Elastic properties of superconducting Pb(1+x)/2Cu(1−x)/2(Sr1−yCay)2(Y1−xCax)Cu2O7+δ

Abstract

Using a vibrating reed technique, internal friction (Q−1) and Young's-modulus sound velocity (VE) were measured for polycrystalline samples of two types of superconducting Pb0.75Cu0.25(Sr0.9Ca0.1)2(Y0.5Ca0.5)Cu2O7+δ (Tc = 58 and 48 K) and insulating Pb0.5Cu0.5Sr2YCu2O7 in the temperature range between 30 and 300 K. For each of the samples, a broad peak was observed at 180 K in the Q−1 vs. T curve. For superconducting sampls, VE increased monotonically with lowering temperature. Moreover, there appeared to be a distinct change in slope of VE (dVE/dT) around 230 K. For an insulating sample, as temperature lowered, VE increased monotonically without any obvious change in dVE/dT. Furthermore, it was found that the temperature dependence of the magnitude of slope (−dVE/dT) was akin to that of Q−1 for each sample. These behaviors were thought to be attributable to collective displacements of oxygen atoms and/or Pb and Cu atoms in the (Pb,Cu)-O plane.