Anomalous Behavior of the Elastic Characteristics of YBa2Cu3O7 Near Tc

Anharmonic Effects in the Thermal Diffuse Scattering of X‐Rays

“…The compressibility and sound velocities and the thermal expansion coefficient have been taken from [19] and [20], respectively. We have used these data corresponding to YBa,Cu,O, -6 crystals with different compositions because of the absence of others.…”

“…The delta-functions 6(0 -ma) and 6(w + w, ) ensure that the energy is conserved in the one-phonon scattering of neutrons (the positive sign refers to phonon creation and the negative sign to phonon annihilation). Expression (19) gives the intensity of one-phonon scattering of X-rays after replacing b, by& and integrating in (18) under the condition k , -+ k,. As in X-ray scattering the major contribution to I , is due to the low-frequency acoustic phonons.…”

“…The delta-functions 6(w f w,) in (19) transform to the Lorentz functions which are then distorted by the interference between the one-and many-phonon scattering processes. For this reason it is non-trivial problem to carry out the sum over all phonon states in (19).…”

“…The delta-functions 6(w f w,) in (19) transform to the Lorentz functions which are then distorted by the interference between the one-and many-phonon scattering processes. For this reason it is non-trivial problem to carry out the sum over all phonon states in (19). This problem is not yet properly developed, however, it is clear that for X-rays and neutrons the TDS natures are different and this results in different manifestations of anharmonicity in the two methods.…”

Oxides and oxide superconductors :

“…Using a rigid-shell model with Coulomb and short-range central-force interaction, Achar,9 Barsch, and Cross [38,39] [62,68,69,79,85,95,120,166]; specific heat [73,95,159,[162][163][164][165]; temperature dependence of ultrasonic frequency [59,76,106,139,143,[145][146][147][148][149][167][168][169]. Among these studies, only thirteen papers reported the single-crystal properties of YBCO [93,[109][110][111][112][113][114][115][169][170][171][172][173].…”