Growth of single crystals in the (Na_1/2Bi_1/2)TiO₃-(Sr_1-xCa_x)TiO₃ system by solid state crystal growth

Ceramics based on (Na_1/2B_1/2)TiO₃ are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition. For example, the (1-x)(Na_1/2Bi_1/2)TiO₃-xSrTiO₃ system exhibits a morphotropic phase boundary at x = 0.2-0.3, leading to high values of inverse piezoelectric constant d^*₃₃, which can be further improved by the use of single crystals. In our previous work, single crystals of (Na_1/2B_1/2)TiO₃-SrTiO₃ and (Na_1/2B_1/2)TiO₃- CaTiO₃ were grown by the solid state crystal growth technique. Growth in the (Na_1/2B_1/2)TiO₃-SrTiO₃ system was sluggish whereas the (Na_1/2B_1/2)TiO₃-CaTiO₃ single crystals grew well. In the present work, 0.8(Na_1/2Bi_1/2)TiO₃-0.2(Sr_1-xCa_x)TiO₃ single crystals (with x = 0.0, 0.1, 0.2, 0.3, 0.4) were produced by the solid state crystal growth technique in an attempt to improve crystal growth rate. The dependence of mean matrix grain size, single crystal growth distance, and electrical properties on the Ca concentration was investigated in detail. These investigations indicated that at x = 0.3 the matrix grain growth was suppressed and the driving force for single crystal growth was enhanced. Replacing Sr with Ca increased the shoulder temperature T_s and temperature of maximum relative permittivity T_max, causing a decrease in inverse piezoelectric properties and a change from normal to incipient ferroelectric behavior.