Single-crystal whiskers of R1Ba2Cu3Ox (R-123, R= La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) phase have been successfully grown by the Te- and Ca-doping method. The whiskers were grown from precursor pellets at just below their partial melting (peritectic) temperatures. The nominal composition of the R-123 whiskers is R1+uBa2+vCawCu3Ox (u+v+w=0, w>0) with R and/or Ba sites being substituted by Ca. However, the amount of Te was less than the analytical limit. The critical temperatures of the R-123 whiskers were around 80 K, and among these whiskers those with larger R ionic radii such as Dy, Gd, Eu and Sm require post-annealing in an oxygen atmosphere.Comment: R1Ba2Cu3O7-d, whisker, R ionic radius, crystal growth, Ca including R-123 phase, critical temperature, composition. To be published in Jpn. J. Appl. Phy

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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, which have 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 different conditions, studying the temperature dependence of the magnetization and carrying out x-ray diffraction analysis and quantitative electron probe microanalysis measurements. We observed that Eu-rich whiskers, which require higher temperature for growth, are more liable to have oxygen deficiencies and structural instabilities. Upon Er or Tm doping both the 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, from the highly underdoped to the slightly overdoped range, by making a suitable choice of the ionic radius of the rare-earth elements in the as-grown whiskers.

Single-crystal whiskers of Eu-123 were grown from Te and Ca doped precursor pellets. The Eu-123 whiskers contained a certain amount of Ca but were not contaminated with Te. Our composition analysis and superconducting property measurements reveal that the whiskers inherited certain site disorders and oxygen deficiencies in the as-grown state, which is reflected in the very low T c . High pressure oxygen annealing was required to increase the T c to about the 80 K level. Submicron sized junctions fabricated by focused ion-beam etching showed clear multi-branch structure with hysteresis in the I -V curve. The Eu-123 whiskers were found to possess excellent crystalline quality both in the as-grown state and after high pressure annealing, despite the site disorders. The critical current density J c of a Eu-123 whisker (T c = 45 K) was estimated to be 1.43 × 10 5 A cm −2 at 4.2 K, twice that observed for Y-123 having a similar T c .