JOURNAL OF SOLID STATE CHEMISTRY 73, 480-487 (1988) Synthesis and Structural Characterization of CaTiOa Doped with 0.05-7.5 Mole% Gadolinium(lll) ELIZABETH M. LARSON, P. GARY ELLER,* JOHN D. PURSON, AND CHARLES F. PACE Isotope and Nuclear Chemistry Division, Los Alamos National Laboratory, MS C346, Los Alamos, New Mexico 87545 MICHAEL P. EASTMAN Department of Chemistry, University of Texas at El Paso, El Paso, Texas 79968 AND R. B. GREEGOR AND F. w. LYTLE Boeing Corporation, Seattle, Washington 98124 Received April 15, 1987; in revised form September 25, 1987 Titanates containing 0.05-7.5 mole% gadolinium(II1) in the CaTiOj perovskite lattice have been pre- pared and characterized by X-ray diffraction and absorption, electron paramagnetic resonance, and Raman methods. The structural studies confirm the predicted site substitution of Gd3+ ions into the Ca2+ sites and suggest charge compensation by a cation deficiency mechanism (Ca*+ and/or Ti4+ vacancies). Evidence is presented for a significant difference between local Gd3+-substituted sites and the average Ca(Gd) sites, resulting from the difference in charge and size of the two ions. A least- squares refinement of single-crystal X-ray data was carried out on (Ca,,.925G&.o,s)Ti0,, with resulting cell parameters and major structural features within three standard deviations of those previously found for stoichiometric CaTi03: space group Pbnm, a = 5.381(l), b = 5.449(l), c = 7647(l) A, Z = 4, R = 4.1% for 236 reflections with Z 2 2u(Z). o 1988 Academic press, I~C. Introduction cific site selectivity being determined by ionic size. Charge balance would be Calcium titanate, CaTi03, is one constit- achieved through appropriate substitution uent of several titanate ceramic composites by coexisting charge-compensating cations. which have been proposed as hosts for However, recent studies on several calcium long-term disposal of high-level nuclear titanates and on related phases have shown wastes (I, 2). Originally, transuranic and that this model is no doubt overly simplis- fission product elements (including lan- tic, particularly at the desired high waste thanides) were expected to enter these loadings (10% or greater) (3-8). A variety phases by random substitution, with spe- of structural techniques have been used to show that complicated cation ordering, * To whom correspondence should be addressed. shear effects, and even twinning on a unit 0022-4596188 $3.00 480 Copyright 0 1988 by Academic Press, Inc. All rights of reproduction in any form reserved.