A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

TITANATES, TITANIUM DIOXIDELanthanide titanates can display unusual electrical properties[4] and, mainly in ternarysystems, are used in various electronic ceramic compositions. Barium Lanthanide Titanates,especially those containing Neodymium, are the basis of the dielectric formulations increasinglyused in multi-layer capacitors.[5] These materials have high dielectric constants, low loss factorsand temperature-independent dielectric constants. Within the BaO-TiO 2 -Ln 2 O 3 systems (Ln = La,Nd, and Sm) 1:3:1 and l:(≈4 - ≈5):l compounds have been identified and it is probable that thesespecies account for the desirable dielectric properties.Doping of the common titanate, BaTiO 3 , by other ions is used to create and control physicalproperties. Introduction of a small fraction,≈1 %, of trivalent La, into this titanate can cause theresistivity to increase by several orders of magnitude near the titanate's Curie temperature,≈100°C.[6] These materials are used as thermistors for the protection of electrical equipment.The high refractive index of titanium dioxide makes it a superb white pigment. However it isphotosensitive and u.v. radiation will cause degradation. Lightfastness can be improved by coatingthe surface with a cerium derivative that strongly absorbs the ultra-violet.[7][4] A new Ferroelectric:La 2Ti 2O 7,S.Nanamatsu et al., Ferroelectrics, 1974,8,511:La 2Ti 2O 7 Ceramics, P.A.Fuierer and R.E.Newnham, J.Am.Ceram.Soc., 1991, 74(11), 2876[5] Defect Structure and Dielectric Properties of Nd 2O 3-Modified BaTiO 3, A.Shaikh and R.W.Vest,J.Amer.Ceram.Soc., 1986, 69(9), 689 : Microwave Dielectric Properties of (Ba,Sr)O-Sm 2O 3-TiO 2 Ceramics, S.Nishigaki et al., Am.Ceram.Soc.Bull., 1987, 66(9), 1405 : Synthesis and Characterization of BariumLanthanum Titanates, J.P.Guha, J.Am.Ceram.Soc., 1991, 74(4), 878[6] The PTC Effect of Barium Titanate, J.Daniels et al., Philips Tech.Rev., 1978/79, 38(3), 73[7] Titanium Dioxide Pigment coated with Cerium Cations, selected Acid Anions and Alumina, H.W.Jacobson,U.S. Patent, 4,737,194, 12 April 198849