Local structure analysis of solid state ionic conductors, perovskite-derived structures by NMR and computational studies

The full text of this thesis is embargoed until end November 2015 for publication reasons. Supporting data is held on a separate record at https://www.repository.cam.ac.uk/handle/1810/244979In this work, local environments of ions in solid oxide fuel cell (SOFC) electrolyte materials with perovskite and perovskite-derived crystallographic structures, i.e. $Ba_{2}In_{2}O_{5}$, $Ba_{2}(In_{1-x}Ga_{x})_{2}O_{5}$ and $Ba_{2}In_{2}O_{4}(OH)_{2}$, were investigated for their high ionic (O2– and H+) mobility at elevated temperatures. Two general methods were employed in this investigation; first, computational methods, such as density functional theory (DFT), gauge including projector augmented wave (GIPAW), cluster expansion (CE) and Monte Carlo simulations (MC); second, experimental methods, such as nuclear magnetic resonance (NMR), X-ray scattering (both powder diffraction and pair distribution function (PDF) analysis) and thermo-gravimetric analysis (TGA). The parent material, $Ba_{2}In_{2}O_{5}$, has inherent oxygen vacancies which allow for fast O2– ion mobility at elevated temperatures and for hydration of the material needless of doping. We improve a previous NMR study of $Ba_{2}In_{2}O_{5}$ by Adler et al. [1], assigning all three oxygen crystallographic sites to their relevant NMR peaks and investigate the high temperature structure. We then study the iso-valent doping of Ga into the In site resulting in Ba2(In1-xGax)2O5. While Yao et al. [2] find that Ga doping levels higher than 20% form a stable cubic structure, our findings indicate that Ga doping results in a phase segregation. However our findings for quenched samples are no different than those of Yao et al. [2]. Lastly we study the hydrated form of the parent material, $Ba_{2}In_{2}O_{4}(OH)_{2}$, which has high H+ ion mobility above 180C. We observe at least three possible hydrogen sites with local environments slightly different from the previous neutron diffraction study by Jayaraman et al. [3]. In contrast to the observation by Jayaraman et al. [3] of the hydrogen presence in all O2 layers we find an alternating occupancy of hydrogens in those layers

Joint Experimental and Computational O-17 and H-1 Solid State NMR Study of Ba2In2O4(OH)(2) Structure and Dynamics

This is the final version of the article. It first appeared from ACS Publications via http://dx.doi.org/10.1021/acs.chemmater.5b00328A structural characterization of the hydrated form of the brownmillerite-type phase Ba2In2O5, Ba2In2O4(OH)2, is reported using experimental multinuclear NMR spectroscopy and density functional theory (DFT) energy and GIPAW NMR calculations. When the oxygen ions from H2O fill the inherent O vacancies of the brownmillerite structure, one of the water protons remains in the same layer (O3) while the second proton is located in the neighboring layer (O2) in sites with partial occupancies, as previously demonstrated by Jayaraman et al. ( Solid State Ionics 2004, 170, 25?32) using X-ray and neutron studies. Calculations of possible proton arrangements within the partially occupied layer of Ba2In2O4(OH)2 yield a set of low energy structures; GIPAW NMR calculations on these configurations yield 1H and 17O chemical shifts and peak intensity ratios, which are then used to help assign the experimental MAS NMR spectra. Three distinct 1H resonances in a 2:1:1 ratio are obtained experimentally, the most intense resonance being assigned to the proton in the O3 layer. The two weaker signals are due to O2 layer protons, one set hydrogen bonding to the O3 layer and the other hydrogen bonding alternately toward the O3 and O1 layers. 1H magnetization exchange experiments reveal that all three resonances originate from protons in the same crystallographic phase, the protons exchanging with each other above approximately 150 ?C. Three distinct types of oxygen atoms are evident from the DFT GIPAW calculations bare oxygens (O), oxygens directly bonded to a proton (H-donor O), and oxygen ions that are hydrogen bonded to a proton (H-acceptor O). The 17O calculated shifts and quadrupolar parameters are used to assign the experimental spectra, the assignments being confirmed by 1H?17O double resonance experiments.This work was supported in part by Grants DMR050612 and CHE0714183 from the National Science Foundation and Grant DESC0001284 from the Department of Energy (supporting Y.- L.L. and D.M.), by an Advanced Fellowship from the EU-ERC (C.P.G.), and by the EPSRC (D.S.M.). F.B. thanks the EU Marie Curie actions FP7 for an International Incoming fellowship (Grant No. 275212) and Clare Hall, University of Cambridge, for a Research Fellowship

