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Crystal structures and thermal properties of some rare earth alkoxides with tertiary alcohols

Possible precursors for atomic layer deposition of rare earth oxides

Journal of Thermal Analysis and Calorimetry
Authors: Timo Hatanpää, Kaupo Kukli, Mikko Ritala and Markku Leskelä

Abstract

Rare earth (RE) alkoxides of Y, La, Pr, and Gd were synthesized using three tertiary alcohols namely 2,3-dimethyl-2-butanol, 2,2-dimethyl-3-ethyl-3-pentanol, and 3-isopropyl-2,4-dimethyl-pentan-3-ol. 1H and 13C NMR, elemental analysis (CHN) and MS were used to characterize the complexes. New crystal structures of dimeric [Y(OCEt2 tBu)3]2, [La(OCEt2 tBu)3]2, [Gd(OCiPr3)3]2, and [La(OCiPr3)3]2 were solved. Thermal properties of these compounds were studied with TG/SDTA and vacuum sublimation experiments. With all the cations Y, La, Pr, and Gd, the compounds with smallest ligand iPrMe2CO seem to be the most volatile. The compounds with larger alkoxo ligands have lower volatility but their thermal stability is better. Atomic layer deposition experiments showed that RE oxide thin films could be grown from these alkoxides using water as the oxygen precursor.

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Journal of Thermal Analysis and Calorimetry
Authors: Imre Miklós Szilágyi, Eero Santala, Mikko Heikkilä, Marianna Kemell, Timur Nikitin, Leonid Khriachtchev, Markku Räsänen, Mikko Ritala and Markku Leskelä

Abstract

This article demonstrates how important it is to find the optimal heating conditions when electrospun organic/inorganic composite fibers are annealed to get ceramic nanofibers in appropriate quality (crystal structure, composition, and morphology) and to avoid their disintegration. Polyvinylpyrrolidone [PVP, (C6H9NO)n] and ammonium metatungstate [AMT, (NH4)6[H2W12O40nH2O] nanofibers were prepared by electrospinning aqueous solutions of PVP and AMT. The as-spun fibers and their annealing were characterized by TG/DTA-MS, XRD, SEM, Raman, and FTIR measurements. The 400–600 nm thick and tens of micrometer long PVP/AMT fibers decomposed thermally in air in four steps, and pure monoclinic WO3 nanofibers formed between 500 and 600 °C. When a too high heating rate and heating temperature (10 °C min−1, 600 °C) were used, the WO3 nanofibers completely disintegrated. At lower heating rate but too high temperature (1 °C min−1, 600 °C), the fibers broke into rods. If the heating rate was adequate, but the annealing temperature was too low (1 °C min−1, 500 °C), the nanofiber morphology was excellent, but the sample was less crystalline. When the optimal heating rate and temperature (1 °C min−1, 550 °C) were applied, WO3 nanofibers with excellent morphology (250 nm thick and tens of micrometer long nanofibers, which consisted of 20–80 nm particles) and crystallinity (monoclinic WO3) were obtained. The FTIR and Raman measurements confirmed that with these heating parameters the organic matter was effectively removed from the nanofibers and monoclinic WO3 was present in a highly crystalline and ordered form.

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