CUNO2N+2-DELTA (N=1,2,3) HIGH-TEMPERATURE SUPERCONDUCTORS

The transition temperatures (T(c)) of the homologous series HgBa2Can-1CunO2n+2+delta of high-temperature superconductors show very large (approximately 30 K) pressure enhancements, saturating at 118, 154, and 164 K for Hg1201, Hg1212, and Hg1223, respectively. We have measured the compressibility of the first three mercury superconductors in a diamond-anvil cell using energy-dispersive synchrotron x-ray diffraction. We report the tetragonal-cell parameters a and c up to 30 GPa. We find ambient-pressure bulk moduli, K(v0) = -V0(partial derivative P/partial derivative V)0, of 65.4(3.0), 91.6(4.7), and 83.8(10.5) GPa for Hg1201, Hg1212, and Hg1223, respectively. The Hg superconductors are highly compressible compared to other high-temperature superconductors which generally show bulk moduli in the range of 100-200 GPa. The relation c = A + B (n - 1) holds for the c-axis cell parameter at ambient pressure, however, the relation breaks down at high pressures.