Lead titanate , piezoelectric properties

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). 

Lead zirconate [12060-01 -4] PbZrO, mol wt 346.41, has two colorless crystal stmctures a cubic perovskite form above 230°C (Curie point) and a pseudotetragonal or orthorhombic form below 230°C. It is insoluble in water and aqueous alkaUes, but soluble in strong mineral acids. Lead zirconate is usually prepared by heating together the oxides of lead and zirconium in the proper proportion. It readily forms soHd solutions with other compounds with the ABO stmcture, such as barium zirconate or lead titanate. Mixed lead titanate-zirconates have particularly high piezoelectric properties. They are used in high power acoustic-radiating transducers, hydrophones, and specialty instmments (146). 

Alkaline-Earth Titanates. Some physical properties of representative alkaline-earth titanates ate Hsted in Table 15. The most important apphcations of these titanates are in the manufacture of electronic components (109). The most important member of the class is barium titanate, BaTi03, which owes its significance to its exceptionally high dielectric constant and its piezoelectric and ferroelectric properties. Further, because barium titanate easily forms solid solutions with strontium titanate, lead titanate, zirconium oxide, and tin oxide, the electrical properties can be modified within wide limits. Barium titanate may be made by, eg, cocalcination of barium carbonate and titanium dioxide at ca 1200°C. With the exception of Ba2Ti04, barium orthotitanate, titanates do not contain discrete TiO ions but ate mixed oxides. Ba2Ti04 has the P-K SO stmcture in which distorted tetrahedral TiO ions occur. 

Zirconate compounds exhibit several interesting properties. Lead zirconate—titanate [12626-81 -2] compositions display piezoelectric properties which are utilized in the production of EM-coupled mode filters, resonators in microprocessor clocks, photoflash actuators, phonograph cartridges, gas... 

Lead titanate (PbTi03) is a ferroelectric material with unusual pyroelectric and piezoelectric properties. It is deposited by MOCVD from ethyl titanate and lead vapor in oxygen and nitrogen at 500-800°C.[42]... 

Lead titanate (PbTiOg) with excellent pyroelectric and piezoelectric properties. 

Jaffe, B., Roth, R. S., and Marzullo, S. (1954). Piezoelectric properties of lead zirconate-lead titanate solid-solution ceramics. J. Appl. Phys. 25, 809-810. 

Electroceramics. Titanates like barium, strontium, calcium and lead titanate prepared from finely divided, high-purity TiOz hydrolysates are used in capacitors, PTC-resistors and piezoelectric materials. The specifications of the Ti02 starting materials with respect to purity, reactivity, and sintering properties are expected to become more stringent. The market is estimated to be several thousand of tonnes a year as TiOz. A strong annual growth is expected. 

We show in Figure 13.8 that in the case of a well-behaved piezoelectric relaxation (counterclockwise hysteresis) presented in Figure 13.7, the Kramers-Kronig relations are indeed fulfilled. Closer inspection of the data show that the relaxation curves can be best described by a distribution of relaxation times and empirical Havriliak-Negami equations [19]. It is worth mentioning that over a wide range of driving field amplitudes the piezoelectric properties of modified lead titanate are linear. Details of this study will be presented elsewhere. 

Ferroelectric ceramics (such as barium titanate, lead zircanate titanate) Sensors and actuators, electronic memory, optical applications Tape casting, sputtering, pressing, templated grain growth Improved dielectric and piezoelectric properties... 

Pyro- and Piezoelectric Properties The electric field application on a ferroelectric nanoceramic/polymer composite creates a macroscopic polarization in the sample, responsible for the piezo- and pyroelectricity of the composite. It is possible to induce ferroelectric behavior in an inert matrix [Huang et al., 2004] or to improve the piezo-and pyroelectricity of polymers. Lam and Chan [2005] studied the influence of lead magnesium niobate-lead titanate (PMN-PT) particles on the ferroelectric properties of a PVDF-TrFE matrix. The piezoelectric and pyroelectric coefficients were measured in the electrical field direction. The Curie point of PVDF-TrFE and PMN-PT is around 105 and 120°C, respectively. Different polarization procedures are possible. As the signs of piezoelectric coefficients of ceramic and copolymer are opposite, the poling conditions modify the piezoelectric properties of the sample. In all cases, the increase in the longitudinal piezoelectric strain coefficient, 33, with ceramic phase poled) at < / = 0.4, the piezoelectric coefficient increases up to 15 pC/N. The decrease in da for parallel polarization is due primarily to the increase in piezoelectric activity of the ceramic phase with the volume fraction of PMN-PT. The maximum piezoelectric coefficient was obtained for antiparallel polarization, and at < / = 0.4 of PMN-PT, it reached 30pC/N. 

