The
first discharge of a nanostructured FeSn2 based
negative electrode for Li-ion batteries has been studied by combining
operando 119Sn Mössbauer spectroscopy and ex situ magnetic measurements. A modified Swagelok-type
cell has been designed to perform in situ Mössbauer
measurements, which allowed us to quantitatively follow the first
discharge. The electrochemical mechanism consists in a conversion
reaction that transforms FeSn2 into Li7Sn2. The Mössbauer spectrum at the end of the first discharge
has been analyzed from first principles calculations of the Mössbauer
parameters. The observed differences with bulk Li7Sn2 have been explained by the small size of the electrochemically
formed particles. The magnetic measurements of the electrode material
at the end of the discharge show the existence of rather pure superparamagnetic
iron nanoparticles with an average diameter in the range 2–3
nm as evaluated from three different methods. The electrode saturation
magnetization increases during the discharge, due to the increasing
number of formed iron nanoparticles, but unexpected two-step variations
were observed. They are interpreted by changes of the FeSn2 magnetization caused by interactions with iron nanoparticles.
This article is devoted to the thermal expansion of ZnSb combining experiments (neutron and x-ray) and calculations based on density functional theory. Related properties are also studied such as: the zone-center (Raman and infrared) phonon modes, the dielectric (electronic and static) tensors, the phonon density-of-states, the specic heats and the isotropic atomic displacement parameters. Our experimental data show highly anisotropic thermal expansion with large values along the a-direction. Concomitantly, a large increase of the Zn-Zn intra-ring distances and of one of the intra-ring Zn-Sb distances is observed, while other interatomic distances do not signicantly change. In agreement with our calculations, the thermal expansion has positive values along the three crystal directions except around 30 K where it has weak negative values along the b and c-directions. This anomalous expansion is more important along the c-direction and it is mainly due to phonon modes with frequencies up to 75 cm −1 . These modes are located in the S − Y − Γ (resp. Γ − Z) q-point range along the b (resp. c) direction. Phonon modes located in the Γ−X and in the Y − Γ − Z q-point range with frequencies up to 175 cm −1 are responsible for the positive large thermal expansion at room temperature along the a-direction. The much reduced anisotropy of the thermal conductivity is related to the lower Debye temperatures along the b and c-directions and mainly to the small transverse sound velocity between these directions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.