Phase diagram of the Bi₄Ti₃O₁₂-BaTiO ₃-(Na_1/2Bi_1/2)TiO₃ system

The phases formed in the ternary system (Na12Bi12)TiO3-Bi4Ti3O12-BaTiO3 (NBT-BTO-BT) were studied at 1150°C in air. A very accurate picture of the ternary phase diagram was obtained examining almost 90 different compositions, exploiting low-angle XRD analyses to study the layer compounds. New compounds with five perovskite blocks (m=5) were discovered deep in the phase diagram. No compounds with m>5 were found. It was also established that pure perovskite compounds can be obtained only at compositions very close to the NBT-BT line. The relationships between the phases is discussed and it is hypothesized that the number of perovskite blocks in the system is determined by charged sites being created by the progressive substitution of Bi3+ in the A site of the perovskite blocks of BTO with the A cations of the perovskite end-member.