Synthesis of C_xSr₂Ca₂Cu₃O_z Superconductor from Sr₂Ca₂Cu₃O_y Precursor

Abstract

A novel compound was derived by annealing a high-pressure-synthesized sample of Sr2Ca2Cu3O y at 350 °C for 30 min in air. Energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy indicated that the composition of Sr, Ca, and Cu was not changed from the original material, and the C-K edge energy-loss near-edge structure was similar to that of CaCO3. Structure analysis revealed that this compound has a primitive tetragonal unit cell with a=3.88(3) and c=14.13(2) Å. It is likely that carbonate is incorporated either from air or secondary-phase grains into the pristine structure and forms the C x Sr2Ca2Cu3O z compound during annealing. Magnetization measurements revealed superconductivity with T conset=89 K.

Synthesis of CxSr2Ca( n −1)CunOz superconductors using high-pressure-synthesized Sr2Ca( n −1)CunOy precursors (n = 2, 4)

“…The result indicates that the 0 (Sr) 212 and 0 (Sr) 234 phase allows the partial replacement of Ca with Sr as well as in the case of n = 3. 34) These results indicate that Ca site can be substituted for Sr within the 02(n ¹ 1)n series because of the small difference in the ionic radius of Sr 2+ and Ca 2+ . After annealing, the difference in the cation ratios were limited compared from the high-pressure-synthesized sample.…”

“…This is the reason why the chemical stability of the derivative phase is higher than the original material. 34) The TEM-EDX results are presented in Table I. The Sr/ Ca ratios of two phases deviate from the ideal ratios despite the good agreement between the observed Cu/(Sr + Ca) ratios and the calculated ratios.…”

“…6) After anneal process, the critical onset temperature changes to about 91 and 65 K. The former transition corresponds that of the derivatives from 0 (Sr) 223 phase. 34) Hence, the derivative phase from the 0 (Sr) 234 phase shows T c,onset = 65 K. The volume fractions of superconducting phase in the as-prepared samples and the annealed sample were estimated to be 41 and 36% from the susceptibility at 5 K, respectively. The broadness of the transition was seem in order to exist some stacking faults in a 0 (Sr) 234 grain as we have mentioned before.…”

“…The synthetic procedure to obtain the precursors was described in detail elsewhere. 34) In the second step, the high-pressure synthesis was conducted in order to obtain the Sr 2 Ca (n¹1) Cu n O y precursors. The SrCuO 2 , Ca 2 CuO 3 , and SrO 2 precursors and a CuO powder were mixed with nominal compositions of Sr : Ca : Cu : O = 5 : 1 : 4 : 12 and 2 : 2 : 3 : 8 for the 0 (Sr) 212 phase and the 0 (Sr) 234 phase, respectively.…”

“…33) Recently, we have proposed a new method, which utilizes the metastable 0 (Sr) 2(n ¹ 1)n and 0 (Ba) 2(n ¹ 1)n phase as precursors for forming novel layered cuprate supercoductors at a very low temperature and ambient pressure by means of controlling atmosphere around these materials. 34) As an example, the novel phase change from the 0 (Sr) 223 phase was confirmed by annealed at 350 °C in ambient atmosphere. The structure of the derivative phase are proposed to be C-m223 (m Ä 1).…”