Morphotropic Phase Boundary and Electrical Properties of Bisumuth Sodium Titanate–Potassium Niobate Solid-Solution Ceramics

A morphotropic phase boundary (MPB) between (Bi 1/2 Na 1/2 )TiO 3 (rhombohedral system) and KNbO 3 (orthorhombic system) was determined by using X-ray diffraction and dielectric measurements. A solid solution, (1- x )(Bi 1/2 Na 1/2 )TiO 3 – x KNbO 3 [BNTK-100 x ], shows a rhombohedral symmetry and orthorhombic symmetry at a composition of around 0≦ x ≦0.95 and 0.96≦ x ≦1.00, respectively. The dielectric constant, ε s , at Curie temperature, T c , was the largest value in the BNTK-96 system. From these results, the MPB of the BNTK system seems to exist in BNTK-96. The BNTK ceramics were confirmed to be ferroelectric by observing their hysteresis loops. Resistivities, ρ, of BNTK-100 x (0.94≦ x ≦0.98) are 10 9 –10 12 Ω·cm. An electromechanical coupling factor, k 33 , of BNTK-96 is 0.16 which is an unsaturated value.