Crystal structure, dielectric properties of (K_0.5Na_0.5)NbO₃ single crystal grown by flux method using B₂O₃ flux

Abstract

Lead free piezoelectric single crystals of sodium potassium niobate (K 0.5 Na 0.5 )NbO 3 (KNN) were grown by high-temperature solution method using two different fluxes; one with a mixture of NaF and KF and other with addition of B 2 O 3 along with the mixture. In the present study, the growth of KNN crystals without B 2 O 3 flux and the same with B 2 O 3 flux were compared. It was found that additions of small amounts of B 2 O 3 lowered the melting temperature of the solid solution and enabled better dielectric properties. Phase analysis showed that all samples were crystallized in pure orthorhombic perovskite phase. AFM morphological studies showed that the addition of B 2 O 3 flux increased the roughness of the grown crystal. Further, addition of B 2 O 3 flux slightly decreased the orthorhombic to tetragonal phase transition temperature T (O-T) and the Curie temperature T C . The ferroelectric behaviour of KNN single crystal has been investigated at room temperature. The crystal grown using B 2 O 3 flux exhibited a remanent polarization (P r ) ∼ 32 μC/cm 2 and coercive field (Ec) of ∼11.8 kV/cm whereas the crystal grown without the use of B 2 O 3 flux had a remanent polarization (P r ) ∼ 36 μC/cm 2 and coercive field (Ec) of ∼14.6 kV/cm.

Dielectric, piezoelectric, and elastic properties of K0.8Na0.2NbO3 single crystals

“…[5][6][7] A significant breakthrough towards improving the dielectric and piezoelectric properties of KNN was made by Saito et al in 2004, by changing the temperatures of the morphotropic phase boundaries (MPBs) and the Curie temperatures at which the piezoelectric coefficients of KNN-based ceramics reach 416 pC N -1 . [14][15][16][17][18] However, as a result of restrictions due to the size and quality of pure KNN single crystals, only a small number of material properties have been reported in the literature. [9][10][11][12] Nevertheless, it is difficult to directly study the internal properties of a KNN material compared with single crystals, because of the gain boundaries in these ceramics.…”

“…8 Since then, a number of intensive studies have been conducted to improve both the preparation techniques and the piezoelectric properties of KNN. To date, only the piezoelectric strain constant d 33 and the electromechanical coupling factor k t have been measured in the majority of reports, 13,14,19 and no other single complete set of material constants for pure KNN single crystals has been reported. 13 In addition, single crystals can be poled along different crystallographic directions in order to study their piezoelectric properties; this means that we would require large-sized pure KNN single crystals in order to conduct fundamental investigations.…”

“…The most widely used techniques are the flux and Bridgman methods. [14][15][16][17][18] However, as a result of restrictions due to the size and quality of pure KNN single crystals, only a small number of material properties have been reported in the literature. To date, only the piezoelectric strain constant d 33 and the electromechanical coupling factor k t have been measured in the majority of reports, 13,14,19 and no other single complete set of material constants for pure KNN single crystals has been reported.…”

Orientation dependence of electrical properties of large-sized sodium potassium niobate lead-free single crystals

“…The KNN crystals grown by a flux method, using fluxes such as NaF, a KF-NaF mixture and NaBO 2 , [13][14][15][16][17] display enhanced quality, yet the size of the crystals is relatively small. Relatively large-sized KNN crystals were obtained by Saravanan et al 18 by adding boron trioxide (B 2 O 3 ) into the mixture of KF and NaF fluxes; the dielectric and piezoelectric properties were enhanced this way. The Bridgeman method has also been employed by Chen et al 19 to grow large-sized Li-doped KNN crystals with a piezoelectric coefficient of up to 405 pC N −1 ; nevertheless, the relatively high leakage current leads to unsaturated polarization hysteresis loops.…”

Temperature‐ and E‐field‐dependent domain configuration and electrical properties in (K, Na, Li)(Nb, Ta, Sb)O3 single crystal

“…The intrinsic response can also be easily obtained due to the anisotropic lattice structure in single crystals. Therefore, we choose single crystal to carry out our study in this work …”