, Volume 20, Issue 5, pp 1763-1772

Electrical conduction in some important copper based superionic solids

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Measurement of the thermoelectric power (S) and electrical conductivity (σ) of six superionic solids namely CuI, CuPb3Br7, Cu2HgI4, Cu3CdI5, Cu3RbCl4, Cu7(C6H12NH3)Br8 and Cu16Rb4I7Cl13 are reported from 300 K to nearly the melting point of each material. The logσ T andS againstT −1 plots are linear in some temperature ranges with different slopes. For each material they show two distinct regions: one corresponding to superionic (SP) and the other to normal phase (NP). In the superionic phase, Cu+ ions are the main entity of charge carrier and an extended lattice gas model explains the transport mechanism fairly well. On the higher temperature side of SP, the other cation in the material starts contributing significantly toσ. In the normal phase the conduction is mainly due to Frenkel defects (Cu+ ions at interstitial sites). The enthalpy for migration and heat of transport of these defects has also been evaluated for CuI, CuPb3Br7, Cu2HgI4 and Cu3CdI5. The formation energy of defects has also been calculated for CuI and Cu3CdI5. Normal phase has not been obtained in Cu3RbCl4, Cu7(C6H12NCH3)Br8 and Cu16Rb4I7Cl13 as their phase transition temperatures lie below room temperature.