Ningxin Zhang

Frequency dependence of ferroelectric fatigue in PLZT ceramics

Electric induced fatigue in ferroelectric PLZT ceramics was investigated. The fatigue occurred with the increasing of accumulative switching cycles in samples. The polarization decreased with the development of fatigue. At the same time, the piezoelectric properties also degraded during the process of ferroelectric fatigue. The different fatigue behaviors were observed in PLZT ceramics when processed under different frequencies of applied electric field, despite the same magnitude. The samples can be easily fatigued at low frequency while hardly fatigued at high frequency. The phenomenon was explained according to the dynamic behavior of ferroelectric domains during their responce to the applied electric field.

Interfacial reaction of Ag/Pd metals with Pb-based relaxor ferroelectrics including additives

Abstract In order to effectively control the interfacial reactions during co-firing a multilayer ceramic device (MLCD), different effects of silver/palladium on Pb-based relaxor ferroelectric ceramics were investigated by means of a series of powder X-ray diffraction (XRD) spectra and chemical reaction thermodynamics. It is found that the reaction kinetics of palladium and Pb-based relaxor ceramics lies in the activity of palladium and the structural stability of relaxor ferroelectric ceramics. In this respect, silver can decrease the activity of palladium so that a less serious interfacial problem exists in a MLCD with 30Pd/70Ag electrodes. Moreover, BaTiO 3 and SrTiO 3 ceramic additives were found to effectively suppress Pd-PNN reactions because of increasing the structural stability of PNN. It is pointed out that the addition of BaTiO 3 or SrTiO 3 ceramic powders into the dielectric layers and particularly into the inner electrode pastes may play dual roles, including modifying the densification mismatch and preventing the interfacial reactions between the electrodes and the dielectric layers.

Preparation and properties of PLZT thick films on silicon

Abstract Lead-lanthanum-zirconate-titanate (PLZT) thick films were prepared on Pt/Ti/SiO 2 /Si substrates with PZT/PT seeding layer by the screen-printing method. Phase characterization and crystal orientation of the PLZT thick films were investigated by X-ray diffraction analysis (XRD). The ferroelectric hysteresis loop, high-frequency dielectric constant, dielectric loss and piezoelectric constant of the PLZT thick films were measured. The remnant polarization of the silicon-based PLZT thick films was about 32 μC cm −2 , the coercive field was about 20 kV cm −1 and the piezoelectric constant d 33 was about 630 pC N −1 . In the frequency range from 1 to 300 MHz, the dielectric constant was about 3000 and the dielectric loss was less than 0.03, respectively. The PLZT thick films with excellent ferroelectric, high frequency and force–electric coupling properties should be suitable for the ferroelectrics–silicon integrated system, and be a good candidate material for the third-generation (3G) mobile communication and the force–electric coupling microelectromechanical system (MEMS) device applications.

High-frequency properties of PZT for RF-communication applications

Abstract Lead–zirconate–titanate (PbZr 0.53 Ti 0.47 O 3 ) nano powders and ceramics were prepared using a sol–gel method. Phase characterization of the lead–zirconate–titanate (PZT) material was identified by X-ray diffraction analysis (XRD). Micro-structure of the samples was examined by the scanning electron microscopy (SEM). Ferroelectric hysteresis loop, high-frequency dielectric response and piezoelectric constant d 33 were measured. The remnant polarization ( P r ) of the PZT ceramics pellet is about 20 μC cm −2 and the coercive field ( E C ) is about 30 kV cm −1 . The dielectric constant is about 900 and the dielectric loss is lower than 0.02 in the radio-frequency (RF) region. The piezoelectric constant d 33 is about 170 pC N −1 . The experimental results show that the PZT material can be suitable for the applications of miniature RF front-end devices and force-electric coupling devices.

Non-destructive investigation of microstructure evolution due to ferroelectric fatigue in PLZT ceramics

The fatigue properties of rhombohedral Pb0.94La0.04(Zr0.60Ti0.40)O3 ferroelectric ceramic under alternate electric field were investigated. During fatigue process, switchable polarization of ferroelectric sample decreased with the accumulative switching of ferroelectric polarization. The microstructure evolution before and after fatigue experiments was investigated via X-ray diffraction. Compared to the X-ray diffraction pattern of sample at original state, decrease of characteristic diffraction peak strength was observed in the diffraction pattern of sample after about 107 cycles of polarization reorientation, as well as the split of diffraction peak at high diffraction angle. The split of diffraction peaks in rhombohedral phase PLZT ceramics indicated that microstructure in ferroelectric bulks had underwent changes and textured ferroelectric domains were formed due to the compromise between electric and mechanical energy after repetitive reorientation of ferroelectric polarization, which resulted in the concentrated internal stress and was suggested as a mechanism of ferroelectric fatigue.

