Low‐Temperature Synthesis of Lead Tantalate Pyrochlore Solid Solutions Pb _{1.5+ x} (Ta _{2− y} Pb _y )O _7−δ (0.0 < x < 0.5; 0.0 < y < 0.6)

Synthesis of lead tantalate pyrochlores by the reaction of PbO and Ta ₂ O ₅ in various molar ratios between 1.5 and 4.0 at low temperatures (500–650°C) has been carried out. It has been shown that when PbO is reacted with Ta ₂ O ₅ in various molar ratios at low temperatures, metastable lead tantalate pyrochlore solid solutions having cubic symmetry are formed. X‐ray diffraction data give evidence for an increase in the a lattice parameter with increasing PbO content and partial occupancy of Pb in the Ta sites leading to the formula Pb _{1.5+ x} ²⁺ (Ta _{2− y} Pb _y ⁴⁺ )O _7−δ (0.0 < x < 0.5; 0.0 < y < 0.6) for this phase. It has also been found that the intermediate members of the solid solutions are metastable and tend to segregate into Pb‐deficient and Pb‐excess compositions leading to significant compositional inhomogeneity for the intermediate members.