کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1331063 | 978992 | 2010 | 6 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: The energetics of lanthanum tantalate materials The energetics of lanthanum tantalate materials](/preview/png/1331063.png)
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 °C, which converts to a previously reported LaTaO4 polymorph at 1200 °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 LnTaO4 and Ln2Ta2O7(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 La2Ta2O7(OH)2, LaTaO4 (850 °C), and LaTaO4 (1200 °C), respectively. These results indicate that the intermediate phase, LaTaO4 (850 °C), is the most stable in energy.Figure optionsDownload as PowerPoint slide
Journal: Journal of Solid State Chemistry - Volume 183, Issue 11, November 2010, Pages 2516–2521