Growth and characterization of (Y, Pr)-123 single crystals: influence of Al contamination and post-annealing under oxygen pressure

Abstract

(Y 1− x Pr x )Ba 2Cu 3− z Al z O 7−δ (0 ≤ x ≤ 1) single crystals of large surface area (up to 9 × 8 mm 2) and thickness between 0.3 and 1.5 mm were grown in Al 2O 3 crucibles using a self-flux method. The crystals were characterized by means of AC susceptibility, X-ray diffraction, energy dispersive X-ray spectrometry, optical reflectance measurements and Raman spectroscopy. To ensure that the crystals are fully oxygenated, post-annealing of the crystals was performed under high oxygen pressure (100–200 bar) in a home-made autoclave. With increasing Pr content a strong reduction of T c, a softening of the Raman B 1g mode, a hardening of the Raman A 1g mode, a red shift of the plasma edge and a strong decrease of the in-plane optical conductivity in the infra-red region were observed. The Raman data indicate that the valency of Pr is close to +3. EDX measurements as well as Raman measurements show, that the Al contamination of the crystals (which results from crucible corrosion) increases with increasing Pr content. The complete disappearance of the free carrier concentration which was determined by optical reflectivity measurements is affected by the Al contamination.