Formation enthalpies of rare earth titanate pyrochlores

• Published in: Journal of solid state chemistry Vol. 177; no. 6; pp. 1858 - 1866
• Main Authors: Helean, K.B., Ushakov, S.V., Brown, C.E., Navrotsky, A., Lian, J., Ewing, R.C., Farmer, J.M., Boatner, L.A.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.06.2004; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; Enthalpy; Exact sciences and technology; Inorganic compounds; Nuclear waste; Physics; Pyrochlore; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Thermodynamics; Water, oxides, hydroxides, peroxides; Pyrochlore; Thermodynamics; Enthalpy; Nuclear waste; Inorganic compounds; Amorphization; Ternary compounds; Transition element compounds; Refinement; Perovskites; XRD; Rare earth compounds; Experimental study; Pyrochlore type compound; Lutetium Titanates; Lanthanum Titanates; Monocrystals; Transmission electron microscopy; Samarium Titanates; Aqueous solutions; Crystal growth from solutions; Sol-gel process; Crystal structure
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2004.01.009

High-temperature oxide melt solution calorimetry and Rietveld refinements of powder X-ray diffraction data were used to investigate the structure ( Fd3m; Z=8) and energetics of a series of RE 2Ti 2O 7 ( RE=Sm–Lu) compounds with the pyrochlore structure as well as La 2Ti 2O 7 with a layered perovskite-type structure. All of the RE-titanates were found to be stable in enthalpy with respect to their oxides. In the pyrochlore series, Lu 2Ti 2O 7 was least stable in enthalpy (Δ Hf-ox at 298 K=−56.0±4.0 kJ/mol); the most stable materials were Gd-, Eu-, and Sm 2Ti 2O 7 with Δ Hf-ox at 298 K=−113.4±2.7, −106.1±4.2, −115.4±4.2 kJ/mol, respectively. In general, as the radius ratio of the A- to B-site cations, R A / R B , decreases, the pyrochlore structure becomes less stable. The trend of ionic radius of the RE 3+ cation vs. Δ Hf-ox at 298 K is non-linear and approximately parallels the increasing “resistance” to ion-beam-induced amorphization as R A / R B decreases.