Abstract
(1-x)K0.4Na0.6NbO3–xBiFeO3 lead-free piezoelectric ceramics were successfully prepared in a single perovskite phase using the conventional solid-state synthesis. Relative permittivity (er) as a function of temperature indicated that small additions of BiFeO3 not only broadened and lowered the cubic to tetragonal phase transition (TC) but also shifted the tetragonal to orthorhombic phase transition (TO–T) toward room temperature (RT). Ceramics with x = 1 mol.% showed optimum properties with small and large signal piezoelectric coefficient, d33 = 182 pC/N and d∗33 = 250 pm/V, respectively, electromechanical coupling coefficient, kp = 50%, and TC = 355°C. kp varied by ∼5% from RT to 90°C, while d∗33 showed a variation of ∼15% from RT to 75°C, indicating that piezoelectric properties were stable with temperature in the orthorhombic phase field. However, above the onset of TO–T, the properties monotonically degraded in the tetragonal phase field as TC was approached.
Highlights
Piezoelectric materials are essential in many applications and used in different electronic circuits as a sensor, actuator, or a transducer (Holterman and Groen, 2013)
In our samples at x = 0, obvious split of the 200 peak was detected at 2θ ∼ 46◦ which is consistent with the orthorhombic phase frequently reported for K0.5Na0.5NbO3 ceramics
An investigation of the (1-x)K0.4Na0.6NbO3–xBiFeO3 system revealed that dense ceramics can be obtained for x ≤ 1 mol.%
Summary
Piezoelectric materials are essential in many applications and used in different electronic circuits as a sensor, actuator, or a transducer (Holterman and Groen, 2013). Amongst the potentially useful lead-free piezoelectrics, only Ca2+ and Zr4+ modified BaTiO3 and (Na,K)NbO3-based ceramics have low coercive fields similar to lead zirconate titanate (PZT). New phase boundaries have been constructed in (K,Na)NbO3 based ceramics by simultaneously moving the rhombohedral and tetragonal phases toward RT Such a coexistence of rhombohedral-orthorhombictetragonal phase boundaries has been very successful in improving the d33 values and have significantly improved the temperature stability in these ceramics (Tao et al, 2019; Lv et al, 2020; Zheng et al, 2020). BiFeO3 is one of the most extensively investigated perovskite compounds because of its RT multiferroic properties (Khesro et al, 2016a) It is rarely, (Sun et al, 2008; Zuo et al, 2008) investigated in solid solution with (K,Na)NbO3. The planar electromechanical coupling factor (kp) was determined from the resonance and antiresonance frequencies peaks, which were measured using an Agilent 4294A impedance/gainphase analyzer according to IEEE standards on piezoelectricity (American and Standard, 1988)
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