Crystallization of Na3VTi(PO4)2F3 glass: In situ observation of the function of distribution of relaxation times

Abstract

In situ, temporal alteration of broadband impedance spectra of glassy mixed ionic-electronic conductor Na3VTi(PO4)2F3 was studied by heat treating the sample in the vicinity of glass transition temperature (Tg=740K). Several relaxation processes of charge carriers were identified in the spectra, and the method of distribution of relaxation times (DRT) was used to analyze them. The single moderately broad DRT bell-shaped peak was observed at the beginning of the temporal evolution, related to the only relaxation process in the initial glassy phase. Over time, the peak shifted towards higher relaxation times τ, broadened, and split up into a double, and the third broader peak also appeared at the far region of lower τ. After 7 h, the double peak acquired a relatively regular bell shape and was considered to represent the crystalline phase. The evolution of the DRT over 7 h was shown by fitting the prominent DRT double peak to two distinct Gaussian bells. The time dependency of the mixed glassy-crystalline sample's phase composition was determined by the mentioned Gaussian fits. The third peak was attributed to the relaxation process in the inter-grain area.