“Glassy” properties of crystalline Li3N at low temperatures

We have studied the acoustic and dielectric behaviour of the superionic conductor Li₃N at temperatures between 100 K and 20 mK. At low temperatures its properties are determined by low-energy excitations similar to those observed in glasses. In Li₃N these excitations are ascribed to the tunneling of hydrogen impurities, whereas thermally activated hopping of lithium ions accounts for the behaviour at higher temperatures.