SOL-GEL SYNTHESIS AND CHARACTERIZATION OF YBa₂(Cu_1-xCr_x)₄O₈ SUPERCONDUCTOR

Giedrė Nenartavičienė, Darius Jasaitis, and Aivaras Kareiva
Department of General and Inorganic Chemistry, Vilnius University, Naugarduko 24, LT-03011 Vilnius, Lithuania

Abstract
In this study the chromium substitution effects in the YBa₂Cu₄O₈ (Y-124) superconductor has been investigated. Superconducting oxide ceramics of composition YBa₂(Cu_1-xCr_x)₄O₈ (x = 0.01; 0.03; 0.05; 0.10; 0.20) have been prepared by a simple aqueous sol–gel method using aqueous mixtures of the corresponding metal acetates and nitrates. Homogeneous precursor gels were obtained by complexing metal ions with tartaric acid. The obtained gel powders, intermediates and end products were characterized by X-ray powder diffraction analysis (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and resistivity measurements. The bulk samples were obtained after firing the precursor gels at 800 °C in flowing oxygen atmosphere. Doping the YBa₂Cu₄O₈ phase with chromium shows a strong effect on the superconducting properties decreasing the critical temperature from 78 K (for non-substituted sample) to 60 K (for the YBa₂(Cu_0.90Cr_0.10)₄O₈). Synthesis product containing 20 % chromium instead of copper showed nonsuperconducting behaviour.

Key words: chromium, sol-gel, superconductor