The energetics of lanthanum tantalate materials

被引:31
作者
Forbes, Tori Z. [1 ,2 ]
Nyman, May [3 ]
Rodriguez, Mark A. [3 ]
Navrotsky, Alexandra [1 ,2 ]
机构
[1] Univ Calif Davis, Peter A Rock Thermochem Lab, Davis, CA 95616 USA
[2] Univ Calif Davis, NEAT ORU, Davis, CA 95616 USA
[3] Sandia Natl Labs, Albuquerque, NM 87185 USA
关键词
Rare earth; Lanthanum; Tantalate; Calorimetry; LAYERED PEROVSKITE COMPOUND; RARE-EARTH NIOBATES; TA; ND; LA; LN; CONDUCTIVITY; DIRECTIONS; ENTHALPIES; PROGRESS;
D O I
10.1016/j.jssc.2010.08.024
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Lanthanum tantalates are important refractory materials with application in photocatalysis, solid oxide fuel cells, and phosphors. Soft-chemical synthesis utilizing the Lindqvist ion, [Ta6O19](8-), has yielded a new phase, La2Ta2O7(OH)(2). Using the hydrated phase as a starting material, a new lanthanum orthotantalate polymorph was formed by heating to 850 degrees C, which converts to a previously reported LaTaO4 polymorph at 1200 degrees C. The stabilities of La2Ta2O7(OH)(2) (LaTa-OH), the intermediate LaTaO4 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(2)Ta(2)O(7)(OH)(2) analogues of Ln=Pr, Nd to examine the relationship between cation size and the resulting phases. Published by Elsevier Inc.
引用
收藏
页码:2516 / 2521
页数:6
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