| dc.description.abstract | Two series of the Tl-based (T1-2212) high temperature superconductor, Th2-xCryBa2CaCu2O8- and Th2-TexBa2 CaCu2O-s have been prepared via solid state reaction. The substitution of Cr and Te to the TI-site is aimed to investigate the role of Cr and Te on the superconductivity, critical transition temperature, phase stability as well as resistivity at normal state of T1-2212 superconductor. The samples were prepared by solid state reaction method and had been accomplished in two stages: the first, Ba2CaCu2O precursor material was synthesized using BaCO3(99.9%, Aldrich), CaO(99.99%, Alfa Aesar) and CuO(99.9%, Alfa Aesar) as starting compound. These compounds were mixed in an appropriate ratio before sintering at 900°C for 24h followed by cooling to room temperature at standard pressure. The precursor was then ground for about 1h and mixed with Th2O3 (99.9%, Alfa Aesar) and Cr2O3(99.9%, Merck)/Te2O3(99.9%, Alfa Aesar) to produce Th2-CryBa2CaCu2O/T2-Te,Ba2CaCu2Os. The pellet was produced with a SPECAC hydraulic compressor with a pressure of 7 tons for 10 minutes. The pellets were heated at 900°C in a tube furnace with oxygen flow for 4 minutes. Four-point probe method was applied to the Te measurement. The current source Keithley 220 Programmable Current Source and a Keithley 2000 Autoranging Microvolt DMM was used. In cooling procedure, a vacuum pump of model Edwards Cryogenics 8200 Compressor and CTL- Cryogenesis Model 22 refrigerator were used and the temperature was controlled by a controller model Lakeshore 325 autotuning temperature controller. Critical temperature, T. was determined using the standard four point probe technique fitted with a closed-cycle Helium cooling system and the system measures the voltage from 50 K to 300 K in a fixed current of 20 mA. Van der Pauw method was applied to determine the resistivity at normal state. It was found that a maximum critical temperature with Tc zero: 96 K and Tc onset 116 K has been achieved in the composition of Th1.8Cг02Ba2CaCu2O8-8. The TI-2212 phase in this composition was 88% with c-lattice parameter= 29.388A°. Most of the samples were in 14/mmm space group. The enhancement of Tc zero up to 100 K and Tc onset 115 K was observed in the composition of Th19Te01Ba2 CaCu2O8-8 (BaO precursor). The T1-2212 phase occurrence in this composition was 92% with c-lattice parameter 29.2596A°. The composition of Th16Teo4Ba2 CaCu2O8-5 (BaCO3) precursor has a Te zero: 98 K and Te onset :111 K. The TI-2212 phase was 84% and c-lattice parameter=29.2100A°. The results showed that the phase occurrence affected the critical temperature. The value of coherent length, c(0) tent to increase with increasing of Cr and Te content. All of the samples showed a single peak at Tcp | en_US |
