Tungsten FERROELECTRICS

There is often a wide range of crystalline soHd solubiUty between end-member compositions. Additionally the ferroelectric and antiferroelectric Curie temperatures and consequent properties appear to mutate continuously with fractional cation substitution. Thus the perovskite system has a variety of extremely usehil properties. Other oxygen octahedra stmcture ferroelectrics such as lithium niobate [12031 -63-9] LiNbO, lithium tantalate [12031 -66-2] LiTaO, the tungsten bron2e stmctures, bismuth oxide layer stmctures, pyrochlore stmctures, and order—disorder-type ferroelectrics are well discussed elsewhere (4,12,22,23). 

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]. 

The validity of this approach can be demonstrated by the example of several complex fluoride compounds that exhibit ferroelectric properties, such as compounds that belong to the SrAlF5 family [402, 403]. The crystal structure of the compounds is made up of chains of fluoroaluminate octahedrons that are separated by another type of chains - ramified chains. Other examples are the compounds Sr3Fe2Fi2 and PbsWjOgFio. In this case, the chains of iron- or tungsten-containing octahedrons are separated from one another by isolated complexes with an octahedral configuration [423,424]. 

In the majority of ferroelectric tungsten bronzes the polar axes are parallel to the A-site tunnels. PbNb206 is an exception below the Curie point it undergoes an orthorhombic distortion in the plane perpendicular to the A-site tunnels as indicated in Fig. 6.16. It possesses four possible polar directions and can be poled successfully in ceramic form. 

Dynamic Random Access Memory FeRAM = Ferroelectric Random Access Memory HCP = Hexagonal close packed HREM = High-resolution electron microscopy HTB = Hexagonal tungsten bronze MPTBh = Monophosphate tungsten bronzes with hexagonal tunnels MPTBp =... 

Randall CA, Guo R, Bhalla AS, Cross LE (1991) Microstracture-properly relations in tungsten bronze lead barium niobate, Pbi tBa Nb206. J Mater Res 6 1720-1728 Reaney IM (1995) TEM observations of domains in ferroelectric and nonferroelectric perovskites. Ferroelectrics 172 115-125... 

Three new Tl -containing phases of the quadratic oxygenated tungsten-bronze type have been isolated and characterized by Z-ray powder diffraction. They are Sr2TlNb50i5, BaCaTlNbgOis, and BaSrTlNbsOis, and all are ferroelectric. 

Tungsten Bronze-Type Family Ba2NaNb 0i (BNN) (LB Ni/mhcr 66-o7j. This crystal is ferroelectric below about 580 °C. The crystal structure is modulated below 300 °C. This material is utilized for optical second-harmonic generation and in optical parametric osdllators (Fig. 4.5-38). 

Potassium Substituted SBN Thin Films. For SBN film synthesis, the crystallization of ferroelectric tungsten bronze phase on substrates encounters the problem of the formation of a low temperature phase. In order to prepare tungsten bronze thin films at lower temperatures, the substitution ofK+ forSr + or site is investigated (Sakamoto, 1996, 1997). 

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