Abstract
The structural, electromechanical, and dielectric properties of (1 − x)(0.8Na0.5Bi0.5TiO3-0.2BaTiO3)-xCaTiO3 [(1 − x) (0.8NBT-0.2BT)-xCT] ceramics are studied as candidates for room temperature actuators with high field-induced strain. The choice of 0.8NBT-0.2BT as a starting composition is motivated by the large tetragonality in this concentration range, even though it is located far away from the morphotropic phase boundary. CaTiO3 was chosen as a third component to decrease the depolarization temperature and achieve a high field-induced strain at room temperature. The measured strains at the field-induced phase transition are remarkably lower than might be expected from the jump in unit cell parameters at the phase transition. This inconsistency could be related to an incomplete field-induced phase transition from the ferroelectric phase to the nonpolar phase. Among all of the manufactured samples, the phase transition is close to room temperature in the composition with x = 0.100, which allows obtaining unipolar strains up to 0.23% at E = 65 kV/cm. Electrostrictive-like strain was observed not only above the depolarization temperature but also in the region of field-induced phase transition.
Highlights
Na0.5Bi0.5TiO3 (NBT) based compositions are widely studied due to environmental requirements, which necessitate the replacement of lead-containing ferroelectrics in a large variety of devices applying the piezoelectric effect
In lead-containing ferroelectric solid solutions, the highest piezoelectric coefficients are found in the region of the morphotropic phase boundary (MPB) between ferroelectric phases possessing different symmetries
In the NBT-based solid solutions, it is a boundary between the ferroelectric and nonpolar states, and the relationship with the rhombohedral–tetragonal phase boundary, observed in the unmodified compositions such as 0.94NBT-0.06BT and 0.84NBT-0.16KBT, is not quite clear, except for an indirect role—Td reaches a minimum at the MPB.5,6
Summary
Na0.5Bi0.5TiO3 (NBT) based compositions are widely studied due to environmental requirements, which necessitate the replacement of lead-containing ferroelectrics in a large variety of devices applying the piezoelectric effect. In lead-containing ferroelectric solid solutions, the highest piezoelectric coefficients are found in the region of the morphotropic phase boundary (MPB) between ferroelectric phases possessing different symmetries.4 Such an approach was applied in the case of solid NBT-based solutions, focusing on the rhombohedral–tetragonal MPB in Na0.5Bi0.5TiO3–BaTiO3 (NBT–BT) and Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 (NBT–KBT) solid solutions. In the temperature region of Td, double hysteresis loops are observed together with large field-induced strain, corresponding to the phase transition between the antiferroelectric and ferroelectric states.. In the NBT-based solid solutions, it is a boundary between the ferroelectric and nonpolar states, and the relationship with the rhombohedral–tetragonal phase boundary, observed in the unmodified compositions such as 0.94NBT-0.06BT and 0.84NBT-0.16KBT, is not quite clear, except for an indirect role—Td reaches a minimum at the MPB.5,6 Such MPB has a pronounced temperature dependence In the NBT-based solid solutions, it is a boundary between the ferroelectric and nonpolar states, and the relationship with the rhombohedral–tetragonal phase boundary, observed in the unmodified compositions such as 0.94NBT-0.06BT and 0.84NBT-0.16KBT, is not quite clear, except for an indirect role—Td reaches a minimum at the MPB. Second, such MPB has a pronounced temperature dependence
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