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The internal friction of partially Sr-substituted Y(Ba 1−x Sr x ) 2 Cu 3 O 7−δ (Y123) ceramics was measured by the vibrating-reed method from liquid nitrogen temperature to room temperature at kilohertz frequencies. The intensity of the internal friction peak, which appears around 220 K, decreases upon Sr doping while the peak position shows no systematic change. Our results do not support the previous oxygen order-disorder explanation; we present another approach relating this peak to the crossover in charge-carrier dynamics, and its evolution with Sr doping is discussed in terms of release of internal strain and electron-phonon coupling.

A new experimental method describing the determination of the mechanical spectra (complex Young’s modulus Y*=Y′+iY″ versus temperature) of materials from the liquid to the glassy state, including the glass transition, is reported. The conventional vibration-reed method developed for solids is extended to composite systems consisting of a reed substrate and a deposited material. Mathematical expressions for the evaluation of the mechanical spectrum of the deposited material are obtained by solving either directly the vibrating equation of the nonuniform reed, or that of an equivalent uniform reed, with new length and stiffness, using a coordinate transformation. The mechanical spectra of glycerol and 1,2-propanediol carbonate covering the liquid and the glassy state are presented as examples in this work. The glass transitions of these two kinds of materials, as well as the recrystallization, melting and, evaporation processes of 1,2-propanediol carbonate, are identified in the respective spectra.

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