A mechanical spectrum study of bilayer cuprate La1.82Sr0.18CaCu2O6+δ

The mechanical spectrum of bilayer cuprate La_1.82Sr_0.18CaCu₂O_6+δ (La2126) was measured using the vibrating reed method from 30 K to room temperature at kilohertz frequency. A clear modulus softening was observed at 223 K accompanied by a sharp internal friction peak, which evidences a phase transition. Another broad internal friction peak around 250 K was observed, accompanied by a large modulus change. This contrasts with the broad internal friction peak of Ca doped Y Ba₂Cu₃O_7−δ (Y123) for which no clear modulus change was observed. The main contribution to the broad internal friction peak of La2126 is expected to be from the glass transition of the interstitial oxygen atoms.