Iron niobates

Kassarjian, M. P., Newnham, R. E., and Biggers, J. V., Sequence of reactions during calcining of a lead-iron niobate dielectric ceramic. Am. Ceram. Soc. Bull., 64, 1108 (1985). 

There are a whole range of lead-containing relaxors based on lead zinc niobate (PZN), lead iron niobate (PFN), lead iron tungstate (PFW), and solid solutions with each other and with BaTiOs (BT), PbTi03 (PT), and SrTiOs (ST). Some of the solid-solution phases are PMN-PT, PMN-PT-PZN, PMN-PZN, PFN-PFW, PFN-PMN, and PFW-PT. 

T. C. Reiley et al., A Low Temperature Firing Thick Film Capacitor Material Based on Lead Iron Niobate Tungstate, Matl. Res. Bull., vol. 19, no. 12, pp. 1543-1549,1984. 

Fusion with caustic soda at 500—800°C in an iron cmcible is an effective method for opening pyrochlores and columbites (20). The reaction mixture is flaked and leached with water to yield an insoluble niobate which can be converted to niobic acid in yields >90 wt% by washing with hydrochloric acid. 

Nowadays a large number of functional crystals belongs to the TTB family and presents electro-optic, ferro- piezo- pyroelectric properties (e g. the well-known barium sodium niobate Ba2NaNb50i5 (BNN)). In this work iron and manganese based Kx(lvr%(]Vr )i-xF3 fluorides (0.4solid state reaction and characterised by different diffraction techniques in order to investigate their crystalline stmcture. 

Pyrochlore.—This is a crude calcium niobate which may also contain appreciable quantities of titanium, thorium and cerium, together with smaller quantities of iron, magnesium, the alkali metals, and fluorine. It does not contain chlorine, and it is of interest in that some specimens are remarkably free from tantalum. It occurs in Norway and near Miask in the Ural Mountains. The ore is brown, forms regular octa-... 

Wohlerite is a niobate of calcium, iron, manganese, sodium, etc., associated with considerable quantities of zirconia and silica. It is found in Norway. Other silicates which contain niobium or tantalum are struverite10 and ilmenorutile.11... 

From Figure 1 it is evident that Fe2C>2, FeNbO, and FeTiCL all have relatively positive flat-band potentials, which is presumably a characteristic of the iron. The band gap in the titan-ate appears to be associated with the [TiO ] octahedra that in the niobate appears to match ferric oxide within structural variability. From such a cursory analysis, there would appear to be no effect from the presence of a second photoactive center in these two materials. 

Group (IV) metal phosphates and phosphonates, transition metal oxides (titanates, silicates, niobates, etc.), layered oxides, and double hydroxides (aluminum, magnesium, iron, etc.) are some of the inorganic compounds used as layered host ma-... 

Figure 9. Conventional model of photorefraction in crystals iron impurity forms defect states of variable valence within the forbidden band gap of a lithium niobate crystal. Optical excitation of the divalent state leads to creation of a mobile electron in the conduction band. This is able to move and recombines with a trivalent iron impurity at another location which becomes divalent. The displacement of charge leads to an electric field and the Pockels electro-optic effect leads to local modification of the refractive index.

Within inorganic photorefractive crystals the optical generation of carriers is associated usually with the oxidation of defect and impurity states within the optical band gap of the crystal, such as iron impurity within lithium niobate crystals, as in Figure 9. 

Niobium and tantalum (both rare, 3x 10 %) are extracted (Fig. 243) from a mineral which is a mixed niobate and tantalate of iron and manganese, (Fe,Mn) (Nb,Ta,Og)2. When it contains more niobium than tantalum it is known as columbite, otherwise as tantalite. 

The thiocyanate method (in various modifications) has been used in determinations of molybdenum in plant material [158], natural waters [28,41], cast iron and steel [25,56,159,160], tantalum, niobium, and tungsten [2], vanadium and its compounds [27] corundum and lithium niobate [55], ores and minerals [161,162], uranium concentrates [29,163] lithium fluoride [164], platinum chloride [42], and fertilisers [56]. A review of applications of the thiocyanate method for determining Mo has been given [165]. 

Potassium niobate, together with the analogous tantalate, is soluble, whereas iron and titanium remain in the insoluble residue, along with 3 to 4 per cent of the niobium. 

A complexing agent, Sequestrol CS, is used to retain traces of iron in the solution. It is added immediately before the sodium chloride. The precipitated sodium niobate settles and filters well. The mother liquor is removed by decantation and the niobate washed by resuspending in 5 per cent sodium chloride solution, before being finally filtered. The final conversion is by means of hydrochloric add, followed by water-washing to remove the chloride ion, i.e. 

Gulanyan, E.K., Dorosh, I.R., Iskin, V.D., Mikaelyan, A.L., Maiorchuk, M.A. (1979). Nondestructive readout of holograms in iron-dop>ed lithium niobate crystals. Soviet Journal of Quantum Electronics, Vol. 9, No. 5, pp.647-649 KiUich, H.C. (1987). A new ap>proach to read volume holograms at different wavelengths. 

S. Shastry, G. Srinivasan, M. 1. Bichurin, V. M. Petrov, A. S. Tatarenko, Microwave magnetoelectric effects in single crystal bilayers of yttrium iron garnet and lead magnesium niobate-lead titanate, PAys. Rev. B, 70, 064416, (2004). 

Figure 4.6 The EXAFS spectra of lead iron tungsten niobate with and without added Mn02. From the distances to coordinating atom calculated from this spectra. It was determined that the Mn02 resided at the grain boundaries. 

Following the successful synthesis of tetraisopropoxoaluminates of later 3d transition metals, the chemistry of their niobate, tantalate and zirconate derivatives has also been extensively investigated since 1985 niobate/tantalate, M(01V)g derivatives of Mn(n), ° chromium, iron, " cobalt, nickel,copper,and zirconate, Zr2(OI )9 derivatives of iron, cobalt, nickel and copper (Eqs 3.44 and 3.45) ... 

Ma J, Wu J, Zheng J, Liu L, Zhang D, Xu X, Yang X, Tong Z (2012) Synthesis, characterization and electrochemical behavior of cationic iron porphyrin intercalated into layered niobate. Microporous Mesoporous Mater 151 325-329... 

The incorporation of other oxides into the pores of zeolites and related materials has been studied to a much lesser extent. Some reports have been published concerning the preparation of intrazeolitic copper oxide [112-115], cobalt oxide [116-118], nickel oxide and nickel niobate [119, 120], iron oxide [121-124], manganese oxide [118], phosphorus oxide [125,126], rhenium oxide [127], zirconium oxide [128], tin oxide [129,130] and rhodium vanadate [120, 131] clusters by impregnation methods. 

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