Phase relations, dielectric and piezoelectric properties of ceramics in the system (Bi0.5Na0.5)TiO3-PbTiO3

A part of the phase diagram of the (Bi0.5Na0.5)1-x Pb x TiO3 system at the (Bi0.5Na0.5)TiO3 side was constructed on the basis of X-ray diffraction data, dielectric measurements and D-E hysteresis observations. A rhombohedral (Fα)-tetragonal (Fβ) morphotropic phase boundary (MPB) at room temperature is shown to exist at x = 0.13. An intermediate antiferroelectric phase has been observed in the composition range of 0 ⩽ x ⩽ 0.16 of this system. Near the MPB rhombohedral compositions (x ≒ 0.12) undergo a ferroelectric rhombohedral (Fα)-ferroelectric tetragonal (Fβ)-antiferroelectric(A)-paraelectric (P) sequence of transitions at elevated temperatures. It was found that the Mn-doped MPB material (x = 0.12) has a lower free permittivity ϵ T 33 (= 338), a higher longitudinal coupling factor k33 (= 53%), a higher mechanical quality factor QM (= 944) and favorable mechanical characteristics for piezoelectric ceramics in high power ultrasonic uses, or actuator applications. These low-lead-content ceramics have proved to have reproducible properties and are economic to fabricate.