Browsing by Subject "Perovskites"
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Item Open Access Double perovskite structure induced by Co addition to PbTiO3: Insights from DFT and experimental solid-state NMR spectroscopy(American Chemical Society, 2019) Mete, E.; Odabaşı, S.; Mao, H.; Chung, T.; Ellialtıoğlu, Ş.; Reimer, J. A.; Gülseren, Oğuz; Üner, D.The effects of Co addition on the chemical and electronic structure of PbTiO3 were explored both by theory and through experiment. Cobalt was incorporated into PbTiO3 during the sol–gel process with the X-ray diffraction (XRD) data of the resulting compounds confirming a perovskite structure for the pure samples. The XRD lines broadened and showed emerging cubic structure features as the Co incorporation increased. The changes in the XRD pattern were interpreted as double perovskite structure formation. 207Pb NMR measurements revealed a growing isotropic component in the presence of Co. Consistent with the experiments, density functional theory (DFT)-calculated chemical-shift values corroborate isotropic coordination of Pb, suggesting the formation of cubic Pb2CoTiO6 domains in the prepared samples. Hybrid functional first-principles calculations indicate formation of Pb2CoTiO6 with cubic structure and confirm that Co addition can decrease oxygen binding energy significantly. Experimental UV–vis spectroscopy results indicate that upon addition of Co, the band gap is shifted toward visible wavelengths as confirmed by energy band and absorption spectrum calculations. The oxygen binding energies were determined by temperature-programmed reduction (TPR) measurements. Upon addition of Co, TPR lines shifted to lower temperatures and new features appeared in the TPR patterns. This shift was interpreted as weakening of the oxygen–cobalt bond strength. The change in the electronic structure by the alterations of oxygen vacancy formation energy and bond lengths upon Co insertion is determined by DFT calculations.Item Open Access Future outlook(Springer, 2019-01) Erdem, Talha; Demir, Hilmi Volkan; Erdem, Talha; Demir, Hilmi VolkanIn this final Chapter, we present a future perspective for the light source design. We discuss the existing problems and briefly introduce new material systems and device architectures that can overcome the current issues.Item Open Access Precious metal-Free LaMnO3 perovskite catalyst with an optimized nanostructure for aerobic C–H bond activation reactions: alkylarene oxidation and naphthol dimerization(American Chemical Society, 2021-02-03) Şahin, Yeşim; Sika-Nartey, Abel Tetteh; Ercan, Kerem Emre; Koçak, Yusuf; Senol, Sinem; Özensoy, Emrah; Türkmen, Yunus EmreIn this article, we describe the development of a new aerobic C–H oxidation methodology catalyzed by a precious metal-free LaMnO3 perovskite catalyst. Molecular oxygen is used as the sole oxidant in this approach, obviating the need for other expensive and/or environmentally hazardous stoichiometric oxidants. The electronic and structural properties of the LaMnO3 catalysts were systematically optimized, and a reductive pretreatment protocol was proved to be essential for acquiring the observed high catalytic activities. It is demonstrated that this newly developed method was extremely effective for the oxidation of alkylarenes to ketones as well as for the oxidative dimerization of 2-naphthol to 1,1-binaphthyl-2,2-diol (BINOL), a particularly important scaffold for asymmetric catalysis. Detailed spectroscopic and mechanistic studies provided valuable insights into the structural aspects of the active catalyst and the reaction mechanism.