Feifei Guo

Semiconductor/relaxor 0–3 type composites without thermal depolarization in Bi0.5Na0.5TiO3-based lead-free piezoceramics

Commercial lead-based piezoelectric materials raised worldwide environmental concerns in the past decade. Bi₀.₅Na₀.₅TiO₃-based solid solution is among the most promising lead-free piezoelectric candidates; however, depolarization of these solid solutions is a longstanding obstacle for their practical applications. Here we use a strategy to defer the thermal depolarization, even render depolarization-free Bi₀.₅Na₀.₅TiO₃-based 0-3-type composites. This is achieved by introducing semiconducting ZnO particles into the relaxor ferroelectric 0.94Bi₀.₅Na₀.₅TiO₃-0.06BaTiO₃ matrix. The depolarization temperature increases with increasing ZnO concentration until depolarization disappears at 30 mol% ZnO. The semiconducting nature of ZnO provides charges to partially compensate the ferroelectric depolarization field. These results not only pave the way for applications of Bi₀.₅Na₀.₅TiO₃-based piezoceramics, but also have great impact on the understanding of the mechanism of depolarization so as to provide a new design to optimize the performance of lead-free piezoelectrics.

Enhanced pyroelectric property in (1−x)(Bi0.5Na0.5)TiO3-xBa(Zr0.055Ti0.945)O3: Role of morphotropic phase boundary and ferroelectric-antiferroelectric phase transition

(1−x)(Bi0.5Na0.5)TiO3-xBa(Zr0.055Ti0.945)O3 (0 ≤ x ≤ 0.12) lead-free ceramics have been prepared and the morphotropic phase boundary (MPB) is confirmed to be x = 0.06–0.09. The MPB composition x = 0.07 shows enhanced pyroelectric properties from room temperature (RT) to the depolarization temperature Td (87 °C), with the pyroelectric coefficient p = 0.057 μC/cm2 °C and the figures of merit Fi = 203 pm/V, Fv = 0.022 m2/C, and Fd = 10.5 μPa−1/2 at RT and the highest pyroelectric coefficient of 2.21 μC/cm2 °C near Td. These values are superior to other lead-based/lead-free pyroelectric ceramics. Enhanced pyroelectric properties can be explained by the effects of MPB and ferroelectric-antiferroelectric phase transition.

Morphotropic phase boundary and electric properties in (1−x)Bi0.5Na0.5TiO3-xBiCoO3 lead-free piezoelectric ceramics

Lead-free (1−x)Bi0.5Na0.5TiO3-xBiCoO3 (x = 0, 0.015, 0.025, 0.03, 0.035, 0.04, and 0.06) piezoelectric ceramics have been synthesized and their structure and electric properties have been investigated systemically. The rhombohedral-tetragonal morphotropic phase boundary (MPB) locates near x = 0.025–0.035. For the ceramics with x = 0.025, the saturated polarization (Ps), remnant polarization (Pr), coercive field (Ec), strain(S), piezoelectric constant (d33), and thickness electromechanical coupling factor (kt) are 40.6 μC/cm2, 35.4 μC/cm2, 5.25 kV/mm, 0.11%, 107pC/N, and 0.45, respectively. The low temperature humps of relative dielectric constant, which is indicative of TR-T, are becoming inconspicuous gradually with the increasing x and almost disappear at x = 0.04. The depolarization temperature Td decreases first and then increases with the increasing x. Our results may be helpful for further work on Bi0.5Na0.5TiO3-based lead-free piezoelectric ceramics.

Refined crystal structures and phase transitions in 0.24Pb(In1/2Nb1/2)O3–0.43Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystal

Local lattice structures of 0.24Pb(In1/2Nb1/2)O3–0.43Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (0.24PIN–0.43PMN–0.33PT) single crystal have been investigated by Micro-Raman spectroscopy. A total of 12 Raman active modes were ascertained using the Gauss–Lorentzian line shape approximation, which confirmed that the 0.43PIN–0.26PMN–0.33PT single crystal has monoclinic symmetry at room temperature. The phase transitions were investigated by analyzing the temperature-dependent relative dielectric permittivity of both poled and unpoled 0.43PIN–0.26PMN–0.33PT single crystals measured upon heating. The monoclinic–tetragonal phase transition occurs at TM–T = 82 °C, and the Curie temperature is 199 °C. The splitting of (200) and (002) peaks in detailed X-ray diffraction spectra in the 2θ range of 44.6–45.2° during heating from room temperature to 200 °C was also studied. For a sample being poled along [111]c pseudo-cubic direction, several sharp peaks arise in the thermally stimulated depolarization current from 67 to 82 °C with the main peak occurs at 67 °C, which indicates that the depolarization temperature is 15 °C lower than the monoclinic to tetragonal phase transition and there are coexistence of monoclinic and rhombohedral phases in the [111]c poled single crystal.

Enhanced Electrical Properties of Novel Pb(Ni1/3Nb2/3)O3?BiScO3?PbTiO3 Ternary System near Morphotropic Phase Boundary

A novel xPb(Ni1/3Nb2/3)O3–(1-x)(0.30BiScO3–0.70PbTiO3) (PNN–BS–PT) ternary system was prepared by the columbite precursor method. The phase structure, microstructure, and electrical properties of ceramics of this system were investigated to identify the morphotropic phase boundary (MPB) composition of this system. The MPB with coexisting rhombohedral–tetragonal phases of PNN–BS–PT was located at approximately x=0.35, confirmed by their respective electric properties. With increasing PNN content, the coercive field EC, the Curie temperature TC, and the rhombohedral-to-tetragonal phase transition temperature TR–T were found to decrease and showed nearly linear dependences on their compositions. The enhanced properties were achieved in the MPB composition with x=0.35, which are as follows: dielectric constant er=3160 (1 kHz), piezoelectric coefficient d33=490 pC/N, and electromechanical coupling factor kp=0.44. In addition, a large bipolar strain on the order of 0.6% was achieved for the composition when an electrical field E=40 kV/cm was applied.