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 formation in the Bi2O3-SrO-CaO-CuO system. Also Bi2O3-PbO system contains compounds with some specific semiconductor and dielectric properties and Bi2O3-based solid solutions are well known as high oxygen ion conductors. Previously, several low melting defined compounds have been identified 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 formation and thermal stability of these compounds. Under non-isothermal conditions, in all mixtures regardless of the Bi2O3/PbO ratio, the compound 6Bi(2)O(3).PbO is preferentially formed, followed by the compound 4Bi(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 through a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isothermal conditions in the same temperature range the tendency to form the stoichiometric compounds increases. All compounds form, decompose and melt at temperatures between 530-780 degrees C.