Superconductivity in the (Yba₂Cu₃)_1−xNa_xO_7−δ System

Abstract

The (YBa,Cu,),-,Na,O,-, system in the range of x = 0 4 . 8 was investigated. Experimental data suggest that the sodium doping with x I 0.26 does not affect the critical transition temperature T,, and the crystal structure maintains the orthorhombic lattice with a slightly smaller unit cell. However, sodium doping increases the sintering and grain growth kinetics, resulting in a higher superconducting phase volume and an enhanced Meissner effect. It also lowers the processing temperature. The experimental data also suggest that the sodium atoms diffuse into the superconducting YBa,Cu,O,-, crystallites, which stabilizes the orthorhombic phase. The transition temperature (orthorhombic to tetragonal) in sodium-doped materials increases with the increasing concentration of sodium.

Microstructure, magnetization and dc transport properties of MTG-YBa1.8Na0.2Cu3Oycrystal

“…Although the effect of YBCO superconducting materials by alkali-metal elements has been reported in polycrystal samples [6][7][8][9][10], there is no solid evidence to support the Na ion in the Y123 cell. In order to obtain evidence that the Ba site or the Y-site is replaced by an Na ion, we have determined the composition of the crystal on the cross section.…”

“…YBCO. A special interest is associated with doping of YBCO superconducting materials by alkali-metal elements, which improve the oriented grain growth [6], the oxygen diffusion [7] and the superconducting properties [8][9][10]. Recently, Zou et al [11,12] have studied the effect of Na addition on the T c , J c properties of melt-textured-growth MTG-YBCO and found that with certain Na addition, MTG-YBCO showed an improved critical current density characteristic and a second peak in the magnetization curves.…”