Growth and superconducting properties of(Eu,R)Ba2Cu3O7−δ (R = Er,Tm) single-crystalline whiskers

Abstract

We have grown single-crystalline whiskers of superconducting (Eu, R)-123(R = Er,Tm), systematically changing the ionic radius by means of doping with Er or Tm, whichhave smaller ionic radii, in place of Eu. We tried to gain an understanding of the oxidation,doping and superconducting state of the materials by annealing whiskers at differentconditions, studying the temperature dependence of the magnetization and carrying outx-ray diffraction analysis and quantitative electron probe microanalysis measurements. Weobserved that Eu-rich whiskers, which require higher temperature for growth, are moreliable to have oxygen deficiencies and structural instabilities. Upon Er or Tm doping boththe oxygen deficiency and the substitution of rare-earth elements at the Ba site decrease.Our results show that the carrier doping can be systematically controlled, fromthe highly underdoped to the slightly overdoped range, by making a suitablechoice of the ionic radius of the rare-earth elements in the as-grown whiskers.