PZT ceramic

Piezoelectric materials based on the solid solutions of PbZrOs (PZ) and PbTiOs (PT) have been studied already for 50 years (Buchanan 1986 Berhncourt 1981 Cross 1996 Levinson 1988 Nowotny 1992 Newnham and Ruschau 1996 Okazaki 1985). System is known as PZT ceramics. It has excellent piezoelectric properties, which could be designed to meet specific application needs also by doping by different substitution atoms. Because of very reasonable price PZT ceramics is widely used in applications today (Table 7.14). 

Solid solution of PT and PZ exhibit the morphotropic phase boundary (MPB) at 48-52% of mol PT content in the temperature range important for technical 

Property Pz29 N-10 Vibrit 1100 PZT 5H APC856 Pz24 N-8 Vibrit 202 PZT 8 APC 841 

Curie temperature c is very important parameter for the apphcations of fer-roelectrics in general. For PZT ceramics, the phase above Curie temperature is a paraelectric and also non-piezoelectric (isotropic). If the piezoelectric properties are used in applications, material cannot be exposed to the temperatures above Curie temperature to preserve ferroelectric properties. It is recommended by PZT manufacturers not to nse PZT ceramics above 1 /2 c. Curie temperatures for commercially produced PZT s are usually between 150 and 360 C (Materials data sheets of manufacturers). Similarly to the electric field and temperature, the hmits for PZT applicability exist also for the mechanical pre-stress. Typical values for the electric 

Chemical composition (and also material properties) could be modified to meet specific application needs by the addition of atoms of Nb, Sr, Fe, Mn, Cr etc. Special type of PZT ceramics is a La-doped PZT, commonly abbreviated as PLZT. Such ceramics is transparent, which could be controlled by the applied electric field. Chemical composition and manufacturing technology is usually proprietary know-how of each PZT manufacturer and it is not known to the end-users of PZT products. 

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The development of active ceramic-polymer composites was undertaken for underwater hydrophones having hydrostatic piezoelectric coefficients larger than those of the commonly used lead zirconate titanate (PZT) ceramics (60—70). It has been demonstrated that certain composite hydrophone materials are two to three orders of magnitude more sensitive than PZT ceramics while satisfying such other requirements as pressure dependency of sensitivity. The idea of composite ferroelectrics has been extended to other appHcations such as ultrasonic transducers for acoustic imaging, thermistors having both negative and positive temperature coefficients of resistance, and active sound absorbers. 

In lead zh conate, PbZrOs, the larger lead ions are displaced alternately from the cube corner sites to produce an antifeiToelectric. This can readily be converted to a feiToelectric by dre substitution of Ti" + ions for some of the Zr + ions, the maximum value of permittivity occumirg at about the 50 50 mixture of PbZrOs and PbTiOs. The resulting PZT ceramics are used in a number of capacitance and electro-optic applicahons. The major problem in dre preparation of these solid soluhons is the volatility of PbO. This is overcome by... 

The crystallographic and piezoelectric properties of the ceramics depend dramatically on composition. As shown in Fig. 9.4, the zirconate-rich phase is rhombohedral, and the titanate-rich phase is tetragonal. Near the morphotrophic phase boundary, the piezoelectric coefficient reaches its maximum. Various commercial PZT ceramics are made from a solid solution with a zirconate-titanate ratio near this point, plus a few percent of various additives to fine tune the properties for different applications. 

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... 

Table 9.1. Important properties of PZT ceramics commonly used in courtesy of Morgan Matroc Inc., Vernitron Division, Bedford, Ohio. STM. By...

Germano, C. P. (1959). A study of a two-channel cylindrical PZT ceramic transducer for use in stereo phonograph cartridges. IRE Transactions on Radio, July-August 1959, 96-100. 

Comparison of different commercially available Zr02 samples in sintering of PZT ceramics has demonstrated that crystallization of PZT occurs in one step only if samples prepared by hydrolysis of alkoxides are used [1697],... 

Mixer type Ultrasonic micro mixer PZT ceramic width, length, thickness 5 mm, 4 mm, 150 pm... 

The present work summarizes opportunities of using high-resolution synchrotron and standard xrd techniques for structural characterization as well as for investigations of structure-property-relationships. xrd will be used to determine quantitatively the phase content of morphotropic pzt. Temperature dependent measurements provide information about the phase transformation of morphotropic donor doped pzt ceramics and high-resolution synchrotron X-ray diffraction gives information about the extrinsic and intrinsic contributions to the electric field induced strain, xrd results are finally compared with electrical measurements to analyze the interactions among microstructure, phase content and properties. 

Figure 7.1 Typical XRD spectra of a morphotropic pzt ceramic with the corresponding peaks of the tetragonal (Fr) and rhombohedral (Fr) phase.

Figure 7.6 X-ray diffraction patterns for two La-doped PZT ceramics at 40°C and 160°C. (a) PZT (53/47) shows a change in lattice distortion and (b) PZT (54/46) a change in phase composition.

Figure 7.7 Temperature dependence of the relative permittivity for PZT ceramics near the mpb. pzt (54/46) undergoes a partial Fr Ft phase transition between 40 and 80°C.

Our results reveal the opposite effect for compositions next to the mpb which leads us to the conclusion that the monoclinic phase does not play an important role for the performance of doped pzt ceramics. 

Evidence of creep-like piezoelectric response in soft PZT ceramics... 

Figure 13.9 Frequency dependence of the total piezoelectric coefficient in soft PZT ceramics at different amplitudes of the driving field.

PZT it has not been found possible to obtain a PZT ceramic as resistant to high pressures as BaTi03. For this reason the use of cobalt-doped BaTi03 for producing high acoustic powers has continued in some applications, despite its inferior piezoelectric activity. 

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. 

A filter is required to pass a certain selected frequency band, or to stop a given band. The passband for a piezoelectric device is proportional to k2, where k is the appropriate coupling coefficient. The very low k value of about 0.1 for quartz only allows it to pass frequency bands of approximately 1% of the resonant frequency. However, the PZT ceramics, with k values of typically about 0.5, can readily pass bands up to approximately 10% of the resonant frequency. Quartz has a very high Qm (about 106) which results in a sharp cut-off to the passband. This, coupled with its very narrow passband, is the reason why the frequency of quartz oscillators is very well defined. In contrast PZT ceramics have Qm values in the range 102—103 and so are unsuited to applications demanding tightly specified frequency characteristics. 

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