Physico-Chemical nanomaterials science 

The effect of heterovalent dopants on ionic conduction in amorphous and nanocrystalline lithium heptagermanate
Trubitsyn M. P., Bochkova T. M., Koptiev M. M., Volnianskii M. D.
Institute for Energy Efficient Technologies and Materials Sciences, Oles Honchar Dnipro National University, Gagarina ave. 72, Dnipro-49010, Ukraine. 
E-mail: trubitsyn_m@ua.fm 

Electrical conductivity of lithium heptagermanate Li2Ge7O15 crystal is mainly determined by Li ions interstitials moving along the channels within Ge-O lattice framework [1]. Heterovalent doping with 3d-group ions (Mn, Cr) noticeably changes ionic conduction in Li2Ge7O15 crystal due to appearing charge compensating Li ions vacancies or interstitials [2]. Preparing amorphous and nanocrystalline Li2Ge7O15 compounds in [3] allowed to increase ionic conduction drastically as compared with crystal. At first combined influence of doping and nanometer structuring on ionic transport was studied in [4]. It was demonstrated that introducing small amounts of heterovalent dopants (Cr, Mn, Cu, Al, Gd) had only minor effect on ionic conduction in amorphous and nanocrystalline samples [4]. It was argued that in the disordered structures of glassy and nanocrystalline compounds there were much more weakly bound Li ions as compared with doped crystals. In this work we study ionic conduction in amorphous and nanocrystalline Li2Ge7O15 doped with heterovalent impurities which can be introduced in much higher concentrations than considered in [4]. Such dopants cause presence of non-stoichiometric excess Li ions which weakly bound to Ge-O structural framework and notably increase conductivity.

1.	Volnianskii M.D., Trubitsyn M.P., Obaidat YAH. Anisotropy of the electrical conductivity of lithium heptagermanate crystals // Phys Sol State.-2008.-50, N  3.-P. 422-424.
2.	Trubitsyn M.P., Volnianskii M.D., Obaidat Yahia AH. Ionic conduction in Li2Ge7O15 crystals doped with Cr and Mn ions // Phys Sol State.-2008.-50, N 7.-P. 1234-1237.
3.	Nesterov O., Trubitsyn M., Petrov O., et al. Conductivity and 7Li NMR Spin-Lattice Relaxation in Amorphous and Nano- and Microcrystalline Li2O-7GeO2// Nanocomposites, Nanostructures, and Their Applications. Springer Proc in Physics. - 221, chapter 6.-2019.- P.85-96.
4.	Trubitsyn M., Koptiev M., Volnianskii M. Ionic Conductivity in Single Crystals, Amorphous and Nanocrystalline Li2Ge7O15 doped with Cr, Mn, Cu, Al, Gd. Springer Proceedings in Physics, 2022, in press.