PHASE-FORMATION AND THERMAL-STABILITY OF THE COMPOUNDS IN THE BI2O3-PBO SYSTEM

The scientific interest for the Bi2O3-PbO system has increased due to the importance of the PbO in the high-T-c superconducting phase format ion in the Bi2O3-SrO-CaO-CuO system. Also Bi2O3-PbO system contains co mpounds with some specific semiconductor and dielectric properties and Bi2O3-based solid solutions are well known as high oxygen ion conduct ors. Previously, several low melting defined compounds have been ident ified in the system: 6Bi(2)O(3).PbO; 3Bi(2)O(3).2PbO; 4Bi(2)O(3).5PbO; 4Bi(2)O(3).6PbO and Bi2O3.3PbO. This work deals with the phase format ion and thermal stability of these compounds. Under non-isothermal con ditions, in all mixtures regardless of the Bi2O3/PbO ratio, the compou nd 6Bi(2)O(3).PbO is preferentially formed, followed by the compound 4 Bi(2)O(3).5PbO. The formation of the compound 4Bi(2)O(3).6PbO was not confirmed while the formation of the compound Bi2O3. 3PbO occurs throu gh a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isoth ermal conditions in the same temperature range the tendency to form th e stoichiometric compounds increases. All compounds form, decompose an d melt at temperatures between 530-780 degrees C.