Study on the Defect Structure of SnO₂:F Nanoparticles by High-Resolution Solid-State NMR

Abstract

In this contribution the preparation and structural characterization of nanoscale fluorine doped tin-oxide (SnO2:F, FTO) is described. By using a microwave assisted polyol approach, nanoparticles with different doping levels are prepared, which show narrow size distribution as measured by X-ray diffraction, electron microscopy and dynamic light scattering. They were converted into electrically conductive optically transparent films at 500 °C by a specific thermal treatment (500 °C in air followed by 250 °C in forming gas), exhibiting a specific resistivity of (1.9 × 10−1 Ω cm). Solid-state MAS NMR and 119Sn Mössbauer spectroscopy were used to study how F atoms are incorporated into the SnO2:F nanoparticles. Distance constraints were determined by 119Sn{19F} REDOR, fluorine-doping homogeneity by homonuclear dipolar recoupling experiments (SR66 2). Cross-polarization was used to investigate the immediate environment of the dopant. The experiments were supplemented by first-principles quantum-chemical calculations for possible defect site models. The combined data strongly indicate that F doping is not directly related to an increase in charge-carrier concentration, even though F atoms do occupy O vacancy sites in SnO2:F. For this study we have implemented background compensated NMR 2D pulse-sequences which reliably suppress the fluorine background originating from the NMR probe. Moreover we show that cluster calculations on the basis of the extended embedded ion method (EEIM) can be used to study the structure of diluted defects in crystalline host structures and predict NMR properties.

Highly efficient electrochemical degradation of perfluorooctanoic acid (PFOA) by F-doped Ti/SnO2 electrode

“…Maybe they considered that Ti/SnO 2 material only prepared by SnCl 4 would still possess low conductivity like pure SnO 2 . In fact, SnO 2 coating undoped by Sb is likely to form oxygen vacancies due to non-stoichiometric generation during rapid crystal growth; and it is quite possible that some O vacancies were filled by residual chlorine from SnCl 4 precursor [21,22].…”

“…Moreover, the presence of interstitial Fˉ would also increase the lattice disorder remarkably [22,29,43], decreasing the chemical stability of electrode. In fact, many reports about F-doped SnO 2 film as TCO have used a range of analytical tools to verify that proper Fˉ doping in the enormous O vacancies of SnO 2 lattice increased carrier concentrations and thus decreased the sheet resistance [22,26,44]; however, excess F doping, residing in interstitial sites at the grain boundary region or in dopant clusters, could hinder the electron transport through the grain boundary and increase carrier scattering, thus causing the increase of the resistivity [29,32,42,43].…”

Structural investigation of aluminium doped ZnO nanoparticles by solid-state NMR spectroscopy

“…The experiment used CX 1 X symmetries and a post-C-element 45,46 that corresponds to a 1 H nutation frequency n rf of 50 kHz at n MAS of 25 kHz. The C-REDOR data were plotted as DS/S 0 against the universal dephasing time t uds , 47,48 which is a pulse sequence-independent time scale defined by the product |k|t of the magnitude of the scaling factor k and the dipolar dephasing time t. The scaling factor 49 H during extra p/2 À t 1 À p/2 block, which is followed by a short zero-quantum filter of a few ms. Proton decoupling was implemented using continuous wave (cw) decoupling with a rf field strength corresponding to 100 kHz. The nutation frequency for the selective pulses applied to the 27 Al central transition was 50 kHz.…”

“…the electric field gradient tensor (EFG, q) and the absolute magnetic shielding tensor s. To this end we made use of the Extended Embedded Ion Method (EEIM), 64 an embedded cluster approach derived from the Embedded Ion Method (EIM), 65,66 whose basic feature is the embedding of the quantum cluster (QC) in a self-consistent point charge field that simulates the environment of an ideal crystal in the electrostatic approximation, which is well suited to the treatment of doped materials at low doping levels. 48 Because the EFG as well as the chemical shift is a local quantity, 67 embedded cluster methods are also suitable for its calculation. 68 For doped crystals we propose a two-step procedure analogous to the one for s described in ref.…”

“…68 For doped crystals we propose a two-step procedure analogous to the one for s described in ref. 48: in the first step, the embedding point charges are obtained for an ideal (i.e. non-defective) crystal/QC, where the usual self-consistent procedure of EEIM as described in ref.…”