Structure and superconductivity for YBa2Cu3O7-Agx

Infrared Spectroscopy and Raman Spectroscopy Evidences of Silver Replacement into Cu (1) Site in YBa₂Cu₄O₈

“…Force constant can be estimated from bonding energy, interatomic distance and the potential formu la. Interatomic distances and bonding energies of Cu(1)-(4), Cu(2)- (4) and Ag(1)-(4) are necessary. Cu-bonding energy of Cu2 is about 930eV and interatomic distance is about 0.184nm, and Ag-bonding energy of Ag2 is about 370eV and interatomic distance is about 0.205nm.28) Cu(1) (4) distance is 0.183nm and Cu(2)-(4) distance is 0.229nm,18) and we assume that Cu(1)(4) bonding energy is 930eV and Ag(1)- (4) bonding energy is 370eV.…”

“…Cu (1) is defined in the next chapter. Kolesov et al have also reported a silver replacement into the Cu (1) site in the 123 phase, and proved it by Raman scattering method.10) Ren et al 4) and Choy et al) have report ed further the substitution by X-ray diffraction method and lattice parameter measurements. But there has been no work reported on YBa2Cu4O8 (124 phase).…”

“…Crystal structure of the 124 phase has been studied well by Wright and Butler.18) The nearest atom to Cu (1) in the 124 phase is oxygen atom called O(4) (Cu(1)-O(4) dis tance is 0.183nm), and the next one is also oxygen atom called O (1) (Cu(1)-O(1) distance is 0.194nm).18) It has been reported that the doped sil ver atoms substitute with Cu (1) in the 123 phase. As suming that silver atoms subsitute also with Cu (1) in the 124 phase, the study of Cu(1)-O (4) and Cu(1)-O(1) vibrations will demonstrate an evidence to clarify whether silver atoms can replace copper atoms of the Cu 1 This law holds in C-N, C-, P-S and Si-H systems.19), 20) An Ag-bond with a length of 0.2043nm in Ag2 has a strong IR absorption peak at 540cm-1.21) According to the kd3=const. law, the constant is calculated as kd3=540(0.2043)3= 4.6.9 Assuming that a silver atom enters into the Cu(1) site of the 123 phase, the interatomic distance between silver and oxygen can be estimated as 0.19 nm and the IR absorption wavenumber is calculated as k=670cm-1.…”

Flux dynamics of YBCO/Ag composite

“…It was reported that addition of silver reduces the normal state resistivity (Dwir et al 1989;Sen et al 1989) and enhances the transport critical current density in YBCO (up to 30 Wt~o of Ag) by a factor of 2-3, measured at 77 K under zero applied magnetic field (Jung et al 1990;Dhingra et al 1991). The mechanical properties also improved with the addition of silver (Singh et al 1989;Ren et al 1990). Silver causes significant grain growth with better intergranular connectivity through partial melting of YBCO (Tiefel et al 1988;Baliga and Jain 1989).…”