Proton distribution in Sc-doped BaZrO3: a solid state NMR and first principle calculations analysis

Perovskite-based material Sc-doped BaZrO3 is a promising protonic conductor but with substantially lower conductivities than its Y-doped counterpart. H-1 solid-state NMR spectroscopy in combination with DFT modelling was used to analyze the protonic distribution in BaZr1-xScxO3-x/(2-y)(OH)(2y) and its effect on charge carrier mobility. 1H single pulse and H-1-Sc-45 TRAPDOR MAS NMR experiments highlighted the mobile character of the proton charge carriers at room temperature, giving rise to a single broad resonance, protons hopping between multiple sites on the NMR timescale. At low temperatures, the protonic motion was successfully slowed down allowing direct observation of the various proton environments present in the structure. For x <= 0.15, DFT modelling suggested a tendency for strong dopant-proton association leading to Sc-OH-Zr environments with H-1 NMR shifts of 4.8 ppm. The Zr-OH-Zr environment, H-bonded to a Sc-O-Zr, lies 32 kJ mol(-1) higher in energy than the Sc-OH-Zr environment, suggesting that the Sc-OH-Zr environment is trapped. However, even at these low concentrations, Sc-Sc clustering could not be ruled out as additional proton environments with stronger H-1-Sc-45 dipolar couplings were observed (at 4.2 and 2.8 ppm). For x = 0.25, DFT modelling on the dry material predicted that Sc-&-Sc environments were extremely stable, again highlighting the likelihood of dopant clustering. A large number of possible configurations exists in the hydrated material, giving rise to a large distribution in H-1 chemical shifts and multiple conduction pathways. The H-1 shift was found to be strongly related to the length of the O-H bond and, in turn, to the hydrogen bonding and O center dot center dot center dot OH distances. The breadth of the NMR signal observed at low temperature for x = 0.30 indicated a large range of different OH environments, those with lower shifts being generally closer to more than one Sc dopant. Lower DFT energy structures were generally associated with weaker H-bonding environments. Both the calculations and the DFT modelling indicated that the protons tend to strongly bond to the Sc clusters, which, in conjunction with the higher energies of configurations containing Zr-OH-Zr groups, could help explain the lower conductivities recorded for the Sc-substituted BaZrO3 in comparison to its yttrium counterpart

Dataset for PhD thesis "Local Structure Analysis of Solid State Ionic Conductors, Perovskite-derived Structures by NMR and Computational Studies" by Riza Dervisoglu

Appendix A: Computational, output dataA.1 DFT geometry optimized structures, as crystallographic information files (CIF)A.2 GIPAW calculated NMR parameters, as .MAGRES filesThis record contains the supporting data for the thesis "Local Structure Analysis of Solid State Ionic Conductors, Perovskite-derived Structures by NMR and Computational Studies" by Riza Dervisoglu at https://www.repository.cam.ac.uk/handle/1810/24507

Covalently Functionalized Egyptian Blue Nanosheets for Near-Infrared Bioimaging

Fluorophores emitting in the near-infrared (NIR) wavelength region present optimal characteristics for photonics and especially bioimaging. Unfortunately, only few NIR fluorescent materials are known and even fewer are biocompatible. For this reason, the scientific interest in designing novel NIR fluorophores is very high. Egyptian Blue (CaCuSi4O10, EB) is a NIR fluorescent layered silicate that can be exfoliated into fluorescent nanosheets (EB-NS). So far, its surface chemistry has not been tailored but this is crucial for colloidal stability and biological targeting. Here, we demonstrate covalent surface functionalization of EB nanosheets (EBfunc) via Si-H activation using hydrosilanes with variable functionalities. EB-NS were first grafted with the visible fluorescent pyrene (Pyr) moieties to prove conjugation by colocalization of the Vis/NIR fluorescence on the (single) EB-NS level. The same procedure was performed and validated with carboxyl group (COOH)-containing hydrosilanes. These groups can serve as generic handle for further (bio)functionalization of the EB-NS surface. Finally, folic acid (FA) was conjugated to these COOH-functionalized EB-NS to target folic acid receptor-expressing cancer cells. These results highlight the potential of this surface chemistry approach to modify EB-NS and enable targeted NIR imaging for biomedical applications

Dynamic Nuclear Polarization NMR of Low-γ Nuclei: Structural Insights into Hydrated Yttrium-Doped BaZrO 3

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