The Preparation of (Tl1Pb1-xMx)Sr2Ca2Cu3O9-δ Superconductor via Stoichiometric Reaction

The (Tl 1 Pb 1-x M x )Sr 2 Ca 2 Cu 3 O 9-δ superconductor with M=Bi and Cr has been prepared by solid state reaction method. The preparation of the precursor material using metal oxides powder of  high purity(>99.99%) Strontium Oxide, Calcium Oxide and Copper Oxides. The powder were mixed completely and heated at 900 o C for 48 hours with several intermediate grindings. An appropriate amounts of Tl 2 O 3 and Cr 2 O 3 /Bi 2 O 3 (mole%) were then added to the precursor and completely mixed before being pressed into pellets form of 1.3 cm in diameter and 0.2 cm in thickness under 7 ton/cm 2 of pressure and then first heated at 900°C in the flowing oxygen for 4 minutes, followed by furnace cooling to room temperature. The dc electrical resistance measurement in a range of 300K-50K were carried out using the four-point method with silver paste contact in conjunction with a closed cycle refrigerator from CTI Cryogenic Cycle Refrigerator Model 22. We observed that T c zero was changed from 69K to 70K and T c onset from 88K to 90K with addition of 0.1mole-% Cr 2 O 3 . When 0.2 mole-% Cr 2 O 3 was introduced, the T c zero decresed to 65K. It has been noted the addition of Bi 2 O 3 could not enhanced the T c zero as well as T c onset . All samples showed metallic characteristic at normal state.