Ferroelectric/piezoelectric BaTiO

A wide array of ferroelectric, piezoelectric and pyroelectric materials have titanium, zirconium and zinc metal cations as part of their elemental composition Many electrical materials based on titanium oxide (titanates) and zirconium oxide (zirconates) are known to have structures based on perovskite-type oxide lattices Barium titanate, BaTiOs and a diverse compositional range of PZT materials (lead zirconate titanates, Pb Zr Tij-yOs) and PLZT materials (lead lanthanum zirconate titanates, PbxLai-xZryTii-yOs) are among these perovskite-type electrical materials. 

Barium carbonate also reacts with titania to form barium titanate [12047-27-7] BaTiO, a ferroelectric material with a very high dielectric constant (see Ferroelectrics). Barium titanate is best manufactured as a single-phase composition by a soHd-state sintering technique. The asymmetrical perovskite stmcture of the titanate develops a potential difference when compressed in specific crystallographic directions, and vice versa. This material is most widely used for its strong piezoelectric characteristics in transducers for ultrasonic technical appHcations such as the emulsification of Hquids, mixing of powders and paints, and homogenization of milk, or in sonar devices (see Piezoelectrics Ultrasonics). 

Ceramic capacitors are prepared with their chemical compositions placing them close to a ferroelectric-paraelectric phase boundary, where the dielectric permittivity is anomalously high. These materials are commonly based on BaTiOs which is similar in structure and properties to the piezoelectric ceramics. 

The main uses of piezoceramics are in the generation of charge at high voltages, detection of mechanical vibrations, control of frequency, and generation of acoustic and ultrasonic vibrations. Most, if not all, commercial piezoelectric materials are based on ferroelectric crystals. The first commercially developed piezoelectric material was BaTiO. One of the most widely exploited piezoelectric materials today, however, is based on the Pb(Ti,Zr)03 or PZT solid solution system. 

Barium titanate is ferroelectric and, by implication, also pyroelectric and piezoelectric. The characteristic of a ferroelectric is that it is polarized in the absence of an applied electric field and the direction of polarization can be reversed. Figure 31.10 shows a rectangular hysteresis loop for a singledomain single crystal of BaTiOs. This loop was obtained at room temperature using a 50 Hz supply. 

Titanates are double oxides of the form MeTiOa or Me2Ti04. Barium titanate BaTiOa and its solid solution crystals with other titanates are especially well-known. BaTiOs crystallizes in the perovskite structure. Its technical importance results from its ferroelectric and associated piezoelectric properties, its high dielectric constant at room temperature, and the interesting semiconducting properties which it exhibits when doped [13]. The remarkable temperature dependence of the electrical resistance of such doped material (the temperature coefficient can be metal-like) is used to advantage in control and circuit devices. 

Electro-optic effects in ferroelectric materials can also be dealt with by similar arguments to those used so far. For example, above the Curie temperature (about 120°C), BaTiOs belongs to a cubic system (m3m), and since it has a center of symmetry does not exhibit piezoelectric or first-order electro-optic effects. Accordingly, the electro-optic effect in this paraelectric phase is the Kerr effect. Using the polarization optical constant R in Eq. 7 instead of an electric field, it can also be expressed in terms of polarization as follows ... 

Ferroelectricity was observed in complex structures such as Rochelle salt, but it was prominently observed in crystals having perovskite structures (ABO3). Most of the well-known piezoelectric materials such as BaTiOs and PbTiOs possess the perovskite structure. 

Fig. 5 The ratio of the relevant component of the piezoelectric coefficient d and the respective polarization is plotted vs. the reciprocal of the respective elastic modulus Y (i.e., the relevant component of the elastic compliance). From left to right Literature data for inorganic ferroelectrics squares) barium titanate (BaTiOs), lead zirconate titanate (PZT), and lead zirconate niobate (PZN). Ferroelectric polymers triangles) polyamide-11 (PA-11), poly(vinylidene cyanide-vinyl acetate) (P(VDCN-VAc)), polyurea-5, poly(vinylidene fiuoride (PVDF)), poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), and poly(vinylidene-hexafiuoropropylene) (P(VDF-HFP)). Polymer ferroelectrets circles) cellular polypropylene (cellular-PP) and tubular-channel poly (fluoro-ethylene-propylene) (FEP) (Qiu et al. 2014)...

The ferroelectric effect was discovered in 1920 by Valasek, who obtained hysteresis curves for Rochelle salt analogous to the B-H curves of ferromagnetism [5.5], and studied the electric hysteresis and piezoelectric response of the crystal in some detail [5.6]. For about 15 years thereafter, ferroelectricity was considered as a very specific property of Rochelle salt, until Busch and Scherrer discovered ferroelectricity in KH2PO4 and its sister crystals in 1935. During World War II, the anomalous dielectric properties of BaTiOs were discovered in ceramic specimens independently by Wainer and Solomon in the USA in 1942, by Ogawa in Japan in 1944, and by Wul and Goldman in Russia in 1946. Since then, many ferroelectrics have been discovered and research activity has rapidly increased. In recent decades, active studies have been made on ferroelectric liquid crystals and high polymers, after ferroelectricity had been considered as a characteristic property of solids for more than 50 years. 

SrTlO-i, BaTiO, Pb(Zr7X1)03 RS, RIBS Piezoelectric and ferroelectric devices ... 

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