A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

PRASEODYMIUMtransport of Pr happens through the intermediacy of a transient PrMX n complex. The cause of thecoloration has been attributed solely to the Pr 4+ ion stabilized in the host ZrSiO 4 but it is alsopossible that charge transfer bands contribute. The color of potential red pigments such asCe l-x Pr x O 2 [5] is certainly due to charge transfer bands associated with the Ce(IV)/Pr(IIII)system.[6]A possible Pr(III)/Pr(IV) redox in a fluorite-related structure, with mobile oxide ions,indicates a potential for Pr in catalysis similar to that found for cerium in CeO 2 . As examples, theoxidative coupling of methane over doped Pr 6 O 11 shows a high selectivity to C 2 products[7] andthe oxide Pr 4 PdO 7 catalyzes the oxidation of natural gas fuels as well as having an excellentthermal stability and regenerative behavior[8].On excitation the Pr 3+ ion shows a variety of emissions depending strongly on the host latticedue to the strong influence of that lattice on the energy of the excited 4f5d level.[9] Pr-dopedfluoride fibers have been proposed for optical amplification at 1310 nm for telecommunications; asystem that could rival Erbium-doped fiber amplifiers. Another application of Pr-emission is in thescintillator Pr,Ce,F : Gd 2 O 2 S for X-ray computed tomography[10]. Such scintillators need to bemade as small translucent ceramics with an emitter with a very fast decay time, 5 µs for Pr 3+ , and awavelength matching the detector's sensitivity.Permanent magnets based Praseodymium, a lanthanide more abundant than Samarium, havethe potential to be comparable in properties to the well recognized samarium-cobalt material,SmCo 5 . Certain oxides, added as powders (up to 1 wt %) prior to sintering, can suppress theformation of undesirable impurity phases. The added oxide reacts with any excess Ln in the startingalloy composition and keeps the overall Pr : Co ratio down to the desired 1 : 5. One esoteric use ofthis element is in the intermetallic PrNi 5 that has made possible the attainment of ultra-lowtemperatures, in the micro-Kelvin range[11]. The l4l Pr nuclei have the requisite novel magneticproperties.[5] Optical Properties of Ce l-xPr xO 2 Powders and their Applications to the Coloring of Ceramics, R.Olazcuagaet al., J.Solid State Chem., 1987, 71, 570[6] Charge-Transfer Spectra of Tetravalent Lanthanide Ions in Oxides, H.E.Hoefdraad, J.Inorg.Nucl.Chem.,1975, 37, 1917[7] Methane Conversion, AM.Gaffney (Arco), U.S.Patent, 4,499,323, 12 Feb. 1985[8] Praseodymium-Palladiurn Binary Oxide, Catalyst Compositions containing the Same, and Methods of Use,T.C.Chou et al.(Engelhard), U.S.Patent 5,102,639, 7 April 1992.[9] Chemistry and Physics of R-Activated Phosphors, G.Blasse, in "Handbook on the Physics and Chemistry ofRare Earths", ed. K.A.Gschneidner and L.Eyring, publ. North-Holland, 1979, Vol.4, p.237[10] A Scintillator Gd 2O 2S : Pr, Ce, F for X-Ray Computed Tomography, H. Yamada et al.,J.Electrochem.Soc., 1989, 136(9), 271331