Magnetic properties and surface resistance of Rb-doped YBaCuO ceramic

Abstract

The influence of Rb,CO,additive on the properties of YBCO was investigated. The impurity was added to the usual stoichiometry of Y,Ba,Cu,Oy to produce an initial batch with general formula Y ,Ba,Cu,(Rb)xO where x=O to 0.60. Only traces of(2.21 r102wt%)Rbwerefound~n allsamplesafterfinal baking.Adding Rb shifted the temperature T , of the "magnetic transition" towards lower temperatures without affecting the eiectricai HTSC characteristics and improved the grain size homogeneity.

Grain boundary contribution to the a.c. field behaviour of doped YBCO ceramics

“…Unfortunately, we were not able to obtain Raman spectra of the unknown phase on the grain boundaries of KCu:YBCO, as even the lowest laser power overheated the spot studied: this suggests that the phase absorbs strongly and has a low melting point. Such properties of the unknown phase are to a large extent similar to those of a KCu compound described in the literature and whose presence in the sample has been established in other investigations [3] by means of x-ray analysis.…”

“…The same approach was used in the preparation of doped YBCO specimens. We studied two types of additives known to accumulate on the grain boundaries: CuO and K 2 CO 3 which are known to react with one another during the process of YBCO preparation [3] (the samples are denoted hereafter by KCu:YBCO); Rb 2 CO 3 (Rb:YBCO [4]) which forms a liquid phase at temperatures close to the temperature of final baking and affects the recrystallization processes.…”

“…A comparison of the two structures reveals a significant rise of the boundary volume related to the internal pores in the doped sample. On the other hand, some of our earlier work [3] showed that introducing The Raman spectra were obtained with experimental equipment comprising a triple spectrometer, a multichannel analyser and a microscope. The pumping radiation was the λ = 488.0 nm line of an Ar + laser, with the power of the incident light reduced to below 9 mW to avoid the heating of the spot studied.…”

“…We report here studies of the influence of the variation of the fraction of grain boundary volume as a function of the grain size on the material's hysteretic losses and screening properties in low-frequency a.c. fields, the critical current density J c and the temperature of the superconducting transition T c . We also present an attempt to clarify the role of additives that accumulate on the grain boundaries of a YBCO polycrystal [2,3].…”