A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

YTTRIUM OXIDEPlasma spraying of yttria powder onto less stable but more economical materials, e.g graphite, canproduce suitable crucibles, e.g. for containing reactive molten metals.Yttria can be sintered, with the aid of lanthanum oxide or other additives, to produce atransparent material suitable for optical windows that are transparent from 280nm out into theinfrared near 8000nm[6]. In addition yttria is being explored as the envelope material for dischargelamps[7].The sintering of powder precursors to prepare high-temperature structural ceramics benefitsfrom additives to achieve a near-100% ideal density. Such aids work by the transient formation ofan intermediate phase and the solution / precipitation of the dominant material. Yttrium oxide is thepreferred additive for sintering Si 3 N 4 [8], AlN, Si-Al- O-N's[9] and it also used for such species asMgO and SiC.Zirconia can be stabilized against destructive phase transformations by the addition ofanother oxide, e.g. a few mole percent of yttria can create yttria-stabilized-zirconia (YSZ).Variations of such a material are used as plasma-spray coated thermal barrier coatings to preventmetal surfaces from degradation at high temperatures, e.g. on surfaces exposed to jet enginetemperatures. Tough zirconia ceramics are sintered fine-grained tetragonal ZrO 2 polycrystals(TZP's) containing ≈3 mole percent of yttria that can be used as cutting tools and enginecomponents. In addition higher Y 2 O 3 loadings in ZrO 2 with enhanced oxide ion conductivity formthe oxygen sensors used to monitor exhaust gas compositions of vehicles.Microwave communication relies on devices made from yttrium iron garnets YIG's, in whichthe magnetically active iron atoms are locked into the garnet structure Y 3 Fe 5 O I2 . These devices canbe magnetically tuned for frequency selection[10].The crystal structure of Y 2 O 3 readily accepts similarly sized Ln ions such as europium; the dopantscan be chosen to provide visible emission upon excitation by energy sources such as electron orultra-violet radiation. (Yttrium has no emissions because it has no low-lying energy levels.) Thephosphor Eu:Y 2 O 2 S gives the red to almost all television and color CRT's. Other specialized CRTphosphors, for example for projection television, are based on such compounds as yttriumaluminum garnet, YAG, Y 3 Al 5 O 12 .[6] Controlled Transient Solid Second Phase Sintering of Yttria, W.H.Rhodes, J.Am.Ceram.Soc., 198 64(1),13: Lanthana-Doped Yttria, A New Infra-Red Window Material, W.H.Rhodes et al., SPIE Pro 1986, 693, 12[7] Sodium Resistance of Certain Refractory Materials for Use in High Pressure Sodium Vapo DischargeLamps, Y.Tsukuda, J.Canad.Ceram.Soc., 1982, 51, 16[8] High Performance Silicon Nitride Materials, C.Boberski et al., Angew.Chem.Int.Ed.Adv.Mater., 1992,28(11), 1560[9] SiAlON Ceramics, T.Ekström, J.Am.Ceram.Soc., 1992, 75(2), 259[10] YIG Filters, P. Röschmann, Philips Tech.Rev., 1971, 32, 322: Magnetically Tuneable OscillatorsOscillators and Filters, H.Tanbakuchi et al., IEEE Trans.Magn., 1989, 25(5), 324856