FORMATION AND TRANSFORMATION OF CUBIC 3PBO.2TA2O5 SOLID-SOLUTION

The formation of lead tantalates in the PbO-rich region is studied using the powders prepared by the simultaneous hydrolysis of lead and tantalum alkoxides. Cubic 3PbO . 2Ta2O5 solid solutions crystallize at low temperatures from amorphous materials between 60 and 75 mol% PbO. The lattice parameter, a, increases linearly from 1.0545 to 1.0705 nm with increasing PbO. At higher temperatures the solid solutions above 66.67 mol% PbO are transformed into those of rhombohedral 2PbO . Ta2O5. Rhombohedral 5PbO . 2Ta2O5 is formed at approximately 850 to 900-degrees-C by transformation of 2PbO . Ta2O5 solid solution corresponding to 71.43 mol% PbO. The existence of previously reported 3PbO . Ta2O5 is not confirmed.