Journal article
The energetics of lanthanum tantalate materials
Journal of solid state chemistry, Vol.183(11), pp.2516-2521
2010
DOI: 10.1016/j.jssc.2010.08.024
Abstract
Lanthanum tantalates are important refractory materials with application in photocatalysis, solid oxide fuel cells, and phosphors. Soft-chemical synthesis utilizing the Lindqvist ion, [Ta 6O 19] 8−, has yielded a new phase, La 2Ta 2O 7(OH) 2. Using the hydrated phase as a starting material, a new lanthanum orthotantalate polymorph was formed by heating to 850 °C, which converts to a previously reported LaTaO 4 polymorph at 1200 °C. The stabilities of La 2Ta 2O 7(OH) 2 (LaTa−OH), the intermediate LaTaO 4 polymorph (LaTa-850), and the high temperature phase (LaTa-1200) were investigated using high-temperature oxide melt solution calorimetry. The enthalpy of formation from the oxides were calculated from the enthalpies of drop solution to be −87.1±9.6, −94.9±8.8, and −93.1±8.7 kJ/mol for LaTa−OH, LaTa-850, and LaTa-1200, respectively. These results indicate that the intermediate phase, LaTa-850, is the most stable. This pattern of energetics may be related to cation–cation repulsion of the tantalate cations. We also investigated possible LnTaO 4 and Ln 2Ta 2O 7(OH) 2 analogues of Ln=Pr, Nd to examine the relationship between cation size and the resulting phases. The energetics of three lanthanum tantalates were investigated by the high-temperature oxide melt solution calorimetry. The enthalpies of formation from the oxides were calculated from the enthalpies of drop solution to be −87.1±9.6, −94.9±8.8, and −93.1±8.7 kJ/mol for La 2Ta 2O 7(OH) 2, LaTaO 4 (850 °C), and LaTaO 4 (1200 °C), respectively. These results indicate that the intermediate phase, LaTaO 4 (850 °C), is the most stable in energy. [Display omitted]
Details
- Title: Subtitle
- The energetics of lanthanum tantalate materials
- Creators
- Tori Z Forbes - Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, CA 95616, USAMay Nyman - Sandia National Laboratory, POB 5800, Albuquerque, NM 87185, USAMark A Rodriguez - Sandia National Laboratory, POB 5800, Albuquerque, NM 87185, USAAlexandra Navrotsky - Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, CA 95616, USA
- Resource Type
- Journal article
- Publication Details
- Journal of solid state chemistry, Vol.183(11), pp.2516-2521
- Publisher
- Elsevier Inc
- DOI
- 10.1016/j.jssc.2010.08.024
- ISSN
- 0022-4596
- eISSN
- 1095-726X
- Language
- English
- Date published
- 2010
- Academic Unit
- Chemistry; Civil and Environmental Engineering
- Record Identifier
- 9983985815102771
Metrics
22 Record Views