Abstract
To shed further light on outstanding problems associated with the magnitude of the bulk modulus and its pressure dependence in high-{ital T}{sub {ital c}} superconductors, a comparative study has been made of the effects of hydrostatic pressure on the elastic properties of ceramic specimens of the electron-doped Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}{ital y}} and the hole-doped La{sub 1.8}Sr{sub 0.2}CuO{sub 4} superconductors and their nonsuperconducting parent compounds Nd{sub 2}CuO{sub 4{minus}{ital y}} and La{sub 2}CuO{sub 4}. The effects of porosity on the elastic properties have been taken into account by use of wave-scattering theory in a porous medium. The ultrasonic-wave velocities and bulk modulus {ital B}{sub 0} measured in the polycrystalline La{sub 2}CuO{sub 4} are in reasonable agreement with those determined from elastic-constant measurements in single-crystal La{sub 2}CuO{sub 4}. This observation lends strong support to the suggestion that for these mixed oxide ceramics the true bulk modulus at atmospheric pressure is the one {ital B}{sub 0} derived from ultrasonic measurements rather than that {ital B}{sup {ital T}}({ital P}) obtained from x-ray experiments at very high pressures.
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