Search

The KxNa1-xNbO3 nanopowders with cubic-like morphology and an average size of about 50 nm were synthesized by sol-gel auto-combustion method. And then, the ceramics were prepared and the phase transition, microstructure and electrical properties of the KxNa1-xNbO3 ceramics were investigated. Pure perovskite phases of the KxNa1-xNbO3 ceramics were confirmed by XRD patterns and the K0.50Na0.50NbO3 ceramics show the coexistence of orthorhombic and monoclinic structures. SEM micrographs show that all samples have bimodal grain size distributions and the number of the small grains decrease with increasing K+ content in the bimodal grain size distribution system. The K0.50Na0.50NbO3 ceramics with the uniform grain size and the maximum density show excellent electrical properties with er=467.40, tan δ=0.020, d33=128 pC/N and kp=0.32 at the room temperature, demonstrating that the properties of the K0.50Na0.50NbO3 powers prepared by sol-gel auto-combustion are excellent and the ceramics are promising lead-free piezoelectric materials.

The effects of dwell time on the phase structure, microstructure, and electrical properties were investigated for the 0.98(K0.5Na0.5)NbO3-0.02LaFeO3 ceramics (abbreviated as 0.98KNN–0.02LF). All the ceramics sintered for different dwell time are of pure phase and the peak intensity of the 0.98KNN–0.02LF ceramics becomes stronger with a longer dwell time. Denser microstructures with larger grain size are developed for the sample with a longer dwell time. The maximum dielectric permittivity decreases with increasing the dwell time, and the deteriorative dielectric properties are due to the increasing grain size and the domain wall motion. Ferroelectric properties results indicate that 2Pr value slightly decreases with increasing the dwell time, while the 2Ec value increases. Consequently, the 0.98KNN–0.02LF ceramic sintered at 1150 °C for 2 h shows optimum dielectric properties (ɛr=2253 and tan δ

Si/C/B powders were synthesized by carbothermal reduction of xerogels containing boride. Colorless, transparent and monolithic gel was obtained by using tetraethoxysilane, saccharose, tributyl borate, ethanol and distilled water as starting materials. When the xerogel was fired at 1 600 °C in the static argon atmosphere, the XRD pattern commences to show the crystallite peak corresponding with C. β-SiC was synthesized at 1 700 °C, but amorphous remainders could not be eliminated completely. The XRD results show that the boron possibly enters into the silica network, leading to the formation of borosiloxane. Microstructure of β-SiC powders consists of agglomerated particles with diameters ranging from 30 to 100 nm. Though the samples prepared at 1 600 °C and 1 700 °C have better dielectric loss tangent than the sample at 1 500 °C due to exiting crystalline material, the dielectric constant and dielectric loss tangent of three samples reveal lower values.

The piezoelectric ceramics xPb(Mn1/3Sb2/3)O3-(1-x)Pb(Zr1/2Ti1/2)O3 (abbreviated as PMS-PZT) were synthesized by traditional ceramics process. The effect of sintering temperature and the amount of Pb(Mn1/3Sb2/3) O3(abbreviated as PMS) on phase structure, microstructure, piezoelectric and dielectric properties of PMS-PZT ceramics was investigated. The results show that the pure perovskite phase is in all ceramics specimens, the phase structure of PMS-PZT ceramics changes from tetragonal phase to single rhombohedral phase with the increasing amount of PMS. The dielectric constant ɛr, Curie temperature Tc, electromechanical coupling factor kp and piezoelectric constant d33 decrease, whereas the mechanical quality factor Qm and dielectric loss tanδ increase with the increasing amount of PMS in system. The optimum sintering temperature is 1 200–1 250 °C. It is concluded that the PMS-PZT (x=0.07) ceramics sintered at 1 250 °C is suitable for high-power piezoelectric transformer. These properties include ɛr=674.8, tanδ=0.005 25, kp = 0.658, Qm=1 520, d33=230 pC/N, Tc=275 °C.

The lead-free piezoelectric ceramics (l- x (K 0.5 Na 0.5 )NbO 3 - x LiNbO 3 (abbreviated as KNLN) were synthesized by a traditional solid state reaction. The effects of Li + on the sintering characteristic, the phase structure and piezoelectric properties of KNLN ceramics were investigated. The sintering temperature of KNN-based ceramics is decreased by doping Li + and the range of the sintering temperature is narrow. The KNLN ceramics exhibit an enhanced piezoelectric properties with the piezoelectric constant d 33 value of 180-200 pC/N, The electromechanical coupling coefficients k p is 35%-40%. The results show that (l- x )(K 0.5 Na 0.5 )-NbO 3 - x LiNbO 3 ( x =0.05, 0.06) is a promising high-temperature lead free piezoelectric ceramic.

The lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (abbreviated as KNN) with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase structure of KNN ceramics was analyzed. The results show that the pure perovskite phase with orthorhombic symmetry is in all ceramics specimens. The effect of poling conditions on the piezoelectric properties of KNN ceramics was investigated. The results show that the piezoelectric constant d33 and electromechanical coupling factor kp, increase with poling field, poling temperature and poling time increasing, then decrease because of electric broken. Take into account of poling conditions and piezoelectric properties of pure KNN ceramics, the optimum poling conditions for pure KNN ceramics are poling field of 4 kV/mm, poling temperature of 140 °C and poling time of 20–25 min.