Papers by Author: Dagmar Sýkorová

Abstract: Superconductive ceramics with nominal composition Bi3.2Pb0.8Sr4Ca5Cu7Ox were prepared by solid state synthesis with 10 wt% of nanopowdered silver and were compared with those prepared by sol-gel method. The "in situ" polymerization route with citric acid and ethylene glycol was used to enhance homogeneity of the reaction mixture. The quality of samples was characterized by X-ray analysis, scanning electronic microscopy and the measurement of porosity. The superconducting properties were investigated by the measurement of the temperature dependence of magnetic susceptibility and by current voltage characteristic. All samples have critical temperatures in the range from 109 to112 K. Addition of silver always increases the volume of Bi-2223 phase and critical current density of the samples. Sol-gel samples reveal lower porosity, higher bulk density and better connectivity of the grains, resulting in the further enhancement of critical current density.

Abstract: The phase evolution and properties of strontium vanadate Sr3V2O8 were investigated using different method of preparation: solid state reaction and two wet-route techniques (colloidal route and sol-gel method - polymerized complex route). DTA/TG study showed decomposition temperatures of starting materials and helped to choose processing temperatures. XRD analysis was used to determine phase evolution. Solid state reaction sample contained a small amount of Sr3V2O8 as soon as after the first calcinations, but 100% of Sr3V2O8 did not appear until whole procedure was finished. Colloidal route turned out as an inconvenient method for preparation of pure phase. The final colloidal route sample contained 80% of Sr3V2O8, residual volume corresponded to Sr10V6O25. The most progressive phase evolution was detected in the sol-gel route. Raman an FTIR spectroscopy detected evolution of the first amount of Sr3V2O8 after gel heating at 250°C for 2 hours. The pure strontium vanadate was prepared after heating at 800°C for 2 hours.