Abstract
Ceramics based on (Na1/2B1/2)TiO3 are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition. For example, the (1−x)(Na1/2Bi1/2)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 (Na1/2B1/2)TiO3-SrTiO3 and (Na1/2B1/2)TiO3-CaTiO3 were grown by the solid state crystal growth technique. Growth in the (Na1/2B1/2)TiO3-SrTiO3 system was sluggish whereas the (Na1/2B1/2)TiO3-CaTiO3 single crystals grew well. In the present work, 0.8(Na1/2Bi1/2)TiO3-0.2(Sr1−xCax)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 Ts and temperature of maximum relative permittivity Tmax, causing a decrease in inverse piezoelectric properties and a change from normal to incipient ferroelectric behavior.
Highlights
Restrictions introduced by the European Union and several countries on the use of lead in electronicJ Adv Ceram 2021, 10(5): 973–990 was discovered at x = 0.2–0.3 [4,5]
Matrix grain growth behaviour is an important factor in solid state crystal growth, as the driving force for single crystal growth is inversely proportionate to the mean matrix grain size [9]
Numerous works have noted the effect of composition change, dopant, or sintering aid addition on grain growth behaviour in NBT-based ceramics [10,11,12], but less work has been done on the effect of composition on solid state single crystal growth behaviour [13,14,15]
Summary
At compositions near the MPB, the electrical properties of the materials were significantly improved, and a shifting of the depolarization temperature Td as well as the rhombohedral–tetragonal phase transition temperature TR-T to lower temperatures was recognized This creates a limitation in the temperature operating range of NBT–ST materials, much affecting their practical application [6]. It may be possible to grow larger single crystals of 0.8(Na1/2Bi1/2)TiO3–0.2SrTiO3 by repressing matrix grain growth as well as altering the electrical properties of the single crystal. In the present work Ca is substituted for Sr in 0.8(Na1/2Bi1/2)TiO3–0.2SrTiO3 in order to study the effects on single crystal growth behaviour and electrical properties
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