Ultrasonic investigations on superconducting YBa2Cu3O7-δ samples of different microstructure

Study on Thermal Hysteresis of Elastic Modulus in Granular Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O

“…This result has been confirmed by others [7,8]. The thermal hysteresis was ascribed to microstructure [6] or the relaxation of thermoelastic stress caused by the anisotropy of the thermal expansion of grains [71, instead of phase transitions. In this paper, firstly, the elastic constant C has been measured for the single crystal of Bi 2 Sr 2 C aCu 2 0 8 to clarify if Re thermal hysteresis occurs and if exists, how large it is.…”

“…An AC-cut quartz transducer with area 1.5x4 mm2 was bonded to the a-c plane, so that the shear strain ( e 2 1 ) waves propagated along the baxis, and then C 6 and 100 K has been studied with ultrasonic longitudinal waves propagated along b-axis. An AC-cut quartz transducer with area 1.5x4 mm2 was bonded to the a-c plane, so that the shear strain ( e 2 1 ) waves propagated along the baxis, and then C 6 and 100 K has been studied with ultrasonic longitudinal waves propagated along b-axis.…”

Elastic behaviour under pressure of high-T c superconductors RBa2Cu3O7-x (R = Y, Gd and Eu)

“…Previous ultrasonic studies of YBa,Cu,O, -x at atmospheric pressure (Almond, Lambson, Saunders and Wang Hong 1987a, b, Lang et al 1987, Yening, Huimin, Jinsong, Ziran, Min, Zhongmin and Zhifang 1987, Bishop, Gammel, Ramirez, Cava, Batlogg and Rietman 1987a, Bishop, Ramirez, Gammel, Batlogg, Rietman, Cava and Millis 1987b, Yusheng, Baiwen, Sihan, Jiong, Yongming and Haming 1987, Horie, Fukami and Mase 1987, Jericho, Simpson, Tarascon, Green, McKinnin and Hall 1987, Ewert et al 1987) have revealed considerable sample to sample variations and in some cases extensive thermal hysteresis of ultrasonic wave velocities in this ceramic of highly variable microstructural properties including density, pore and grain size and oxygen content. Here we report the first measurements of the effects of hydrostatic pressure on the longitudinal and transverse ultrasonic wave velocities in polycrystalline ceramic specimens of YBa,Cu,O, -x, GdBa,Cu,O, -x and EuBa,Cu,O, -X.…”

Role of Internal Stresses in Electronic Pairing of Layered Superconductors

“…Now we can use the experimental data for the relative change of the sound speed in the crystal at a given temperature (see [16]) to estimate " u = 0.026 to 0.040. From (30) we obtain for the hole-deformation coupling constant l " u t n 2…”

“…It follows from the preceeding expressions that l j j V 0 b % 2 ÁW stress V 0 aDV 0 2 ÁW stress a" u, where ÁW stress is the change in the band width caused by stress. For " u we estimated values of 0.026 to 0.040 (see [16]). With |l| = 6.68 eV this gives W stress = 0.087 to 0.134 eV.…”