Piezoelectric materials quartz

The measurement of mass using a quartz crystal microbalance is based on the piezoelectric effect.When a piezoelectric material, such as a quartz crystal, experiences a mechanical stress, it generates an electrical potential whose magnitude is proportional to the applied stress. Gonversely, when an alternating electrical field is... 

Since discovering and making use of the piezoelectric effect in naturally occurring crystals such as quartz and Rochelle salts, scientists have produced a wide range of piezoelectric materials in the laboratoi y. An early example is barium titanate, used in an electrical component called a capacitor. Currently, most piezoelectric materials are oxide materials based on lead oxide, zirconate oxide, and titanium. These very hard piezoelectric materials are termed piezoceramics. 

This is the efficiency of energy conversion between mechanical and electrical forms. For PZTs, it ranges from 0.5 to 0.7, which are the most efficient of all known piezoelectric materials (see Table 9.1). For quartz, the coupling constant is about 0.1. 

A piezoelectric crystal is one whose dimensions change in an applied electric field. A sinusoidal voltage applied between two faces of the crystal causes it to oscillate. Quartz is the most common piezoelectric material. 

There are two principal types of materials that can function as piezoelectrics the ceramics and polymers. The piezoelectric materials most widely used are the piezoceramics based on the lead zirconate titanate, PZT, formations, mixed sodium and potassium niobates, lithium niobate, and quartz. The advantages of these piezoceramics are that they have a high piezoelectric activity and they can be fabricated in many different shapes. 

More recently methods have also been developed to measure the adsorbed amount on single surfaces and not onto powders. Adsorption to isolated surfaces can, for instance, be measured with a quartz crystal microbalance (QCM) [383]. The quartz crystal microbalance consists of a thin quartz crystal that is plated with electrodes on the top and bottom (Fig. 9.11). Since quartz is a piezoelectric material, the crystal can be deformed by an external voltage. By applying an AC voltage across the electrodes, the crystal can be excited to oscillate in a transverse shear mode at its resonance frequency. This resonance frequency is highly sensitive to the total oscillating mass. For an adsorption measurement, the surface is mounted on such a quartz crystal microbalance. Upon adsorption, the mass increases, which lowers the resonance frequency. This reduction of the resonance frequency is measured and the mass increase is calculated [384-387],... 

There are several types of materials that exhibit the piezoelectric effect. Because it is inexpensive, and because it has a relatively strong piezoelectric coefficient, quartz is the material of choice for most piezoelectric sensor applications. It has a hexagonal crystallographic structure, with no center of symmetry. Both the magnitude of the piezoelectric coefficient and the extent of its temperature dependence are affected by the orientation of the cut of the crystal with respect to the main crystallographic axes. The most popular AT-cut is shown in Fig. 4.2. 

This scattering mode occurs only in piezoelectric materials, i.e., in crystals without inversion symmetry, and is caused by the electric field associated with acoustical phonons. Zinc oxide exhibits very high electro-mechanical coupling coefficients P (see later), exceeding that of quartz [42,59], which is one of the mostly used piezoelectric materials. Zook [60] has calculated the piezoelectrically limited mobility on the basis of the elastic and piezoelectric constants as (see also Rode [54]) ... 

When it is struck or pressed, quartz generates an electric current. Materials having this property are known as piezoelectric materials. If an external voltage is applied across the crystal, the crystal undergoes vibrations that are in resonance with the alternating current frequency. This type of behavior is the basis for quartz being used as a timing device in watches or in crystals used to establish radio frequencies. 

Quartz, a crystalline form of SiOa, is by far the most commonly used platform for AW sensors, a result of its relatively low temperature coefficient (compared to other piezoelectric materials). Though it is far from trivial to grow,... 

The response of this detector is based on the fact that the frequency output from piezoelectric material is influenced by the weight of the coatings or layers on its surface. This effect has been used for many years to measure trace concentrations of water vapor in a gas and xylene vapor in air has been detected by this means at concentrations as low as lO g/ml. It was first introduced as a GC detecting system by King [22]. The detector consists of a quartz crystal (coated with a high boiling liquid) that is appropriately situated in an electronic circuit that causes it to oscillate at its natural frequency. The oscillation frequency is continuously monitored by a separate circuit. 

In the gravimetric method, the adsorbent (usually in the form of powder) is placed into a bulb, which is mounted on a sensitive balance and the bulb is then evacuated. Next, the weight increase of the adsorbent solid as a function of the absorptive gas pressure is monitored at constant temperature. More recently, the quartz crystal microbalance (QCM) technique has been applied this is very sensitive to mass increases. Quartz is a piezoelectric material and the thin crystal can be excited to oscillate in a traverse shear mode at its resonance frequency when a.c. voltage is applied across the metal (usually gold) electrodes, which are layered on two faces of the crystal. When the mass on the crystal increases upon adsorption, its resonance frequency decreases. The increase in the mass is calculated from the reduction in resonance frequency. On the other hand, adsorption on single flat surfaces can also be measured by ellipsometry, which measures the film thickness of transparent films optically using the difference between light reflection from bare and adsorbed surfaces. 

The main types of SiOj used in indu.siry are high-purity a-quanz, vimeous silica, silica gel. fumed silica and diaiomaceous eanh. The most important application of quartz is as a piezoelectric material (p. 58) it is used in crystal oscillators and filters for frequency control and modulation, and in electromechanical devices such as transducers and pickups tens of millions of such devices are made each year. There is insufficient natural quartz of adequate purity so it must be synthesized by hydrothermal growth of a s crystal using dilute aqueous NaOH and vitreous SiOy at 4(I0°C and... 

The performance of oscillators depends essentially on the stabihty of the acoustic device [7-9] no matter if working as electromechanical resonator or delay line. Because of its extraordinary importance we will concentrate further on resonators, namely quartz crystal resonators. However, the analysis is descriptive also for other piezoelectric materials and partly for delay line elements as well. 

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... 

As the magnitude of an apphed electric field applied to a piezoelectric material is increased, the amphtude of oscillation increases and there is increasing acceleration of analytes adhered to the surface. This in turn results in an increasing force exerted by the surface on the analytes, which ultimately causes rupture of the bonds attaching the analytes to the surface (Fig. 9). Due to its piezoelectric properties the quartz crystal can be used to detect the excitation of vibrations in the substrate produced by bond rupture, which are converted into an electrical signal. The signal indicates not only the pres-... 

A piezoeiectric is a ceramic materiai (typicaiiy a mixture of Pb, Zr, Ti, and 0) that changes size with applied voltage. Quartz is an example of a naturally occurring piezoelectric. Piezoelectric materials are used to control the tip position in scanned probe microscopes because the changes in the piezoelectric dimensions can be controlled with sub-angstrom precision. 

Both silica glass and quartz, SiOa, are composed of Si04 tetrahedra and neither material posses a centre of symmetry. Why is silica glass not a piezoelectric, whereas quartz is [Note answer is not provided at the end of this book.]... 

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