Key Engineering Materials Vols. 336-338

Abstract: Effect of co-doping two different elements and incorporating SrBi2Nb2O9 (SBN) on structure and field-stability of dielectric properties in PMNT ceramics were investigated. Single-phase cubic Perovskite structure is more easily obtained by appropriate co- doping of La3+ and Zn2+. X-ray diffraction patterns of PMNT/SBN composite showed that there is no SBN grains in PMNT/SBN as a secondary phase. Co-doping of La3+ and Zn2+ as well as incorporation of SBN markedly increased the field-stability of dielectric constant. The mechanism of improving field-stability was tentatively discussed.

Abstract: In present work, sol-gel process is used to direct the organization of high quality and pore-free parasite PZT thin films with a composition near the morphotropic phase boundary (Zr/Ti = 52/48). The PZT transparent sol can be obtained by dissolving the zirconium oxynitrate, butyl titanate and lead acetate in ethylene glycol with the molar ratio of 0.52:0.48:1 and the PZT gel can be gained by spin-coating. In such process, PZT thin films can be readily prepared by hydrolysis on hot plate at 350°C for 20min and annealing in RTA at 650°C for 1 minute. The structural and electric characteristics of the films have been carried out by XRD, AFM and the C-V measurements, etc. Experimental results have indicated that by treating film RTA at 6508 for 1 minute film with perfect crystallization and good surface morphology with a RMS roughness of 2.0nm can be obtained, and the remnant polarization Pr (28.5 μC/cm2) and coercive field Ec (39.8kV/cm) are obtained in the P-E hysteresis loops. The films have a dielectric constant ε of 1080 and a dielectric loss tanδ of 0.01 at 1 kHz. Ferroelectric polarization fatigue test of the films has shown that high fatigue resistance up to 3 × 1010 cycles before Pr is decreased by 50%.

Abstract: The dielectric response of [110]-oriented 0.68PMN-0.32PT single crystal under dc electric field has been investigated. The characteristics of phase transition under temperature and dc electric field are provided. When electric field is above 2.3kV/cm, abnormal phase transition is induced by temperature and electric field, which corresponds to the phase transition from rhombohedral to orthorhombic ferroelectric phase. With increasing dc electric field, the stable temperature region of orthorhombic phase is expanded. The electric field-temperature (E-T) phase diagram of [110]-oriented 0.68PMN-0.32PT single crystals is presented. The polarization rotation in [110]-oriented single crystal is discussed.

Abstract: Without addition of any thermodynamically stable perovskite compound such as PbTiO3, Pb(Mg1/3Nb2/3)O3 was fabricated by a new sol-gel route, and the processing parameter was studied. The result showed that the chelating effect of ammonium citrate was relatively better than that of citric acid in this system. When the ratio of ammonium citrate to Nb2O5 was 8.33, the colloid of Nb2O5·nH2O was in state of transparency. The effects of heat treatment on the formation of perovskite phase of Pb(Mg1/3Nb2/3)O3 powders were characterized by X-Ray Diffraction (XRD) method. With increasing heat treatment temperature or holding time, pyrochlore phase turned into perovskite phase gradually, and after second calcination, the content of perovskite phase increased significantly from 54% to 72%.

Abstract: Ferroelectric properties of (Bi1/2Na1/2) TiO3-SrTiO3 were studied. The dielectric properties were measured at 1KHz. It was found that the dielectric constants are improved with the increase of additive amount of BNT. If the amount continues increasing, the properties become worse, the optimum dielectric constant of the samples can reach 4300. When the proportion of (Bi1/2Na1/2)TiO3: SrTiO3 is 65:35, with the increase of additive amount of MnCO3, the Curie temperature descends obviously. The dielectric constant increased at beginning and dropped sharply when the amount of MnCO3 exceeds 1.1wt%.

Abstract: Microstructure and dielectric properties of Ba0.62Sr0.38TiO3 ceramics doped with x mol% (x=0.2~0.6) Y2O3 were investigated. SEM showed that Y3+ can accelerate growth of the grains at first, then turn to inhabit growth of the grains with further addition of Y3+ above 0.8mol%. The experimental results showed that the dielectric constants were improved with the additive amount of Y3+ increasing, if the amount of Y3+ increased continuously, the dielectric constants will drop, whereas the dielectric losses of the samples descended rapidly in the beginning, then went up obviously with further addition of Y3+ above 1.0mol%, the optimal dielectric constant and dielectric loss could reach 6700 and 0.0015 in the room temperature, respectively.

Abstract: A lead-free piezoelectric ceramic ternary system based on (Bi0.5Na0.5)TiO3 (BNT)-(Bi0.5 K0.5)TiO3(BKT)-BaTiO3(BT) near the morphotropic phase boundary (MPB) between the tetragonal and rhombohedral phases has been investigated. The samples were prepared by a conventional sintering technique. Piezoelectric properties, dielectric properties and microstructures of BNT-BKT-BT lead-free piezoelectric ceramic were studied. The X-ray diffraction (XRD) patterns show that the ceramics possess a single-phase perovskite structure. The measurements of piezoelectric properties reveal that this system has a relatively high piezoelectric performance: the piezoelectric constant d33 reached to 178pC/N and planar electromechanical coupling factor kp enhanced to 0.325. The BNT-BKT-BT ternary system ceramics could be well sintered at 11500C with a high-density ratio of more than 95% of the theoretical density.

Abstract: Pb(Mg1/3Nb2/3)O3-PbTiO3 based ceramics were produced by conventional sintering method and their electric-field induced electromechanical properties were determined. Large fieldinduced electromechanical coupling factors, with high piezoelectric anisotropy, were obtained in this relaxor material at relatively low DC electric bias field. A circular ultrasonic transducer with non uniform radial induced polarization was constructed using this material for field diffraction control.

Abstract: 1wt% CuO-TiO2 (molar ratio, CuO/TiO2= 1) mixture is added as the liquid phase sintering aid to develop the sintering and dielectric characteristics of (Ba1-xSrx)TiO3 (x=0, 0.1, and 0.2) ceramics. The crystal characteristics of calcined (Ba1-xSrx)TiO3 powders and sintered (Ba1-xSrx)TiO3 ceramics are developed by using X-ray diffraction method. The calcined (Ba1-xSrx)TiO3 powders and 1050oC-sintered (Ba1-xSrx)TiO3 ceramics reveal a tetragonal or pseudo-cubic structure and the 1150oC-sintered(Ba1-xSrx)TiO3 ceramics reveal a tetragonal structure. Sintered at 1100oC, the (Ba1-xSrx)TiO3 ceramics present a porous structure; Sintered at 1150oC, the (Ba1-xSrx)TiO3 ceramics present a uniform growth. The grain size decreases with the increase of SrO content. In this study, the dielectric characteristics of CuO-TiO2 mixture-fluxed (Ba1-xSrx)TiO3 ceramics are also developed.

Abstract: The influence of processing parameters on the morphology of hydrothermally derived BaTiO3 powders was investigated. Layered H2Ti3O7 with plank-like morphology were used as the Ti-precursor materials. The BaTiO3 powders were characterized by XRD and SEM. Lower Ba/Ti ratio is benefit for preparation of BaTiO3 particles which retains the morphology of the precursor. The BaTiO3 particles obtained at 200°C for 24h were large, uniform, and plank-like particles. Extending the hydrothermal temperature or the hydrothermal time does not help to synthesize BaTiO3 powders of large size and uniform morphology.