Li-Feng Zhu

High piezoelectricity of BaTiO3–CaTiO3–BaSnO3 lead-free ceramics

A series of solid solutions of BaTiO3–x(0.4CaTiO3–0.6BaSnO3) (abbreviated as BT–x(CT–BS), x = 0.00–0.20 mol) were prepared to search for high performance lead-free piezoelectric ceramics. Through content tailoring, a complex phase transition was confirmed by X-ray diffraction and Raman spectra as well as temperature dependence of the dielectric constant, which occurs from tetragonal(T)–orthorhombic(O) coexistence at 0 ≤ x ≤ 0.12 to rhombohedral(R)–O–T and R–O/T–cubic(C) multiphase coexistence at x = 0.16 and 0.20, respectively. The lower EC = 1.31 kV cm−1 and higher Pr = 9.48 μm cm−2 as well as high piezoelectric response d33 = 570 pC N−1 were achieved in BT–x(CT–BS) ceramics at an optimal composition of x = 0.16. The ultrahigh converse piezoelectric coefficient d*33 = 1444 pm V−1 and strain = 0.070% which are the highest values reported so far in lead-free ceramics also were achieved at x = 0.16, suggesting that a BT–x(CT–BS) system is a promising lead-free alternative material for electromechanical actuator applications.

Phase transition and high piezoelectricity in (Ba,Ca)(Ti1−xSnx)O3 lead-free ceramics

The phase structure in the (Ba,Ca)(Ti1−xSnx)O3 lead-free ceramics was evolved from inceptive orthorhombic (O) at 0 ≤ x ≤ 0.04 to a two-phase coexistence of pseudocubic-orthorhombic (PC-O) at 0.06 ≤ x ≤ 0.10 and further to a multiphase coexistence of rhombohedral-pseudocubic-orthorhombic (R-PC-O) at x = 0.11. Due to the multiphase coexistence of R-PC-O at room temperature proved by X-ray diffraction, dielectric constant er and differential scanning calorimetry, an ultrahigh piezoelectric coefficient d33 = 670 pC/N and electrostrain 0.061% were achieved. The high d33 over 520 pC/N was stabilized in a wide compositional range of 0.07 ≤ x ≤ 0.11, suggesting that (Ba,Ca)(Ti,Sn)O3 ceramics are a promising candidate for the lead-free piezoelectric ceramics.

High piezoelectricity due to multiphase coexistence in low-temperature sintered (Ba,Ca)(Ti,Sn)O3–CuOx ceramics

Ultrahigh piezoelectric constant (d33 = 683 pC/N) and converse piezoelectric coefficient (dS/dE = 1257 pm/V) were observed in CuO-doped lead-free (Ba,Ca)(Ti,Sn)O3 ceramics at an optimal composition fabricated by a conventional sintering method at a low temperature 1250 °C. Since all samples showed a pure perovskite structure with coexisting multiphases including cubic, tetragonal, orthorhombic, and rhombohedral phases around two converged triple points, a good compositional stability of high piezoelectricity along with a high d33 and dS/dE over 600 pC/N and 1000 pm/V was achieved within a wide compositional region (1.0 ≤ x ≤ 3.0) regardless of the CuO content (x).

Monodisperse CuS nanodisks: low-temperature solvothermal synthesis and enhanced photocatalytic activity

Controllable synthesis of uniformly disk-shaped CuS nanostructures with a narrow size distribution was realized by a low-temperature (150 °C) solvothermal process using polyvinyl pyrrolidone (PVP) as the surfactant. Monodispersed nanodisks of pure CuS phase with an average diameter of ca. 500 nm could be obtained at a specific S/Cu molar ratio (xS/Cu) of raw materials, which was revealed to affect the phase structure and morphology of the product but the influence of PVP content (xPVP) is limited. The CuS nanodisks have a broad absorption in the visible region and superior photocatalytic performances for the degradation of RhB whose decomposition rate reaches 93% in 2 h, indicating a potential application in the field of wastewater treatment.

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, kp 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 d33 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 d33(E0) and kp exhibit excellent temperature stability behavior as the temperature increases from room temperature to 300 °C.

Multi-phase structure and electrical properties of Bi0.5Li0.5ZrO3 doping K0.48Na0.56NbO3 lead-free piezoelectric ceramics

Abstract(1–x)K0.48Na0.56NbO3–xBi0.5Li0.5ZrO3 (KNN–xBLZ, x = 0–0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method, and their phase structures and electric properties as well as TC were systematically investigated. The orthorhombic–tetragonal (O–T) two phases were detected in all (1–x)K0.48Na0.56NbO3–xBi0.5Li0.5ZrO3 ceramics at 0.01 ≤ x ≤ 0.05. Due to the appropriate ratio between O phase and T phase (CO/CT= 45/55), high piezoelectric properties of d33 = 239 pC/N, kp = 34%, and Pr = 25.23 μC/cm2 were obtained at x = 0.04. Moreover, a high TC = 348°C was also achieved in KNN–xBLZ ceramic at x = 0.04. These results indicate that (1–x)K0.48Na0.56NbO3–xBi0.5Li0.5ZrO3 system is a promising candidate for high-temperature piezoelectric devices.

Modified phase transition and electrical properties of [Li0.05(Na0.535K0.48)0.95]-(Nb0.94Sb0.06)O3 lead-free piezoelectric ceramic by sintering temperature

Li/Sb-doped (Na,K)NbO3 with a nominal composition of [Li0.05(Na0.535K0.48)0.95](Nb0.94Sb0.06)O3 ceramic was synthesized by normal sintering. The phase structure, microstructure, and electrical properties were investigated with a special emphasis on the influence of the sintering temperature. A polymorphic phase transition (PPT) from orthorhombic to tetragonal symmetry was observed when the sintering temperature was raised from 1040 to 1050 °C, whereby the piezoelectric coefficient d33 and the electromechanical coupling coefficient kp reached the peak values of 245 pC·N−1 and 41.2%, respectively. The PPT induced by varying the sintering temperature is due to the different volatilization extents of alkali metals and appears to a lower sintering temperature with increasing Li content. The trace modifying of alkali metal content is more effective than doping B site element to enhance the d33 value.