Phases, phase transitions and excitons of the superionic conductor Cu2HgI4, from 4.2 K to 373 K, as revealed by the Kubelka-Munk spectral function

The Kubelka-Munk spectral function of Cu 2 HgI 4 powder was determined between 4.2 and 373 K. The logarithms of the integrated spectra versus inverse temperature gave a function which confirmed the existence of two reported phases and revealed three unreported ones. The logarithms of the frequencies of each of the two homologous points, each of them at one of the two edges of the spectra, versus inverse temperature, confirmed these findings. The relevant phase transition temperatures were determined. At 337 K or below, each phase produced at least one characteristic prominent exciton emission. On lowering the temperature sufficiently (T ≤74 K), many exciton emissions appeared, particularly in an isothermally formed phase at 4.2 K.