Zircon polarization

Some perovskites are widely used as piezo-transducers, BaTi03 for example, and lead zirconate (PbZr03) which is a well-known ferroelectric material sensitive to stresses. Also, some perovskites are good pyro-transducers that is, heat causes electric polarization of them. 

The alcohol exchange reaction was shown above in equation (2). The reactive alkoxy group (OR) is replaced by an alkoxy group that has less hydrolysis sensitivity (OR ). A representative example here is the use of reagents such as zirconium n-propoxide and titanium /-propoxide, both of which possess polar bonds, for the production of lead zirconate titanate films. Commonly in these processes, R OH is 2-methoxyethanol (CH3OCH2CH2OH), which is generally present as a bidentate ligand.35... 

Zircon belongs to the tetragonal system and is a positive uniaxial. The typical form shows the ill and the 110 planes. The two orientations selected for luminescence polarization study were the (110) plane, parallel to the basal section and the [100] row. In such cases the axis perpendicular to the (110) plane will be called X. The orientation notation is made according to the so-called Porto notation (Porto et al. 1956). The Xi(ZX2)Xi orientation means that the laser light entered parallel to the Xi axis of the crystal and is polarized in the Z direction, while the emission is collected along the Xi axis with X2 polarization. By polarization spectroscopy with a high spectral resolution (less then 0.1 nm) six lines are observed for the Dq- Fi transition of the Eu-II center instead of the maximum three allowed for an unique site (Fig. 5.12). In Z(XX)Z geometry which corresponds to observation of a-polarized luminescence we... 

Fig. 5.12. a-c Laser-induced polarized spectra of synthetic zircon artificially activated by Eu... 

Thus at least three Eu " centers take place in zircon, which have been characterized in Table 5.1 by the main transitions, polarizations and decay times of each emitted level. These centers may be reasonably connected with Zr + cation substitution within a tetragonal ZrSi04 structure with space group I4i/amd... 

Electrostrictive materials are materials that exhibit a quadratic relationship between mechanical stress and the square of the electnc polarization. Electrostriction can occur in any material. Whenever an electric field is applied, the induced charges attract each other, thus, causing a compressive force. Tlus attraction is independent of the sign of the electnc field. Typical electrostrictive materials include such compounds as lead manganese niobate, lead titanate (PMN FT), and lead lanthanium zirconate titanate (PLZT). 

Lead lanthanum zirconate titanates (PLZT) containing 3-12 mol. % La and 5-30 mol. % Ti form a class of ceramics with important dielectric, piezoelectric and electro-optic properties. They may contain vacancies on B as well as A sites and have a remarkable facility for changing their polar states under the influence of applied fields. 

Devices based on lanthanum lead zirconate titanate (PLZT) using polarized fight can be switched from transparent to opaque in microseconds. Welding goggles and aircraft windows offer protection from sudden flashes of intense fight. 

Similar relationships are found for other elements like Sc and Cr. In the sand-sized fractions, the REE distribution patterns show a more pronounced negative Eu anomaly and higher La/Lu ratio for the material from Unit N as compared to samples from Unit B. Interpretation of these observations is difficult because the heavy fractions contain as many as 10 different minerals. Pyroxene (mainly augite), amphiboles (mainly hornblende), iron oxides, chromite, ilmenite, rutile, and zircon were identified by using a polarizing microscope and energy-dispersive X-ray analysis. However, the... 

In many cases inclusions in apatite can be detected during the grain selection process. At Caltech apatites to be dated are inspected at 120 x under a binocular microscope using transmitted light and crossed-polarizers. When the apatites are taken to extinction even tiny inclusions of phases like zircon stand out—in some cases entire grains appear to be shot full of inclusions. These grains are easily removed prior to analysis. In rare cases this technique has been found inadequate, usually because the inclusions are oriented parallel to the c-axis (possibly from exsolution of monazite) and are extinct at the same time as the apatite host. In these cases the re-extract test (see the Appendix) and age irreproducibility are sufficient to identify problem samples. 

Grew ES, Kazuhiro S, Masao A (2002) CHIME ages of xenotime, monazite, and zircon from beiylhum pegmatites in the Napier Complex, Khmara Bay, Enderby Land, East Antarctica. Polar Geosci 14 99-118... 

Table 31.2 lists K for a range of materials. Many ceramics and glasses have k in the range of 4-10. Polarization is electronic only in covalent ceramics such as diamond and is a combination of electronic and ionic in materials such as MgO. Some ceramics, in particular BaTiOs and other titanates and zirconates, have very large k due to their permanent dipole moments. 

Shvartsman VV, KhoUdn AL, Orlova A, Kiselev D, Bogomolov AA, Sternberg A (2005) Polar nanodomains and local ferroelectric phenomena in relaxor lead lanthanum zirconate titanate ceramics. Appl Phys Lett 86 202937... 

Ma, W., Cross, L.E. Strain-gradient-induced electric polarization in lead zirconate titanate ceramics. Appl. Phys. Lett. 82, 3293-3295 (2003)... 

Transparent ferroelectric single crystals are traditionally used for electro-optic applications. Since the optical transparency was first discovered in lead-lanthanum-zirconate-titanate (PLZT), ferroelectric ceramics have been investigated in great depth such that, today, their characteristics allow them to compete with single crystals for certain electro-optic applications. The electro-optic properties of PLZT compositions are intimately related to their ferroelectric properties. Variations in ferroelectric polarization with an electric field, such as in a hysteresis loop, also affect the optical properties of the material. 

Until the late sixties the only known ferroelectrics, piezoelectrics, and pyroelectrics were certain inorganic monocrystals, or polycrystalline ceramics like lead titanate zirconate perovskites. Other known materials with macroscopic polarization were electrets, (for example mixmres of beeswax and rosin) in which the polarization was produced by application of the electric field in the melted state and then by cooling and the solidification of the polarized material. 

Actuator materials are classified into three categories piezoelectric, elec-trostrictive and phase-change materials. Modified lead zirconate titanate [PZT, Pb(Zr,Ti)03l ceramics are currently the leading materials for piezoelectric applications. The PLZT [(Pb,La)(Zr,Ti)03l 7/62/38 compound is one such composition [31], The strain curve is shown in Figure 4.1.19a (left). When the applied field is small, the induced strain x is nearly proportional to the field E (x = dE, where d is called the piezoelectric constant). As the field becomes larger (i.e. greater than about IkV/cm), however, the strain curve deviates from this linear trend and significant hysteresis is exhibited due to polarization reorientation. This sometimes limits the use of such materials for actuator applications that require non-hysteretic response. 

In this method, acoustic waves are generated by a piezoelectric transducer, which converts an oscillating electric field to a mechanical oscillation. Detection of acoustic waves that have traveled through a polymer specimen is done with the same type of transducer. Depending on its use, a transducer is called a transmitting transducer (transmitter) or receiving transducer (receiver). Common transducer materials are quartz and various polycrystalline ceramics, such as lead zirconate titanate (PZT), polarized in a strong electrostatic field. 

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