An improved technique for the fabrication of thallium-based superconducting oxides, and particularly Tl:Ba:Ca:Cu:O 2223 oxides, is described which allows production of very pure superconductors (\u3e95% 2223 phase) having excellent structural characteristics. The method of the invention involves first forming a self-sustaining body of starting oxides and subjecting this body to a sintering technique wherein the temperature of the body is gradually raised to a maximum level of about 850°-930° C, followed by maintaining the body at this temperature for a period of about 48 hours. The body is then slowly cooled to avoid distortion and loss of superconducting character. Most preferably, the sintering is a two-stage operation, where the body is first heated at a relatively low rate (e.g., 1°-10° C/min.) to a temperature of about 650°-750° C, followed by faster heating at a higher rate to achieve the maximum sintering temperature. Cooling is likewise staged, involving slow cooling at a rate of about 0.1°-5° C/min. until a temperature of about 600°-650° C is reached. The body is maintained at this temperature for about 5-20 hours. Final cooling is allowed to occur naturally down to ambient temperature
