Oxides ferroelectric

The second group is the group of oxyfluorides that are derived from ferroelectric oxides by means of fluorine-oxygen substitution. The basic oxides are usually perovskite, tetragonal tungsten bronze, pyrochlore, lithium tantalate etc. [400]. 

It is easy to determine the environment of Pb in PbZrOs accurately, since PbZrOs is a well ordered compound. But many useful ferroelectric oxides, for instance well-known ferroelectric oxides, Pb(Zr,Ti)03 (PZT), are mixed ion systems in which the crystal sites are occupied by two or more different ions. In such systems it is more difficult to assess the state of Pb off-centering with accuracy using conventional crystallographic analysis, such as the Rietveld refinement. Local Pb displacements are often non-collinear, displaced in different directions from site to site. These local displacements will be observed indirectly only as artificially large thermal factors, and the average displace-... 

Reactive Sputtering. Reactive sputtering is similar to reactive evaporation and reactive-ion plating in that at least one coating species enters the system in the gas phase. Examples include sputtering Al in 02 to form A O Ti in 02 to form Ti02, In—Sn in 02 to form tin-doped ln203, Nb in N2 to form NbN, Cd in H2S to form CdS, In in PH3 to form InP, and Pb—Nb—Zr—Fe—Bi—La in 02 to form a ferroelectric oxide. 

Barium titanate, BaTi03, is probably the most widely studied ferroelectric oxide. Extensive studies were conducted on this compound during World War II in the United States, England, Russia, and Japan, but the results were not revealed until after the war. Barium titanium(IV) oxide was found to be a ferroelectric up to a temperature of 120°C., which is its Curie point. Above 120°C., barium titanium(IV) oxide has the cubic perovskite structure, and below this temperature the oxygen and titanium ions are shifted and result in a tetragonal structure with the c axis approximately 1% longer than the a axis. Below 0°C., the symmetry of barium titanate becomes orthorhombic, and below —90°C., it becomes trigonal. 

A general review of photorefractive materials was presented in 1988. 150) Also, two monographs in were published which detail theory, physical characterization and practice of the use of known photorefractives.(151) Three classes of inorganic materials dominate. Ferroelectric oxides, such as LiNbC>3 and BaTiC>3 mentioned above compound semiconductors such as GaAs and InP, and the sillenite family of oxides, exemplified by Bii2SiC>20 and Bii2TiC>20 The semiconductors are sensitive only in the infrared, while the other materials operate in the... 

The most widely known case of phonon-induced charge transfer may be that in ferroelectric oxides, such as BaTi03. In the classic picture of ferroelectricity polarization is produced by positive and negative ions displaced in opposite directions. The polarization is given by uZ, where u is the atomic displacement and Z is the ionic charge. In reality, however, the actual polarization is much larger because of charge transfer ... 

Some of the well-known ferroelectric materials are perovskite oxides. No ferroelectric oxide of K2NiF4 structure has been reported until now similarly, other ferroic properties 87) are yet to be explored. 

The inverse-micelle approach may also offer a generalized scheme for the preparation of monodisperse metal-oxide nanoparticles. The reported materials are ferroelectric oxides and, thus, stray from our emphasis on optically active semiconductor NQDs. Nevertheless, the method demonstrates an intriguing and useful approach the combination of sol-gel techniques with inverse-micelle nanoparticle synthesis (with OTO erafe-temperature nucleation and growth). Monodisperse barium titanate, BaTiOs, nanocrystals, with diameters controlled in the range from 6-12nm, were prepared. In addition, proof-of-principle preparations were successfully conducted for Ti02 and PbTiOs. Single-source alkoxide precmsors are used to ensure proper stoichiometry in the preparation of complex oxides (e.g. bimetallic oxides) and are commercially available for a variety of systems. The... 

Since the early suggestion that ferroelectric thin film materials could be the high dielectric layer in the capacitor of the ultra large scale integrated dynamic random access memory devices (ULSI DRAMS) made by Parker and Tasch, there has been a great deal of research effort to deposit multi-component ferroelectric oxide thin films as well as more recent industrial activity. The term ferroelectric indicates the property of certain materials that have remnant... 

Mixed metal oxides can be addressed as belonging to three main fields, namely superconducting metal oxides (SMOs) (Section V.D.l), transparent conductive oxides (TCOs) (Section V.D.2) and ferroelectric oxides (Section V.D.3). The synthesis procedures for mixed metal oxides include sintering, sol-gel, PLD or laser ablation, sputtering evaporation, MBE, MOVPE (metal-organic vapor-phase epitaxy), OMVPE (organometallic vapor-phase epitaxy) and CVD in particular. 

Ferroelectric oxide Precursors Deposition method Reference... 

One of the remarkable demonstrations of the capabilities of ultraviolet Raman spectroscopy to probe extremely thin ferroelectric oxide layers reported so far has been its application for studies of ultrathin BaTi03 films [48]. In order to investigate the size effect on the ferroelectric phase transitions, variable temperature UV Raman spectroscopy was applied to studies of a series of BaTi03 films with layer thicknesses varied from 1.6 to 10 nm (4—25 unit cells). 

Dawber M, Rabe KM, Scott JE (2005) Physics of thin-film ferroelectric oxides. Rev Mod Phys 77 1083... 

Rudiger A, Schneller T, Roelofs A, Tiedke S, Schmitz T, Waser R (2005) Nanosize ferroelectric oxides - tracking down the superparaelectric limit. Appl Phys A 80 1247... 

Warusawithana MP, Cen C, Sleasman CR, Woicik JC, Li YL, Fitting Kourkoutis L, King JA, Li H, Ryan P, Wang L-P, Bedzyk M, Muller DA, Chen L-Q, Levy J, Schlom DG (2009) A ferroelectric oxide made directly on silicon. Science 324 367... 

Dawber M, Stucki N, Lichtensteiger C, Gariglio S, Triscone J-M (2008) New phenomena at the interfaces of very thin ferroelectric oxides. J Phys Condens Matter 20 264015... 

Wessels, B.W. Metalorganic chemical vapor deposition of ferroelectric oxide thin films for electronic and optical applications. Ann. Rev. Mater. Sci. 1995, 25, 525-546. 

Also of significant interest are ferroelectric oxides. Ferroelectrics such as PbZrTiO (PZT) are useful in permanent memories. Ferroelectrics also are under development in capacitor and display applications. Ferroelectrics surpass SMO thin film applications for the immediate future. In fact, ferroelectrics are being produced in the 150 mm diameter range. 

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