It was noted that whereas the structures of Na2UBr6 and Na2UCl6, as studied using neutron diffraction, were very similar the structures of the other halides were different. That of Li2UI6 exhibited a feature which was also found in Na2UI6. That is, both compounds exhibited so-called empty layers which could be considered to be conduction planes for current carriers. It was thought that these layers could partially fill with Li+, as the temperature was increased, thus facilitating the conduction of Li ions. Some of the studied compounds, such as Li2UI6, appeared to undergo phase transitions to a high-conductivity state.

K.Maletka, E.Ressouche, W.Szczepaniak, L.Rycerz, A.Murasik: Materials Science Forum, 1996, 228-231, 711-6