Synthesis, Crystal Structure and Lithium Motion of Li8SeN2 and Li8TeN2

In material sciences, spectroscopic approaches combining ab initio calculations with experiments are commonly used to accurately analyze the experimental spectral data. Most state-of-the-art first-principles calculations are usually performed assuming an equilibrium static lattice. Yet, nuclear motion affects spectra even when reduced to the zero-point motion at 0 K. We propose a framework based on density-functional theory that includes quantum thermal fluctuations in theoretical x-ray absorption near-edge structure (XANES) and solid-state nuclear magnetic resonance (NMR) spectroscopies and allows to well describe temperature effects observed experimentally. Within the Born-Oppenheimer and quasiharmonic approximations, we incorporate the nuclear motion by generating several nonequilibrium configurations from the dynamical matrix. The averaged calculated XANES and NMR spectral data have been compared to experiments in MgO. The good agreement obtained between experiments and calculations validates the developed approach, which suggests that calculating the XANES spectra at finite temperature by averaging individual nonequilibrium configurations is a suitable approximation. This study highlights the relevance of phonon renormalization and the relative contributions of thermal expansion and nuclear dynamics on NMR and XANES spectra on a wide range of temperatures

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“…Then, each x µ is multiplied by the corresponding normal length a µ , as defined in Eq. (16). The set of sogenerated normal coordinates…”

Section: A Quasi-harmonic Vibrationsmentioning

confidence: 99%

Phonon effects on x-ray absorption and nuclear magnetic resonance spectroscopies

et al. 2015

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“…In this case, the automatic T/M capability of the ATMC probe approach enables a straightforward detection of the huge spectral width by automated frequency sweep (also known as frequency step [47]) experiments over 1 MHz in 10 kHz steps applying selective pulses ( Figure S7, Experimental Section). This technique is well known for significantly broadened line shapes of quadrupolar nuclei [46,[48][49][50][51] and other kinds of so-called ultra-wideline NMR spectra covering frequency ranges of approx. 250 kHz to tens of MHz [47,52].…”

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confidence: 99%

Automatic Tuning Matching Cycler (ATMC) in situ NMR spectroscopy as a novel approach for real-time investigations of Li- and Na-ion batteries

Pecher

Bayley

Líu

et al. 2016

Journal of Magnetic Resonance

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We have developed and explored the use of a new Automatic Tuning Matching Cycler (ATMC) in situ NMR probe system to track the formation of intermediate phases and investigate electrolyte decomposition during electrochemical cycling of Li- and Na-ion batteries (LIBs and NIBs). The new approach addresses many of the issues arising during in situ NMR, e.g., significantly different shifts of the multi-component samples, changing sample conditions (such as the magnetic susceptibility and conductivity) during cycling, signal broadening due to paramagnetism as well as interferences between the NMR and external cycler circuit that might impair the experiments. We provide practical insight into how to conduct ATMC in situ NMR experiments and discuss applications of the methodology to LiFePO4 (LFP) and Na3V2(PO4)2F3 cathodes as well as Na metal anodes. Automatic frequency sweep (7)Li in situ NMR reveals significant changes of the strongly paramagnetic broadened LFP line shape in agreement with the structural changes due to delithiation. Additionally, (31)P in situ NMR shows a full separation of the electrolyte and cathode NMR signals and is a key feature for a deeper understanding of the processes occurring during charge/discharge on the local atomic scale of NMR. (31)P in situ NMR with "on-the-fly" re-calibrated, varying carrier frequencies on Na3V2(PO4)2F3 as a cathode in a NIB enabled the detection of different P signals within a huge frequency range of 4000 ppm. The experiments show a significant shift and changes in the number as well as intensities of (31)P signals during desodiation/sodiation of the cathode. The in situ experiments reveal changes of local P environments that in part have not been seen in ex situ NMR investigations. Furthermore, we applied ATMC (23)Na in situ NMR on symmetrical Na-Na cells during galvanostatic plating. An automatic adjustment of the NMR carrier frequency during the in situ experiment ensured on-resonance conditions for the Na metal and electrolyte peak, respectively. Thus, interleaved measurements with different optimal NMR set-ups for the metal and electrolyte, respectively, became possible. This allowed the formation of different Na metal species as well as a quantification of electrolyte consumption during the electrochemical experiment to be monitored. The new approach is likely to benefit a further understanding of Na-ion battery chemistries.

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“…[11] A similar range of shift values for Li atoms has recently been reported, for example, for the Li + -ion conductor Li 7Àx PS 6Àx I x [12] and for the compounds Li 8 XN 2 with X = Se, Te. [13] The observed composition range of the clathrate phase can be understood in terms of the Zintl-Klemm concept. In a Ge 46 framework all Ge atoms are four-bonded and thus electronically saturated.…”

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confidence: 99%