THERMODYNAMIC STABILITIES OF TERNARY OXIDES IN THE BA-PB-O SYSTEM BY THE EMF TECHNIQUE

The perovskite-type compound BaPbO3 in the Ba-Pb-O system is of consid erable interest in materials science and technology owing to its wide- ranging electronic and chemical applications. To determine the thermod ynamic stabilities of this compound and related plumbates, the e.m.f. of the galvanic cells using both oxide and fluoride solid electrolytes and with (a) BaPbO3-Ba4Pb3O10,-PbO, (b) Ba4Pb3O10,-Ba2PbO4-PbO and (c ) BaPbO3-Pb3O4-BaF2 as the test electrodes have been studied over the temperature ranges 756-968 K, 797-1097 K and 695-880 K respectively. T he least-squares analysis and further processing of the e.m.f data tog ether with the standard Gibbs energies Delta G(f) of formation of bina ry oxides from the literature have yielded the expressions (1) Delta G (f)(o)(BaPbO(3)s) +/- 1.00 (kJ mol(-1)) = -901.56 + 0.26596 T (K) (2) Delta G(f)(o)(Ba4Pb3O10,s) +/- 3.5 (kJ mol(-1)) = -3278.95 + 0.89356 T (K)and (3) Delta G(f)(o)(Ba2PbO4,s) +/- 2.08 (kJ mol(-1)) = -1482.10 + 0.37421 T (K) These data together with phase equilibrium studies hav e been made use of in constructing the Ba-Pb-O phase diagram at 800 K.