Key Engineering Materials Vols. 336-338

Abstract: Fine-scale 1-3 PZT/epoxy piezoelectric composites were prepared by a dice-fill process, and their resonance characteristics and dynamic piezoelectric properties were investigated. The resonance characteristic was deeply influenced by PZT volume fraction and the thickness of 1-3 PZT/epoxy composite. The experiments proved that reducing the distance between PZT rods and/or increasing the height/width ratio could weaken the additional coupling effect of lateral resonance mode on thickness mode. The PZT/epoxy composites displayed only thickness-mode resonance when the distance between PZT rods was reduced to 220μm and its aspect ratio was increased up to 10.

Abstract: The effects of A-site cation size disorder in ABO3 type ferromagnetic metallic La0.55Ca0.45MnO3 system have been studied by substituting La3+ and Ca2+ by other ions, while keeping the valency of Mn ions and the A-site cation mean radius constant in the substituted compounds with different A-site ionic radii variance σ2 = Σi (xiri 2 − 2), where xi and ri are the atomic fraction and ionic radii of i-type ions at A-site, respectively. It is revealed that the A-site disorder induces the decreasing of the magnetization and the increasing of the resistivity. The ferromagnetic Curie point TC decreases with the increasing of the A-site ionic radii variance, too. Moreover, the ground state of the system transits from ferromagnetic metal to glass insulator upon increasing variance of the A-site ionic radii from 0.0003 for La0.55Ca0.45MnO3 to 0.009 for Gd0.55Sr0.45MnO3. It is argued that the suppression of the ferromagnetism is ascribed to the enhanced radial distortion of the MnO6 octahedra due to the increasing A-site disorder.

Abstract: Electric fatigue of piezoelectric ceramics is very important for piezoelectric actuator applications in strong field. In order to classify the fatigue of ferroelectric and piezoelectric properties, the electric fatigue behavior of piezoelectric ceramics of PZT-PMN-PNN was investigated under bias and unipolar pulse cycling field. The bias and unipolar polarization hysteresis loops are measured before and after cycling. The polarization measurements after cycling show a much smaller decrease than bipolar fatigue, but the piezoelectric coefficient d33 still suffers relatively higher deterioration, which indicates different characteristics for piezoelectric and ferroelectric fatigues. A possible mechanism of the partial pining of switching domains responsible for the difference is discussed in this paper.

Abstract: Bipolar electric fatigue in ferroelectric niobium-doped lead zirconate titanate stannate ceramics was investigated. Variations in the polarization and strain hysteresis loops as well as microstructural modifications of the material due to the electric cycling were analyzed. Compared with ferroelectric PZT ceramics cycled under similar conditions, the material exhibited a higher resistance to electric fatigue. Properties of the specimens showed significant decays above 106.5 cycles. Asymmetric suppression of strain hysteresis loop was monitored. At 108 cycles, the remanent polarization, the right maximum strain and the left maximum strain decreased to 70%, 58% and 44% of their initial values, respectively. The color of the material was changed from pale yellow to dark grey with cycling. The properties and color of the fatigued samples were recovered almost fully to those of the virgin state after a heat treatment at 500oC for 1 h. The pinning of domain walls, probably by oxygen vacancies, was concluded to be the predominant fatigue mechanism for the material.

Abstract: Propagation and deflection of microcracks driven by electric loading in <001>-oriented 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 ferroelectric single crystals were investigated using an in-situ transmission electron microcopy (TEM) technique. The static observation of the domain pattern revealed the coexistence of sub-micrometer and nano-meter domains. Electric field induced deviation from the main microcrack path and subsequent propagation along the direction almost perpendicular to the electric field were observed directly. A qualitative analyses is given based on the maximum energy release rate criterion.

Abstract: A comparison experiment was conducted in which some lead zirconate titanate (PZT) piezoelectric ceramic rings were simply immersed in a 0.01 M NaOH solution while other PZT rings were immersed in the solution with a 50 Hz AC voltage applied between the electrodes of the rings and a counter electrode in the solution. Though the simple immersion showed no noticeable influence on the PZT rings, those PZT rings treated with the application of the AC voltage were obviously degraded in their piezoelectric properties. It was proposed that the degradation resulted from the collaborated reactions of atomic hydrogen and oxygen generated in the AC voltage-induced electrolysis of water. Water may be an important origin for degradation of piezoelectric ceramic devices operating under AC voltages.

Abstract: Degradation aging of BaTiO3 microwave ceramic capacitors for EMI applications at highvoltage, AC 10kV, was focused in this paper. Electric performances of the ceramic capacitors were systematically evaluated with thermal shock (5 cycles of –30 °C for 1 h and then 125°C for 1 h), damp heat (100% RH at 40°C for 500 h), and, endurance at high temperature (DC 10 kV at 100°C for 500 h). High reliability for the ceramic capacitor was obtained with optimal ceramic composition, sintering temperature, epoxy resin, curing agent and additives, which was satisfied with practical microwave technologies.

Abstract: Ba0.6Sr0.4TiO3 (BST) thin films deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering and crystallized by rapid thermal annealing (RTA) exhibit much thinner BST/Pt interfacial transition layer and higher dielectric properties than the films crystallized by conventional thermal annealing (CTA). HRTEM observations show that the transition layer is 2-3nm thick for RTA and 4-5nm thick for CTA. XPS investigations display that the transition layer is composed of perovskited BST phase and non-perovskited BST phase, and RTA corresponds to much less non-perovskited BST phase than CTA. The reason for non-perovskited BST phase and the dielectric properties of BST films are also presented.

Abstract: A series of ferrroelectric-ferromagnetic composites were synthesized from BaTiO3 and NiFe2O4 ferrite by conventional solid-state route. XRD studies indicated that the composites comprised of only two phases, BaTiO3 phase with perovskite structure and NiFe2O4 phase with spinel structure. Frequency dependence of permittivity and permeability were also measured. Experimental results showed that the dielectric constant and initial permeability of these composites could be tunable by varying the composition of composites. Thus, these composites can be used for multilayer chips EMI filters.

Abstract: Ferroelectric PZT heterolayered thick films were fabricated by the alkoxide-based sol-gel method. PZT(20/80) and PZT(80/20) paste were made and alternately screen-printed on the alumina substrates. The coating and drying procedure was repeated 4 times to form the heterolayered thick films. The thickness of the PZT heterolayered thick films was approximately 60 μm. All PZT thick films showed the typical XRD patterns of a perovskite polycrystalline structure. The relative dielectric constant and the dielectric loss of the PZT thick films sintered at 1050oC were 283 and 1.90%, respectively.