The evolution mechanism of defect dipoles and high strain in MnO2-doped KNN lead-free ceramics

Abstract

Defect dipoles in acceptor-doped (K0.5Na0.5)NbO3-based ceramics have a significant influence on their electrical properties. The present study examined the influence of the sintering atmosphere on the electrical properties of MnO2-doped (K0.5Na0.5)NbO3. The poled and aged samples sintered in the Ar atmosphere depicted unusual behavior related to the formation of defect dipoles (Mn2+Nb‴−VO··)′, aligned in the poling direction having larger polarity. The S-E loop of the poled and aged MnO2-doped (K0.5Na0.5)NbO3 ceramics sintered in the Ar atmosphere revealed larger strains in the poling direction and restrained strains in the opposite direction. Furthermore, it is observed that the unipolar electro-strain could reach 0.28% (d33* = 800 pm/V) at 3.5 kV/mm, a value nearly 5.6-fold higher than those obtained in the air atmosphere (0.05%). This method based on the sintering atmosphere and process control provides a promising way to obtain substantial electro-strain values suitable for applications in high-displacement actuators.

Giant electro‐strain in textured Li+‐doped 0.852BNT–0.11BKT–0.038BT ternary lead‐free piezoelectric ceramics

“…In addition, it is worth noting that the bipolar S‐E curves for both samples are asymmetrical (Figure A,B), indicating that there are some defects existed in these ceramics due to the volatility of A‐site alkali metal ions during high temperature sintering process. Compared with the random ceramics, the S‐E curves of the textured samples show greater asymmetry, which is attributed to more defect dipoles formed by A‐site vacancy and oxygen vacancy after aging with longer sintering time . Similar results have also been observed in {[Bi 0.5 (Na 0.84 K 0.16 ) 0.5 ] 0.96 Sr 0.04 }(Ti 0.075 Nb 0.025 )O 3 ceramics system .…”

Temperature stability and electrical properties of MnO‐doped KNN‐based ceramics sintered in reducing atmosphere

“…Its decreases first at 25‐100°C, then increase at 100‐190°C, finally decrease sharply again. The spontaneous polarization P s could be switched toward the direction of the applied electric field to generate an electro‐strain due to the switch and extension of P s . However, there is an interaction between defect dipoles and spontaneous polarization P s inside domains .…”

“…The spontaneous polarization P s could be switched toward the direction of the applied electric field to generate an electrostrain due to the switch and extension of P s . 50,51 However, there is an interaction between defect dipoles and spontaneous polarization P s inside domains. 46 The defect dipole ðMn 00 Zr À V :: o Þ in the poled (35 kV/cm)/aged (3 days) Mn 0.8 ceramics must be negative to the extension of P s .…”

Effect of MnO2on the dielectric properties of Nb‐doped BaTiO3‐(Bi0.5Na0.5)TiO3ceramics for X9RMLCCapplications

“…The IR of the 0.2 mol% Mn‐doped ceramic is 24.9 × 10 12 Ω/cm, which is the highest among all of the Mn‐doped ceramics. It has been reported that MnO 2 can convert to diverse valence states when heated: …”