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LiJunChemistryTrueCompositionStructure.pdf

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https://ir.library.oregonstate.edu/concern/articles/9g54xk40g

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  • The discovery of a brilliant-blue color upon the introduction of Mn³⁺ to the trigonal-bipyramidal (TBP) sites in YInO₃ has led to a search for other hosts for Mn³⁺ in TBP coordination. An obvious choice would be YAlO₃. This compound, which has only been prepared through a citrate precursor route, has long been considered isostructural with YAlO₃. However, Mn³⁺ substitutions into YAlO₃ have failed to produce a product with the anticipated color. We find that the hexagonal structure for YAlO₃ with Al in TBP coordination proposed in 1963 cannot be correct based on its unit cell dimensions and bond-valence sums. Our studies indicate instead that all, or nearly all, of the Al in this compound has a coordination number (CN) of 6. Upon heating in air, this compound transforms to YAlO₃, with the perovskite structure liberating CO₂. The compound long assumed to be a hexagonal form of YAlO₃ is actually an oxycarbonate with the ideal composition Y₃Al₃O₈CO₃. The structure of this compound has been characterized by powder neutron and X-ray diffraction data obtained as a function of temperature, magic-angle-spinning ²⁷Al NMR, Fourier transform infrared, and transmission electron microscopy. Refinement of neutron diffraction data indicates a composition of Y₃Al₃O₈CO₃. We find that the hexagonal structures of YGaO₃ and YFeO₃ from the citrate route are also stabilized by small amounts of carbonate. Surprisingly, Y₃Al₃O₈CO₃ forms a complete solid solution with YBO₃ having tetrahedral borate groups. Other unlikely solid solutions were prepared in the YAlO₃−YMnO₃, YAlO₃−YFeO₃, YAlO₃−YBO₃, YBO₃−YMnO₃, YBO₃−YFeO₃, and YBO₃−YGaO₃ systems.
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file details LiJunChemistryTrueCompositionStructure.pdf 2017-07-25 Pubblico Scaricare