Piezoelectricity links the fields of electricity and acoustics. Piezoelectric materials are key components in acoustic transducers such as microphones, loudspeakers, transmitters, burglar alarms and submarine detectors. The Curie brothers [7] in 1880 first observed the phenomenon in quartz crystals. Langevin [8] in 1916 first reported the application of piezoelectrics to acoustics. He used piezoelectric quartz crystals in an ultrasonic sending and detection system - a forerunner to present day sonar systems. Subsequently, other materials with piezoelectric properties were discovered. These included the crystal Rochelle salt [9], the ceramics lead barium titanate/zirconate (pzt) and barium titanate [10] and the polymer poly(vinylidene fluoride) [11]. Other polymers such as nylon 11 [12], poly(vinyl chloride) [13] and poly (vinyl fluoride) [14] exhibit piezoelectric behavior, but to a much smaller extent. Strain constants characterize the piezoelectric response. These relate a vector quantity, the electrical field, to a tensor quantity, the mechanical stress (or strain). In this convention, the film orientation direction is denoted by 1, the width by 2 and the thickness by 3. Thus, the piezoelectric strain constant dl3 refers to a polymer film held in the orientation direction with the electrical field applied parallel to the thickness or 3 direction. The requirements for observing piezoelectricity in materials are a non-symmetric unit cell and a net dipole movement in the structure. There are 32-point groups, but only 30 of these have non-symmetric unit cells and are therefore capable of exhibiting piezoelectricity. Further, only 10 out of these twenty point groups exhibit both piezoelectricity and pyroelectricity. The piezoelectric strain constant, d, is related to the piezoelectric stress coefficient, g, by... 

Two common piezoelectric materials are polymers (polyvinylidene fluoride, PVDF) and c mics (lead zirconate titanate, PZT). The polymer materials are soft and flexible however have lower dielectric and piezoelectric properties than ceramics. Conventional piezoelectric ceramic materials are rigid, heavy and can only be produced in block form. Ceramic materials add additional mass and stiffiiess to the host structure, especially when working with flexible/lightweight materials. This and their fragile nature limit possibilities for wearable devices. Comparisons of several piezoelectric materials are presented in Table 1. 

Du, X.H., Belegundu, U., and Uchino, K. (1997) Crystal orientation dependence of piezoelectric properties in lead zirconate titanate theoretical expectations for thin films. Jpn. J. Appl. Phys., 36 (9A), 5580-5587. Reprinted with permission from American Institute of Physics. 

Li Z, Grimsditch M, Xu X, Chan SK (1993) The elastic, piezoelectric and dielectric constants of tetragonal PbTiOs single crystals. Ferroelectrics 141 313-325 MarraSP, Ramesh KT, Douglas AS (1999) The Mechanical properties of lead-titanate/polymer 0-3 composites. Compos Sci Technol 59 2163-2173 Materials Data Sheets of APC International, Tokin, Ferroperm, Morgan Matroc, Siemens Mattiat OE (1971) Ultrasonic transducer materials. Plenum Press, Tokyo McLachlan DS, Blaszkiewicz M, Newnham RE (1990) Electrical resistivity of composites. J Am Ceram Soc 73 2187-2203... 

Acoustic transducers for LMFR plications are usually based on piezoelectric materials. The material used depends on the temperature at which it is to operate, because the piezoelectric properties are lost above the Curie tonperature. At low tonperatures, up to about 2S0°C, lead zirconate titanate ("PZT"), whidi has a Curie point of 3S0X, is acceptable. At higher temperatures lithium niobate, with a Curie point of 1200X, is used. 

The ion valence of donor-type impurity atoms is higher than that of the constituent atoms, and A site vacancies are introduced. In perovskite BaTiOj, donor atoms are known to suppress the peak dielectric and piezoelectric properties. This is believed to be due to a compensating valence change of some of the TL to TL since Ba is not volatile. In lead perovskites, such as lead zirconate titanate (PZT) or lead titanate (PT), it is believed that the excess lead created by the vacancies is allowed to leave the structure because of its high... 

These positive traits come at costs in terms of dielectric and piezoelectric constants when compared with traditional piezoceramics (lead zirconate tilanales and modified lead titanates). However, the low material properties can be partially design compensated for in many applications. 

PZT (lead zirconate titanate) and PLZT (lead lanthanum zirconate titanate) combine ferroelectic, optical, and electronic properties and are used in optoelectronic and piezoelectric devices. Powders for hot pressing produced by CVD are being investigated. 

---