Structure and crystal chemistry of the high-Tc superconductor YBa2Cu3O7−x

Oxides and oxide superconductors :

“…Theoretically, at T = 0 K, the Debye temperature calculated from elastic constants is exactly the same as that from specific heat [216]. [221], the perovskite crystal structures reported by Naimon [222], and the oxide-superconductor crystal structures considered by Iguchi Studying many monoxides and perovskites, Ledbetter and Lei [174] found a correlation between bulk modulus and cation-anion bond distance shown in Table 6.1 shows these bond distances given by David and coworkers [224]. Using the bond lengths in Table 6.1 together with the curve in Fig.…”

“…Zeyher and Zwicknagl [234] calculated the superconductivity-induced phonon self-energy in the strongcoupling limit and found that A = 2.9. [224] were adopted. Table 9.1 shows this information.…”

“…Besides the charge distributions, Ohta and coworkers [248] Table 7.1). The unit-cell dimensions and ionic coordinates of David and coworkers [224] were used for the Madelung-site-potential calculations. Compared with measurements [243,244], which range from negative values to 4.3 K/GPa, the result for dTc/dP falls among the lower positive values.…”

An Electron Microscope Study of Defect-free YBa2Cu3O7?x (x » 0.15) with Superconductivity at 93 K

“…It is well known that mixed-phase YBa2Cu307_x may become superconducting in the temperature range 50-106 K, the precise temperature depending upon the preparation conditions (WU et al 1987;Syono et al 1987;Strobel et al 1987;David et al 1987;Gopalakrishnan et al 1987). Much interest has centred upon the identification of the phase which has the major contribution to the superconductivity, and to its preparation as a pure phase.…”

Mixed valence and superconductivity

“…If Uz0 and H 12 /l large, electron pair transfer may occur without activation energy. Since MV-3 systems involve two electrons, a reasonable hypothesis is that MV-3 systems, fulfilling both delocalization conditions, become superconducting at low T (David 1987;Larsson 1989Larsson , 1998. MV-2 systems, involving a single electron, delocalize to ordinary metals (Larsson 2006).…”