Properties of piezoelectric materials

The scanner controlling the tip position and tip scanning is made from piezoelectric materials. The intrinsic physical and mechanical properties of piezoelectric materials, such as nonlinear piezoelectricity, hysteretic piezoelectricity and creep deformation affect the performance of the scanner. Such properties can generate distortion of SPM imaging during scanning. 

Mechanical, Dielectric, and Thermodynamical Properties of Piezoelectric Materials... 

Tichy, J., Erhart, J., Kittinger, E., Privratska, J., 2010. Fundamentals of Piezoelectric Sensorics Mechanical, Dielectric, and Thermodynamical Properties of Piezoelectric Materials. Springer, Heidelberg. 

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). 

The science and technology of piezoelectric materials has long been dominated by the availability of specific materials with particular properties. Piezoelectric polymers are the most recent class of piezoelectrics developed. 

Crystals with one of the ten polar point-group symmetries (Ci, C2, Cs, C2V, C4, C4V, C3, C3v, C(, Cgv) are called polar crystals. They display spontaneous polarization and form a family of ferroelectric materials. The main properties of ferroelectric materials include relatively high dielectric permittivity, ferroelectric-paraelectric phase transition that occurs at a certain temperature called the Curie temperature, piezoelectric effect, pyroelectric effect, nonlinear optic property - the ability to multiply frequencies, ferroelectric hysteresis loop, and electrostrictive, electro-optic and other properties [16, 388],... 

Of the thirty-two crystal classes, twenty-two lack an inversion center and are therefore known as non-centrosymmetric, or acentric. Crystalline and polycrystalline bulk materials that belong to acentric crystal classes can exhibit a variety of technologically important physical properties, including optical activity, pyroelectricity, piezoelectricity, and second-harmonic generation (SHG, or frequency doubling). The relationships between acentric crystal classes and physical properties of bulk materials are summarized in Table 9.1.1. 

Since ferroelectricity was discovered in 1921 it has been obvious to many scientists and engineers that the two stable polarization states +P and P could be used to encode the 1 and 0 of the Boolean algebra that forms the basis of memory and logic circuitry in all modem computers. Yet until very recently this has been unsuccessful. In fact, although ferroelectric materials are used in a wide variety of commercial devices, it has until now always been the case that some other property of the material - especially pyroelectricity or piezoelectricity - is the characteristic actually employed. Ironically, no devices using ferroelectrics have actually required ferroelectricity to work. 

The values of the piezoelectric properties of a material can be derived from the resonance behaviour of suitably shaped specimens subjected to a sinusoidally varying electric field. To a good approximation the behaviour of the piezoelectric... 

This material has excellent mechanical properties and is used extensively as weather resistant coating for aluminium and various outdoor applications. The piezoelectrical properties of the material have been exploited in a range of electronic applications [220]. 

Of central importance for understanding the fundamental properties of ferroelec-trics is dynamics of the crystal lattice, which is closely related to the phenomenon of ferroelectricity [1]. The soft-mode theory of displacive ferroelectrics [65] has established the relationship between the polar optical vibrational modes and the spontaneous polarization. The lowest-frequency transverse optical phonon, called the soft mode, involves the same atomic displacements as those responsible for the appearance of spontaneous polarization, and the soft mode instability at Curie temperature causes the ferroelectric phase transition. The soft-mode behavior is also related to such properties of ferroelectric materials as high dielectric constant, large piezoelectric coefficients, and dielectric nonlinearity, which are extremely important for technological applications. The Lyddane-Sachs-Teller (LST) relation connects the macroscopic dielectric constants of a material with its microscopic properties - optical phonon frequencies ... 

Selected classes of asymmetric crystal structures exhibit the property of piezoelectricity. With the application of a mechanical strain, piezoelectric materials develop an electrical potential difference across them conversely, when a potential difference is applied to these materials, a displacement occurs. The efficiency of the conversion between mechanical energy and electrical energy is described by the electromechanical coupling constant, which practically ranges to values as high as 0.7 a value of 1 would imply complete conversion between mechanical and electrical energy. 

The material properties of piezoelectric layer are shown in Table 1. Since the temperature variation in the piezoelectric layer is not so large, it is assumed that the properties are independent of temperature. 

Any type of acoustic transducer, such as quartz crystal microbalance (QCM) or surface acoustic wave device (SAW), is fundamentally based on the piezoelectric effect. This was first described in 1880 by Jacques and Pierre Curie as a property of crystalline materials that do not have an inversion centre. When such a material is subjected to physical stress, a measurable voltage occurs on the crystal surfaces. Naturally, the opposite effect can also be observed, i.e. applying an electrical charge on a piezoelectric material leads to mechanical distortion, the so-called inverse piezo effect. These phenomena can be used to transfrom an electrical signal to a mechanical one and back, which actually happens in QCM and SAW. Different materials are ap-pHed for device fabrication, such as quartz, Hthium tantalate, lithium titanate... 

Table 27.5 lists applications of some of the most commercially important mixed metal, perovskite-t5q)e oxides, and illustrates that it is the dielectric, ferroelectric, piezoelectric (see Section 13.9) and pyroelectric properties of these materials that are exploited in the electronics industry. 

ZnO is a widely used functional material due to its rniique optical and piezoelectric properties. It has wide band gap ( 3.37eV), good electrical conductivity ( 5 x lO fl cm ), and piezoelectric property. Incorporating the ZnO film onto IPMC electrodes was studied in a view of developing IPMC for optical applications [Kim et al. (2009)]. Namely, piezoelectric properties of ZnO are potentially able to convert mechanical energy into electrical energy, and in conjunction with the optical properties of the material, the IPMCs coated with thin ZnO film can be of interest for opto-electrical applications. 

The crystal structure of a solid can influence the properties of a material, for example, the structure must be noncentric for a material to demonstrate antiferromagnetic, ferromagnetic, ferroelectric, or piezoelectric behavior. Rapid cooling of a sample from high temperature and/or high pressure can quench in a structure that is not stable at room temperature or atmospheric pressure. High-pressure oxide polymorphs, which are more dense, have been studied to model the earth s interior. Furthermore, unique crystal structure characteristics of a material can allow stmcture-property variation, for example, insertion compound formation in layered materials. 

Ultrasound, like sound and infrasound, is made up of pressure waves, i.e. mechanical as opposed to electromagnetic waves. While the latter travel in vacuo, mechanical waves require an elastic medium to propagate.To generate ultrasound, one must do mechanical work on the propagation medium. Two possibilities are exploited magnetostriction and the piezoelectric properties of some materials. 

At this point it should be clear that the direction of particle displacement and velocity of an acoustic wave can be varied by using piezoelectric crystals of different symmetries and by generating acoustic waves at different orientations with respect to the crystallographic axes. Theory allows the prediction of all these parameters if the properties of the material are known. Such calculations, however, can be complex and time-consuming, since numerical methods are required in many cases. Of course, the results of many previous calculations may be found in the literature. 

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