Baihui Liu

Influence of structural evolution on energy storage properties in Bi0.5Na0.5TiO3-SrTiO3-NaNbO3 lead-free ferroelectric ceramics

Lead-free (1−x)(0.8Bi0.5Na0.5TiO3-0.2SrTiO3)-xNaNbO3 (x = 0–0.1, abbreviated as BNT-ST-xNN) ceramics were fabricated by a conventional sintering route with pure perovskite phase via XRD analysis. Raman spectrum was exploited in order to give an insight into the variation of local structural evolution. All compositions exhibited an obvious evolution of dielectric relaxation behaviors. Dielectric and ferroelectric properties clarified that a crossover from nonergodic to ergodic relaxor properties was obtained with the addition of NN content. A relatively large energy storage density was obtained WRec ∼ 0.74 J/cm3 at 7 kV/mm for x = 0.05 at room temperature. Particularly, the energy storage properties exhibited temperature (25–160 °C) and frequency stability (0.1–20 Hz) with WRec around 0.6 J/cm3 at 6 kV/mm for x = 0.05 within the ergodic region. Pulsed discharging current waveforms were measured under different electric fields to detect the energy storage density and discharging speed behavior. An illustrat...

Improving piezoelectric properties by controlling phase structure and crystal orientation

In this study, 〈001〉-textured (1 − x)K0.48Na0.52Nb0.96Sb0.04O3-xBi0.50(K0.48Na0.52)0.50Zr0.50Hf0.50O3 [abbreviated as (1 − x)KNNS-xBKNZH, x = 0.01–0.04] lead-free ceramics were prepared by templated grain growth (TGG) method and sintered by a two-step process. Excellent longitudinal piezoelectric coefficient d33 (434 pC N−1) and piezoelectric strain coefficient (722.5 pm V−1) are achieved in the textured 0.97KNNS-0.03BKNZH ceramics. The excellent piezoelectric properties can be ascribed to both the coexisting R–O–T multiphases and the 〈001〉 crystal orientation. In addition, a high electromechanical coupling coefficient kp (∼73.6%) is attained in textured ceramics with x = 0.02. The values of d33 and kp also display high thermal stability (with rate of change < ±10%) over 25–120 °C in textured ceramics with x = 0.03 and 0.04. Excellent comprehensive properties suggest that 〈001〉-textured (1 − x)KNNS-xBKNZH ceramics are promising lead-free candidates for actuator and transducer applications.

Tolerance factor effect on the structure and properties of KNN based ceramics at orthorhombic–tetragonal phase boundary

Abstract(1−x)(K0.5Na0.5)0.95Li0.05Nb0.93Sb0.07O3−xMZrO3 (M = Ca, Sr, Pb, Ba) ceramics with ABO3 structure were synthesized by conventional solid state reaction route. The effect of different kinds of dopant on orthorhombic–tetragonal (O–T) phase boundary and phase transition temperature were investigated, and the tolerance factor (t) of four kinds of zirconate dopants effect on piezoelectric properties was evaluated at O–T phase boundary. A quantitative relationship between O–T phase boundary and t was developed, the excellent piezoelectric properties was obtained when the t value at the O–T phase boundary in KNN-based lead free ceramics was around 0.9965–0.9990.