Effects of A-Site Ions on the Phase Transition Temperatures and Dielectric Properties of (1-x)(Na0.5K0.5)NbO3–xAZrO3 Solid Solutions

(1-x)(Na0.5K0.5)NbO3–xAZrO3 (A = Sr, Ca) solid solutions have been prepared to study the effcts of A-site ions on the successive phase transition temperatures. It is found that the phase diagram for the solid solutions are very similar: with increasing x, the cubic–tetragonal phase transition temperature TC–T and the tetragonal–orthorhombic phase transition temperature TT–O shift to the lower-temperature region, while the orthorombic–rhombohedral phase transition temperature TO–R shifts to the higher temperature region. When x is between 8 and ~15 molar percentage, the orthorhombic–rhombohedral phase transition temperature is higher than room temperature and the (1-x)(Na0.5K0.5)NbO3–xAZrO3 solid solutions exhibit rhombohedral symmetry at room temperature. It is found that TC–T is affected by A-site ions; while TT–O and TO–R are almost independent of A-site ions.