Well-defined double hysteresis loop in NaNbO3 antiferroelectrics.

Antiferroelectrics (AFEs) are promising candidates in energy-storage capacitors, electrocaloric solid-cooling, and displacement transducers. As an actively studied lead-free antiferroelectric (AFE) material, NaNbO3 has long suffered from its ferroelectric (FE)-like polarization-electric field (P-E) hysteresis loops with high remnant polarization and large hysteresis. Guided by theoretical calculations, a new strategy of reducing the oxygen octahedral tilting angle is proposed to stabilize the AFE P phase (Space group Pbma) of NaNbO3. To validate this, we judiciously introduced CaHfO3 with a low Goldschmidt tolerance factor and AgNbO3 with a low electronegativity difference into NaNbO3, the decreased cation displacements and [BO6] octahedral tilting angles were confirmed by Synchrotron X-ray powder diffraction and aberration-corrected scanning transmission electron microscopy. Of particular importance is that the 0.75NaNbO3-0.20AgNbO3-0.05CaHfO3 ceramic exhibits highly reversible phase transition between the AFE and FE states, showing well-defined double P-E loops and sprout-shaped strain-electric field curves with reduced hysteresis, low remnant polarization, high AFE-FE phase transition field, and zero negative strain. Our work provides a new strategy for designing NaNbO3-based AFE material with well-defined double P-E loops, which can also be extended to discover a variety of new lead-free AFEs.

Correction: Improving the piezoelectric strain and anti-reduction properties of K0.5Na0.5NbO3-based ceramics sintered in a reducing atmosphere.

Correction for 'Improving the piezoelectric strain and anti-reduction properties of K0.5Na0.5NbO3-based ceramics sintered in a reducing atmosphere' by Zhenyong Cen et al., Dalton Trans., 2021, 50, 8851-8862, DOI: 10.1039/D1DT01059J.

Improving the piezoelectric strain and anti-reduction properties of K0.5Na0.5NbO3-based ceramics sintered in a reducing atmosphere.

Lead-free 0.945K0.48Na0.52Nb0.96Ta0.04O3-0.055BaZrO3 + 6%MnO + xZrO2 piezoelectric ceramics sintered in a reducing atmosphere were prepared by conventional solid-state reaction methods. The use of the ZrO2 dopant resulted in an increase in the rhombohedral (R) phase in orthorhombic (O)/R coexisting phases. Nonstoichiometric ZrO2 dopant addition could effectively improve the anti-reduction properties of KNN-based ceramics via controlling the oxygen vacancy concentration. In particular, 2% mol nonstoichometric ZrO2 dopant addition could improve the activation energy of the grain boundary (Egb) via increasing the grain boundary thickness. The addition of the ZrO2 dopant could improve the fatigue resistance of the unipolar piezoelectric strain of 0.945K0.48Na0.52Nb0.96Ta0.04O3-0.055BaZrO3 + 6%MnO ceramics. The optimum inverse piezoelectric coefficient of ceramics at x = 0.01 reached up to ∼465 pm V-1 at a low driving electric field E of 20 kV cm-1 at room temperature, and the temperature stability of reached 155 °C. After 106 unipolar fatigue cycles, the ß value of 0.945KNNT-0.055BZ + 6Mn + xZr ceramics could be preserved to more than 86%. The 0.945K0.48Na0.52Nb0.96Ta0.04O3-0.055BaZrO3 + 6%MnO + xZrO2 ceramic is a lead-free material with great potential to be applied in the fabrication of multilayer ceramic actuators with Ni inner electrodes in the future.

Significantly improved piezoelectric performance of PZT-PMnN ceramics prepared by spark plasma sintering.

A high-performance piezoelectric material, 0.95Pb(Zr0.52Ti0.48)O3-0.05Pb(Mn1/3Nb2/3)O3 (PZT-PMnN) ceramic, was prepared by using a spark plasma sintering (SPS) method. By systematically comparing the electrical properties, the spark-plasma-sintered sample was demonstrated to be superior to a conventionally sintered sample. With respect to conventionally sintered ceramic, the d 33 of spark-plasma-sintered ceramic increases from 323 pC/N to 412 pC/N, and the increases from 318 pm V-1 to 553 pm V-1. More importantly, the mechanical quality factor (Q m) reaches 583, which is three times higher than the conventionally sintered sample (Q m ∼ 182). Furthermore, the SPS method was found to be capable of promoting other electrical properties simultaneously. Therefore, the SPS method is proposed to be an effective processing method to fabricate PZT-PMnN ceramics of higher performance.

Temperature independence of piezoelectric properties for high-performance BiFeO3-BaTiO3 lead-free piezoelectric ceramics up to 300 °C.

The temperature-dependence behaviors of ferroelectric, piezoelectric, k p and electrical-field-induced strain were carefully evaluated for high-performance BiFeO3-0.3BaTiO3 (BF-0.3BT) ceramics. There results indicate, combined with Rayleigh analysis and temperature-dependence XRD and PFM, that the increase of strain and large signal with increasing the temperature from room temperature to 180 °C is related to the joint effect of intrinsic contribution (lattice expansion) and extrinsic contribution (domain switching). With further increasing the temperature to 300 °C, the large signal d 33 and electrical-field-induced strain mildly decrease because of the increase of conductivity for BF-0.3BT ceramics. However, different from strain and large signal the small signal d 33(E0) and k p exhibit excellent temperature stability behavior as the temperature increases from room temperature to 300 °C.