High-quality ceramics of YBa₂Cu₄O₈ from citrate sol-gel precursors sintered at one atmosphere oxygen pressure

Single phase ceramic material of the superconducting phase YBa₂Cu₄O₈ has been synthesized at 780-790°C under one atmosphere oxygen pressure with a sol-gel powder precursor technique. The precursor was derived from citrate metal ion complexes uniformly dispersed in a solvent mixture of ethyleneglycol and water. The main advantages of the present method are, apart from the low oxygen pressure needed, the elimination of centrifugation, ageing and fine control of pH usually required for other solution techniques. X-ray diffraction analysis show that the material is virtually of single-phase character with only minor traces of CuO (∼1%). AC-susceptibility measurements indicate a high-quality sample with an onset of the superconducting transition at T_c=82.6 K. The superconducting transition is much sharper, ΔT_c(10-90%)=4.5K, than for ceramic samples of previously reported synthesis procedures.