cm9020645_si_001.cif (752.73 kB)

Unique LaTaO4 Polymorph for Multiple Energy Applications

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posted on 13.10.2009, 00:00 by May Nyman, Mark A. Rodriguez, Lauren E.S. Rohwer, James E. Martin, Mollie Waller, Frank E. Osterloh
Rare-earth niobate and tantalate (RE-Nb/Ta) materials are of considerable interest in environmental and energy-related applications that include phosphors for solid-state lighting, photocatalysts for both contaminant degeneration and H2 generation, chemically robust hosts for nuclear materials and wastes, and ion conductors for lithium batteries or solid-oxide fuel cells. However, the chemically inert nature limits the synthetic routes available to obtain these materials, which in turn hampers the discovery and development of new RE-Nb/Ta phases. Of the simple orthotantalate, LaTaO4, there were three polymorphs known prior. With this paper, we present the structural characterization (from high-resolution X-ray powder diffraction data collected at the APS 11-BM line) of a fourth polymorph. It is obtained only from dehydration of La2Ta2O7(OH)2, which is in turn synthesized hydrothermally. The structure of the new LaTaO4 polymorph is distinctive from the others in the arrangement of the alternating La−O polyhedra layers and TaO6 octahedra layers. Luminescence measurements (Eu-doped) and photocatalysis studies of the new LaTaO4 polymorph, and comparison to the performance of a previously described LaTaO4 polymorph reveals enhanced performance of the new polymorph in both applications. This study illustrates the relevance of form-function relationships in solid-state materials, as well as the important role of synthesis in the development of advanced functional materials.