Microstructure, Piezoelectric, and Ferroelectric Properties of Bi₂O₃‐Added (K_0.5Na_0.5)NbO₃ Lead‐Free Ceramics

Abstract

Lead‐free piezoelectric (K0.5Na0.5)NbO3–x wt% Bi2O3 ceramics have been synthesized by an ordinary sintering technique. The addition of Bi2O3 increases the melting point of the system and improves the sintering temperature of (K0.5Na0.5)NbO3 ceramics. All samples show a pure perovskite phase with a typical orthorhombic symmetry when the Bi2O3 content <0.7 wt%. The phase transition temperature of orthorhombic–tetragonal (TO−T) and tetragonal–cubic (TC) slightly decreased when a small amount of Bi2O3 was added. The remnant polarization Pr increased and the coercive field Ec decreased with increasing addition of Bi2O3. The piezoelectric properties of (K0.5Na0.5)NbO3 ceramics increased when a small amount of Bi2O3 was added. The optimum piezoelectric properties are d33=140 pC/N, kp=0.46, Qm=167, and TC=410°C for (K0.5Na0.5)NbO3–0.5 wt% Bi2O3 ceramics.

Ferroelectric domain structures in &lt;001&gt;-oriented K0.15Na0.85NbO3 lead-free single crystal

“…[2][3][4] A lot of investigations have been focusing on modifying the piezoelectric properties of KNN ceramics by doping metal ions, introducing perovskite oxides to form new solid solution and adopting different sintering methods such as hot pressing and spark plasma. 5 Besides KNN ceramics, the KNN-based single crystals have been grown to further improve the piezoelectric properties, because single crystals can be poled along different directions by domain engineering method. [6][7][8][9] The behavior of a ferroelectric is mainly dependent on the local domain response by applying an electrical loading.…”

Electrical properties of B site substituted (K0.48Na0.52)(W2/3Bi1/3)xNb1−xO3 piezoceramics

“…As can be seen, the sample of x = 0.008 exhibits the highest d 33 , k p values while maintaining the highest Q m and lowest tand. That is, 0.008 mol% (W 2/3 Bi 1/3 ) doping has induced ''hard'' and ''soft'' effects simultaneously and this may be related to the different valences of W and Bi since Bi 2 O 3 only plays a ''soft'' role for KNN ceramics [18]. Figure 3 shows the frequency dependence of phase angle between 250 and 300 kHz.…”

“…Therefore, the outstanding piezoelectric properties of (Li, Sb, Ta) modified KNN ceramics are not thermally stable owing to the narrow temperature region for the existence of PPB. In order to get improved and thermally stable piezoelectric properties, many researches have been done on the formation of solid solutions (e.g., KNN-BaTiO 3 , KNN-CaTiO 3 , KNN-BiFeO 3 ) [10][11][12][13][14][15][16][17] and ''soft''/ ''hard'' doping (e.g., MnO, CdO, Bi 2 O 3 ) [18][19][20][21]. Although some parameters such as the mechanical quality factor Q m , and the electromechanical coupling coefficient k p showed large enhancement, the important piezoelectric constant d 33 shows lower values than the results for (Li, Sb, Ta) substituted KNN ceramics.…”

Alkali Niobate Piezoelectric Ceramics

“…In order to improve their poor sinterability, special techniques such as a hot pressing have been employed. Recent study shows that by choosing appropriate additives as sintering aids, such as Bi 2 O 3 or CuO [122][123][124][125] or complex oxides such as K 4 CuNb 8 O 23 [91][92][93][94][95], well-sintered alkali niobate ceramics can be obtained. Compositional modifications to alkali niobate ceramics were also proven to be effective in order to obtain well-sintered materials.…”