Electrical properties ferroelectricity

Alkaline-Earth Titanates. Some physical properties of representative alkaline-earth titanates ate Hsted in Table 15. The most important apphcations of these titanates are in the manufacture of electronic components (109). The most important member of the class is barium titanate, BaTi03, which owes its significance to its exceptionally high dielectric constant and its piezoelectric and ferroelectric properties. Further, because barium titanate easily forms solid solutions with strontium titanate, lead titanate, zirconium oxide, and tin oxide, the electrical properties can be modified within wide limits. Barium titanate may be made by, eg, cocalcination of barium carbonate and titanium dioxide at ca 1200°C. With the exception of Ba2Ti04, barium orthotitanate, titanates do not contain discrete TiO ions but ate mixed oxides. Ba2Ti04 has the P-K SO stmcture in which distorted tetrahedral TiO ions occur. 

In this book those ferroelectric solids that respond to shock compression in a purely piezoelectric mode such as lithium niobate and PVDF are considered piezoelectrics. As was the case for piezoelectrics, the pioneering work in this area was carried out by Neilson [57A01]. Unlike piezoelectrics, our knowledge of the response of ferroelectric solids to shock compression is in sharp contrast to that of piezoelectric solids. The electrical properties of several piezoelectric crystals are known in quantitative detail within the elastic range and semiquantitatively in the high stress range. The electrical responses of ferroelectrics are poorly characterized under shock compression and it is difficult to determine properties as such. It is not certain that the relative contributions of dominant physical phenomena have been correctly identified, and detailed, quantitative materials descriptions are not available. 

Merklein, S. Sporn, D. Schonecker, A. 1992. Crystallization behavior and electrical properties of wet-chemically deposited lead zirconate titanate. In Ferroelectric Thin Films III, edited by Tuttle, B. A. Myers, E. R. Desu, S. B. Larsen, P. K. Mat. Res. Soc. Symp. Proc. 310 263-268. 

Haider, S. Schneller, T. Waser, R. Thomas, F. 2007. Microstructure and electrical properties of BaTi03 and (Ba,Sr)Ti03 ferroelectric thin films on nickel electrodes. /. Sol-Gel Sci. Tech. 42 203-207. 

One example has been described of CD (PbS) on a poled ferroelectric substrate. The PbS crystal size was larger (ca. 1 jim) on the poled substrate than on the unpoled (or a glass) substrate (ca. 0.3 jim) [34], Other changes in the electrical properties of the films were noted. The differences were ascribed to the electric field and charge accumulation at the ferroelectric surface (more details can be found in Sec. 5.2.4.3). 

The unique dielectric properties and polymorphism of PVDF are the source of its high piezoelectric and pyroelectric activity.75 The relationship between ferroelectric behavior, which includes piezoelectric and pyroelectric phenomena and other electrical properties of the polymorphs of polyvinylidene fluoride, is discussed in Reference 76. 

Also surface optical properties of a material sometimes need to be changed, for example in making anti-reflection coating for lenses or reflective surfaces for CDs, the magnetic properties may need to be influenced as in the case of giving a ferroelectric surface to a plastic for magnetic recording, and, perhaps most extensively of all, the surface electrical properties need to be controlled in microelectronic devices used in computers and all modern electronic equipment. 

Some keywords for further reading on measurements of electrical properties using the SFM are pulsed-force mode [33, 404, 405], special SFM tips [406-409], lithography assisted by electric potentials [244, 254, 410-426], measurements of polarisation and water droplet manipulation [427-429] or reading and writing of ferroelectric domains and piezoactivity [393, 430-438]. 

Electrical properties of glass ceramics are determined by the properties of both the crystalline phases and the residual glass. Electrical conductivity and dielectric loss (at low frequencies) are dominated by the concentration and mobility of alkali ions in the glass phase. The dielectric constant is dominated by the crystalline phase, especially when that phase consists of high dielectric constant materials such as ferroelectric crystals. The... 

In the present review article 1985 s results obtained in applications of the concept of vibronic interactions to the investigation of electric properties of molecules (dipole and multipole moments and polarizabilities) are presented. Molecular aspects of these topics are almost untouched in the publications listed in the preceding paragraph. The idea of dipole instability was used first as a basis of the so-called vibronic theory of ferroelectricity (Bersuker, 1966 Bersuker and Vekhter, 1978). Meanwhile, the manifestation of the electronic or vibronic degeneracy in the electric responses of molecules, being no less essential than other vibronic effects, has some special features. 

Exists in five cryst modifications. The tetragonal form (obtained by the wet process) appears to have the most desirable electric properties and is described here d 6.08. mp 1625. Curie point 120". Has ferroelectric and piezoelectric properties. Becomes parmanently polarized when exposed to high voltage direct current, provided the temperature is never allowed to rise above Curie pt. Has high dielectric properties which can be influenced by temp, voltage, and frequency. 

H. Beltran, B. Gomez, N. Maso, E. Cordoncillo, P. Escribano and A. R. West, Electrical properties of ferroelectric BaTi205 and dielectric Ba6Tii7O40 ceramics, J. Appl. Phys., 97 084104-1-6 (2005). 

C.-C. Wang, J.-F. Song, H.-M. Bao, Q.-D. Shen, and C.-Z. Yang, Enhancement of electrical properties of ferroelectric polymers by polyaniline nanofibers with controllable conductivities, Adv. Funct. Mater., 18, 1299-1306 (2008). 

Conduction and dielectric properties are not the only electrical properties that polymers can exhibit. Some polymers, in common with certain other types of materials, can exhibit ferroelectric properties, i.e. they can acquire a permanent electric dipole, or photoconductive properties, i.e. exposure to light can cause them to become conductors. Ferroelectric materials also have piezoelectric properties, i.e. there is an interaction between their states of stress or strain and the electric field across them. All of these properties have potential applications but they are not considered further in this book. 

Electrostatic Force Microscopy (EFM) allows to obtain information on the surface electrical properties of materials by measuring electric forces between a charged tip and the surface. It is particularly suitable for the study and manipulation of ferroelectric thin films with large surface charge. Interestingly, an EFM can also be used to study the surface properties of dielectric materials, that are polarized by the electric field of the tip. In this mode of operation, the EFM is sometimes called Polarization Force Microscope and can be used to study and image even air-liquid interfaces [64]. 

We have shown how Electrostatic Force Microscopy can be an extremely useful tool to investigate and to modify the electric properties of sample surfaces on a microscopic and even nanoscopic scale and we have presented a phenomenological model to help relating the experimental data to the material properties. Ferroelectric domains can locally be reoriented and their time evolution can be followed, as was shown for PZT. We have also demonstrated how the ferroelectric polymer PVDF-TrFe could be locally modified which can be used to locally vary the optical properties of a LC cell. Finally, we have demonstrated that rubbing polymer substrates can indeed result in electrostatic charging, in particular for PMMA and PI, while no charging is found for PVA. 

THERMAL AND ELECTRICAL PROPERTIES OF FERROELECTRIC TRIGLYCINE SELENATE NEAR THE CURIE POINT. 

Ferroelectricity in perovskites provides a good example of how the crystal structure of a solid affects its electrical properties and uses. " ... 

FIGURE 12.50 Influence of H-bonding on electrical properties, (a) Ferroelectric KH2PO4, (b) antiferroelec-tric NH4H2PO4. Orthorhombic cells viewed down [c] axes. H bonds parallel to plane of paper. Numerals give heights of P atoms above c = ( ), cations yc above each PO4 tetrahedron. 

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