Preparation of CdBa2Cu3O7−δ superconducting ceramic and a study of its electrical properties

Abstract

A new superconducting ceramic material CdBa2Cu3O7−δ is obtained. It is found that the superconducting transition (at 86 K) is retained when yttrium is fully replaced by cadmium in the Y-Ba-Cu-O system. X-ray diffraction studies show that the crystalline structure is unchanged and the identified peaks coincide when Y is replaced by Cd in YBa2Cu3O7−δ. Besides a stable superconducting transition, a phase transition near 275 K was seen in the temperature dependence of the specific resistivity which shifted toward lower temperatures (252 K) and then disappeared completely over repeated measurement cycles. The thermal conductivity k of YBa2Cu3O7−δ and CdBa2Cu3O7−δ was found to vary little with temperature up to the superconducting transition. Substituting Cd for Y in the initial HTSC material led to a substantial increase in the lattice thermal conductivity. Measurements of the thermal emf showed that it is positive in YBa2Cu3O7−δ and negative in CdBa2Cu3O7−δ.

Analysis of fluctuation conductivity in Y-=SUB=-0.5-=/SUB=-Cd-=SUB=-0.5-=/SUB=-Ba-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=-

“…Polycrystalline YBa 2 Cu 3 O 7−δ and Y 0.5 Cd 0.5 Ba 2 Cu 3 O 7−δ were obtained by the method tested in [23,28]. At the first stage, the initial components in a stoichiometric ratio were mixed and annealed in air at a temperature of 1120 K for 25 h. At the second stage, the resulting compositions were annealed in an oxygen atmosphere (at a pressure of 1.2−15 atm) at a temperature of 1190 K for 25 h, then subjected to slow cooling to room temperature.…”

“…From this point of view, the compound YBa 2 Cu 3 O 7−δ (YBCO) is attractive due to the opportunity of wide variation of the composition by replacing yttrium with its isoelectronic analogs, or by changing the degree of oxygen nonstoichiometry. Note that yttrium in the composition of YBCO is easily replaced by most lanthanides and other elements [1,[21][22][23][24][25][26][27][28][29][30], which usually does not lead to deterioration of the SP properties of the initial composition. The exception is praseodymium, t. k. PrBCOdielectric [31,32].…”