PZT, processing

Generally speaking, at least for PZT processing, hydrolysis and catalysis conditions display similar effects to those noted for the silica system, but the supporting experimental evidence is not as well developed. 

Yi G, Sayer M, Wu Z. An acetic acid/water based sol-gel PZT process I modification of Zr and Ti aUcoxides with acetic acid. J Sol-Gel Sci Technol 1996 6 65-74. 

Yi G., Sayer M. An acetic acid/water based sol-gel PZT process I modification ofZr and Ti alkoxides with acetic acid. J. Sol-Gel Sci. Technol. 1996a 6 65-74 Yi G., Sayer M. An acetic acid/water based sol-gel PZT process II formation of a water based solution. 1. Sol-Gel Sci. Technol. 1996b 6 75-82 Yoldas B.E. Hydrolysis of aluminium alkoxides and bayerite conversion. J. Appl. Chem. Biotechnol. 1973 23 803-809... 

Calcination. Calcination involves a low (<1000° C) temperature soHd-state chemical reaction of the raw materials to form the desired final composition and stmcture such as perovskite for BaTiO and PZT. It can be carried out by placing the mixed powders in cmcibles in a batch or continuous kiln. A rotary kiln also can be used for this purpose to process continuously. A sufficiendy uniform temperature has to be provided for the mixed oxides, because the thermal conductivity of powdered materials is always low. 

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

Solution deposition processing has been used to prepare thin films (qv) of PbTiOg, PZT, PLT, PLZT, BaTiO, LiNbOg, PMN, PMN-PT,... 

Ferroelectric Thin-Film Devices. Since 1989, the study of ferroelectric thin films has been an area of increasing growth. The compositions studied most extensively are in the PZT/PLZT family, although BaTiO, KNbO, and relaxor ferroelectric materials, such as PMN and PZN, have also been investigated. Solution deposition is the most frequentiy utilized fabrication process, because of the lower initial capital investment cost, ease of film fabrication, and the excellent dielectric and ferroelectric properties that result. 

These lead-based materials (PZT, PLZT, PMN) form a class of ceramics with either important dielectric, relaxor, pie2oelectric, or electrooptic properties, and are thus used for appHcations ia actuator and sensor devices. Resistive properties of these materials ia film form mirror the conduction processes ia the bulk material. Common problems associated with their use are low dielectric breakdown, iacreased aging, and electrode iajection, decreasiag the resistivity and degrading the properties. 

Figure 2.1. Processing stages in chemical solution deposition of thin films. Controllable parameters are shown on the left dependent processes are shown in italics. [Reprinted from Ref. 16 with the permission of the publisher, Taylor Francis, Ltd. R. W. Schwartz et al., Sol-gel processing of PZT thin films a review of the state-of-the-art and process optimization strategies, Int. Ferro., 7,259, (1995).]...

Figure 2.14. SEM photomicrographs of (a) poorly and (b) effectively processed 0.95 PbZrO3-0.05 PbTi03 (PZT 95/5) thin films. [Reprinted with permission from Ref. 9. Copyright 1997 American Chemical Society.]...

Schwartz, R. W. Assink, R. A. Headley, T. J. 1992. Solution chemistry effects in PZT thin film processing spectroscopic and microstructural characterization. In Ferroelectric Thin Films II, edited by Kingon, A. I. Myers, E. R. Tuttle, B. Mat. Res. Soc. Symp. Proc. 243 245-254. 

Lakeman, C. D. E. Guistolise, D. J. Tani,T. Payne, D. A. 1994. Effect of thermal processing conditions on the structure and properties of sol-gel derived PZT thin layers. Br. Ceram. Proc. 52 70-76. 

Lipeles, R. A. Coleman, D. J. 1988. Effect of drying and annealing on metallo-organic solution deposition of PZT films. In Ultrastructure Processing of Advanced Ceramics, edited by Ulrich, D. R. Mackenzie, J. D. John Wiley Sons, Inc., New York. pp. 919-933. 

This 4 Mb FRAM utilizes lead zirconate titanate (PZT) as the active memory element a similar prototype has been made by Matsushita/Panasonic using strontium bismuth tantalate (SET). A 32-Mb SET memory has more recently been announced by Samsung. Device performances are similar in each case. The PZT device has the advantage that it can be processed at lower temperatures (450 °C, compared with ca. 650 °C for SET) the SET devices have the environmental advantage that they are lead-free. 

In contrast to piezoelectric single crystals, such as quartz, the piezoelectricity of PZT ceramics decays with time due to relaxation. Experimentally it is found that on a large time scale (for example, months and years), the aging process can be accurately described by a logarithmic law. For example, the coupling constant k varies with time f as... 

Barium titanate is one example of a ferroelectric material. Other oxides with the perovskite structure are also ferroelectric (e.g., lead titanate and lithium niobate). One important set of such compounds, used in many transducer applications, is the mixed oxides PZT (PbZri-Ji/Ds). These, like barium titanate, have small ions in Oe cages which are easily displaced. Other ferroelectric solids include hydrogen-bonded solids, such as KH2PO4 and Rochelle salt (NaKC4H406.4H20), salts with anions which possess dipole moments, such as NaNOz, and copolymers of poly vinylidene fluoride. It has even been proposed that ferroelectric mechanisms are involved in some biological processes such as brain memory and voltagedependent ion channels concerned with impulse conduction in nerve and muscle cells. 

As discussed in Section 5.7.2, in the case of niobium-containing perovskites it is necessary to avoid the formation of pyrochlore-type phases if reproducible and optimum dielectric and piezoelectric properties are to be achieved. G. Roberts et al. [13] developed a modification of the B-site precursor ( columbite process) route to produce high quality PNN-PZT ceramics. 

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