Temperature Dependence of Energy Storage Density and Differential Permittivity and Bandgap Study of Relaxor (Pb,La)Zr0.65Ti0.35O3

Abstract: High-performance lead-free thin-film capacitors deposited on the silicon (Si) wafers with large energy storage density (W) and high reliability are strongly attractive in the modern electrical and electronic devices. Here, an ultrahigh W was achieved in the Ba0.3Sr0.7Zr0.18Ti0.82O3 (BSZT) relaxor ferroelectric thin films deposited on the Si wafers with the help of an ultrathin Ca0.2Zr0.8O1.8 (CSZ) artificial “dead-layer” simultaneously possessing high resistivity, wide band gap and high permittivity among linear dielectrics. As the CSZ was implanted, the W of the Ba0.3Sr0.7Zr0.18Ti0.82O3 (BSZT) thin films was greatly increased from 64.9 J/cm3 to 89.4 J/cm3, which is comparable to the best W of thin film deposited on expensive single crystal substrates, and is the largest one reported so far than those of lead-free thin films deposited on the Si wafers, and even for lead thin films. Due to the formation of ultrahigh electrons injection barrier (3.92 eV) between the interface of the CSZ dead layer and the Au top electrode, the Schottky emission of the BSZT thin films under high electric field and at high temperatures was effective suppressed, which is responsible for the greatly improved dielectric breakdown strength and thermal stability. Moreover, the fatigue endurance was also enhanced. It is concluded that the implantation of the CSZ artificial dead-layer could be used as a universal-simple-effective strategy to improve the electrical performances of ferroelectric materials working in the harsh environment of high electric field.

Abstract: In this study, (Pb0.92La0.08) (Zr0.60Ti0.40) O3 (PLZT 8/60/40) ceramics were synthesized using a high-energy ball-milling technique followed by microwave sintering at different temperatures from 900 °C to 1200 °C. The optimal microwave sintering temperature for the PLZT 8/60/40 ceramics was found to be 1150 °C, which is relatively low compared with conventional sintering temperature. The sintered ceramics show the pure perovskite phase, uniform grain microstructure (1.2 µm) and high density (~99.5%). The polarization vs. electric field (P-E) hysteresis curves were used to investigate the ferroelectric and energy storage properties. The switching characteristic in P-E loops and occurrence of domain switching current in current vs. electric field (I-E) loops confirms their ferroelectric nature. The PLZT ceramics, which were sintered at 1150 °C, show the highest remnant polarization (Pr) of ~32.18 μC/cm2 and domain switching current (Imax) of ~0.91 mA with a low coercive field (Ec) of ~10.17 kV/cm. The bipolar and unipolar strain vs. electric field (S-E) hysteresis loops were also measured and the highest unipolar strain was found to be ~0.26% for the PLZT ceramics sintered at 1150 °C. The unipolar S-E curves were used to derive the piezoelectric coefficient (d33~495 pm/V) and a strain hysteresis loss (~5.8%).

Abstract: Transparent ferroelectric ceramic materials suitable for a variety of electrooptic applications were found in the quaternary (Pb,La)(Zr,Ti)O3 system. These PLZT materials are prepared from mixed oxides and hot-pressed typically at 1100°C for 16 h at 2000 psi. Modifying the lead zirconate-titanate system with lanthana linearly reduces the Curie point with increasing lanthana. Transmission measurements in the visible and infrared show that these materials exhibit a nearly constant response from the absorption edge of 0.37 μ to ∼6 μm. The highest transmission values, essentially 100% (neglecting reflection losses of ∼18%) for thin polished plates, were noted for compositions containing 8 at.% La or more. Specific compositions within the system display electrooptic memory or conventional linear or quadratic electrooptic effects; on the basis of the magnitude of the electrooptic effects, they compare quite favorably with single crystals.

Abstract: This review of the PLZT materials and their applications describes the present state of the technology and emphasizes the latest developments in the field of electrooptic ceramics. Despite the reported development of new, transparent materials in other compositional systems, the PLZT's still remain the standard of the industry and continue to find an ever increasing number of applications in the areas of shutters, filters, displays, and spatial light modulators. Their fast response, high resolution and wide operating temperature range make them viable candidates for several emerging technologies including high resolution, non-impact, facsimile printing, electrophotographic copying, color reproduction and integrated optical processing. With the presently successful development of sputtered PLZT thin films, both bulk and thin film PLZT materials can now be considered for future electrooptic devices.

Abstract: A group of transparent ferroelectric hot-pressed (Pb0.92La0.08)-(Zr0.65Ti0.35)0.98O3 specimens with controlled grain size and constant porosity and a group of similar specimens with controlled porosity and constant grain size were prepared. The electrical and optical constants and polarization-reversal properties of these ceramics were determined as functions of grain size and porosity. When poled PLZT ceramics were aged, the polarization-reversal characteristic was quite asymmetric, apparently because a space-charge field, E8p, was generated during aging. From a detailed study of the behavior of the E8p, including its (1) generation with increasing aging time, (2) relaxation with repeated polarization reversals, (3) relaxation by heat depolarization, and (4) grain-size and porosity dependence, it is concluded that the space-charge layer is present inside every domain. This layer also explains the grain-size dependencies of the remanent polarization, piezoelectric constants, and Curie point.

Abstract: The electrocaloric effect (ECE) in inorganic thin film and organic relaxor ferroelectrics is investigated by directly measuring the ECE around room temperature. The results reveal that giant ECEs can be obtained in the high energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) relaxor copolymer and in the La-doped Pb(ZrTi)O3 relaxor ceramic thin films, which are much larger than that from the normal ferroelectric counterparts. The large ECE observed, compared with normal ferroelectrics, is likely caused by the large number of disordered fluctuating polarization entities in relaxor ferroelectrics which can lead to extra entropy contributions and larger ECE.

Abstract: The dielectric dispersion of the transparent relaxor ferroelectric ceramics PLZT 8/65/35 and 9.5/65/35 was determined in a wide frequency range including the microwave and infrared range. The number of observed polar phonons in infrared spectra gives evidence about the locally broken cubic symmetry and the presence of polar nanoclusters in the whole investigated temperature range up to 530 K. A single broad and symmetric dispersion that occurs below the polar phonon frequencies was fitted with the Cole-Cole formula and a uniform distribution of Debye relaxations. On decreasing temperature, the distribution of relaxation times becomes extremely broad which indicates increasing correlation among the clusters. The mean relaxation time diverges according to the Vogel-Fulcher law with the same freezing temperature 230±5 K for both ceramics, but different activation energies 1370 K and 1040 K for the 8/65/35 and 9.5/65/35 sample, respectively. The shortest relaxation time is about 10-12 s and remains almost temperature independent. Below room temperature, the loss spectra become essentially frequency independent and the permittivity increases linearly with decreasing logarithm of frequency. The slope of this dependence is proportional to T 4 in the investigated temperature range (above 210 K) which indicates appreciable anharmonicity of the potential for polarization fluctuations.