ON Zr SUBSTITUTION IN T′-TYPE Nd–Ce–Cu–O SYSTEM

Abstract

The effect of tetravalent Zr substitution (≤2 at%) at the Cu site in T′-type Nd 2-x Ce x CuO 4-δ (NCCO), x = 0.12, 0.14, 0.15, on the superconducting (SC) behavior is investigated. EDX analyses of the samples clearly reveal the presence of only ~0.5 at% Zr in the T′-phase. Irrespective of the Ce content (0.12 ≤ x ≤ 0.15), T c is found to depress with Zr. A fall in T c of ~2 K is observed due to 0.5 at% Zr 4+ in x = 0.14 samples, while the NCCO (x = 0.12) on substitution of Zr (expected to dope 2 electrons per Zr 4+ and induce superconductivity) remains non-SC. The reported conjecture regarding T c inducement due to the carrier addition of 0.03 (per formula unit) arising from 3 at% In 3+ (or Ga 3+) substitution for Cu in Nd 1.88 Ce 0.12 CuO 4-δ [Ayoub et al., PhysicaC170, 211 (1990); Felner et al., Phys. Rev.B40, 11366 (1989)] is not applicable for the Zr-substituted NCCO.