57Fe-Mossbauer spectra of superconducting beta-FeSe, the Li/NH3 intercalate product and a subsequent sample of this intercalate treated with moist He gas have been measured in temperature range 4.7 - 290 K. A correlation is established between hyperfine parameters and critical temperature Tc in these phases. A strong increase of isomer shift upon intercalation is explained by a charge transfer from the Li/NH3 intercalate to the FeSe layers resulting in an increase of Tc up to 42 K. A significant decrease of the quadrupole splitting above 240 K has been attributed to diffusive motion of Li+ ions within the interlamellar space.
@article{arxiv.1511.04393,
title = {Intercalation effect on hyperfine parameters of Fe in FeSe superconductor with Tc = 42 K},
author = {Sergii I Shylin and Vadim Ksenofontov and Stefan J Sedlmaier and Simon J Clarke and Simon J Cassidy and Gerhard Wortmann and Sergey A Medvedev and Claudia Felser},
journal= {arXiv preprint arXiv:1511.04393},
year = {2015}
}