IONIC-CONDUCTIVITY IN SINGLE-CRYSTAL PROUSTITE AG3ASS3

The temperature dependent ac conductivity of single-crystal proustite measured at several frequencies over the temperature range from 82 to 467 K reveals six distinct regions associated with different conduction mechanisms. A phase transition from ionic to superionic conduction has been found to occur at a temperature of approximately 420 K. The frequency dispersion spectra obtained at different temperatures from 82 to 373 K, over the frequency range 10(-2) to 10(3) Hz show two regions of frequency dependent conductivity. The dc conductivity and ionic hopping rate as well as the carrier densities have been extracted from the ac conductivity data. The results show that the ac conductivity of proustite is characterized by low hopping rates and high carrier densities suggesting that the Ag+ ions may execute a long range hopping motion in the lattice. The relationship between the dc and ac components of conductivity have been critically examined and the results show that the ratio sigma-dc/sigma-ac is thermally stimulated with an activation energy n-DELTA-H(m), where DELTA-H(m) is the enthalpy of ion migration, and n is the slope of the conductivity dispersion curve.