Improvement of electric fatigue in PLZT ferroelectric capacitors due to zirconia incorporation

Abstract Fatigue properties induced by cyclic electric loading in PLZT capacitors incorporating zirconia were investigated. The improvement of fatigue properties was achieved with increasing the amount of incorporated zirconia. During the fatigue process, the onset of fatigue, which is characterized by the fast decrease of switchable polarization, was delayed in composite PLZT/zirconia, compared to the monolithic PLZT samples. After about 106 polarization reverse cycles in composite samples, the capacitors seemed to show no sign of deterioration in saturated or remanent polarization. A higher resistivity was observed in the PLZT/zirconia compared to monolithic PLZT ceramics during the measurement of complex ac impedance spectroscopy. According to the dynamic behavior of oxygen vacancies during the electric switching process, the mechanism of enhancement of the fatigue properties was attributed to the low content of oxygen vacancies in bulk ceramics and less pinning effect to ferroelectric domain walls.

Degradation of piezoelectric and dielectric relaxation properties due to electric fatigue in PLZT ferroelectric capacitors

The fatigue properties of ferroelectric ceramics due to electric loading were investigated. With the decrease of switchable polarization, the piezoelectric and dielectric relaxation properties were both found to be deteriorated heavily. The G-B circles decreased to a smaller one indicating the weakening of piezoelectric resonance. The measurement of complex impedance showed that the bulk resistance also degraded after fatigue with the decreasing of relaxation time. Oxygen vacancy was believed to be responsible for the fatigue properties by analyzing the activation energy variation. The mechanism for fatigue was suggested according to the possible relationship between the degradation of piezoelectric and dielectric properties.

Multilayer piezoelectric ceramic transformer with low temperature sintering

The low-fired high performance piezoelectric ceramics used for multilayer piezoelectric transformer were investigated. Based on the transient liquid phase sintering mechanism, by doping suitable eutectic additives and optimizing processing, the sintering temperature of the quaternary system piezoelectric ceramics with high piezoelectric properties could be lower to about 960–1000°C. The low-temperature sintering multilayer piezoelectric transformer (MPT) has been developed. Some characteristics of MPT were systemically studied. The measurements include the frequency response of input impedance, frequency response of phase difference between input voltage and current, frequency shifting with load, input impedance changing with load, phase difference between input voltage and current shifting with load, and phase difference between input voltage and vibration velocity. The vibration modes and resonance characters of MPT were measured by a Laser Doppler Scanning Vibrometer. Several kinds of MPT with high voltage step-up ratio, high power density, high transfer efficiency and low cost have been industrially produced and commercialized. It reveals a broad application prospect for back-light power of liquid crystal display and piezo-ionizer etc.

Improvement of electric fatigue properties in Pb0.94La0.04(Zr0.70Ti0.30)O3 ferroelectric capacitors due to SrBi2Nb2O9 incorporation

The influences of SrBi2Nb2O9 (SBN) on dielectric and ferroelectric properties of (PLZT) ceramics were systematically investigated. X-ray diffraction patterns of PLZT/SBN composite showed that there was no chemical reaction between PLZT and SBN in all cases. SEM pictures on the fracture section revealed a transformation from the transgranular to the intergranular mode with the increase of SBN content in composites. An abnormal and interesting increase of dielectric constant was observed after the incorporation of SBN in PLZT bulks, which could not be explained via the mixing law of dielectrics. Although it turned to be a little shrinkage, hysteresis loops still kept well-formed shapes in PLZT/SBN composites. Compared with the serious degradation of switchable polarization in pure PLZT sample after repeated polarization switching, no apparent decrease of switchable polarization strength was found in PLZT/SBN composites. The improvement mechanism of electric fatigue endurance in PLZT ceramics after SBN incorporation was attributed to the facilitation of oxygen vacancies’ mobility in the bismuth oxide layer in SBN.

Improvement of electric fatigue properties in PLZT ferroelectric ceramics due to SrBi2Ta2O9 incorporation

Abstract The influences of SrBi 2 Ta 2 O 9 (SBT) on dielectric and ferroelectric properties of Pb 0.94 La 0.04 (Zr 0.70 Ti 0.30 )O 3 ceramics were investigated systematically. X-ray diffraction (XRD) patterns of PLZT–SBT composite showed that there was no chemical reaction between PLZT and SBT. SEM pictures on fracture section reflected a main transgranular fracture mode. An abnormal and interesting increase of dielectric constant was observed after SBT incorporation. Hysteresis loops of PLZT–SBT composites turned to slimmer shape with the increase of SBT content. No apparent decrease of switchable polarization strength was found in PLZT–SBT composites after repeated polarization switching. HRTEM picture of SBT grain in PLZT–SBT composite revealed a transformation from order to disorder near the tip of grain boundary as well as low angle of grain boundary, which could release concentrated internal stress and served as improvement mechanism of electric fatigue endurance in PLZT–SBT composites.