Thermoelectric power of the vitreous electrolyte (AgI) 0.79(Ag 2O.B 2O 3)

The authors have determined the thermoelectric power epsi of the high ionic conductivity glass (AgI) 0.79(Ag 2O.B 2O 3) 0.21; epsi is negative throughout the investigated T range, 320-500K. The heat of transport of the mobile Ag +, QAg, taken as the slope of the straight line fitting epsi versus 1/ T, is quite lower than the activation energy obtained from conductivity data, viz. QAg=2.81 kcal mole -1< Eact=4.34 kcal mole -1. To circumvent this discrepancy, the analysis of the experimental data is carried out as follows: (i) it is supposed that QAg= Eact in agreement with the free ion theory for solid electrolytes; (ii) the vibrational part of the silver ion entropy, S(Ag +,vib), is assumed to be equal to the entropy of silver, S(Ag); (iii) on the ground of a structural model for this kind of glasses, the ideal configurational entropy of the mobile Ag +, S(Ag +,conf) id, is evaluated through a statistical approach. The ideal ionic entropy is defined as S(Ag +) id={ S(Ag +,vib)+ S(Ag +,conf) id}; (iv) the difference { S(Ag + ) exp- S(Ag +) id} is viewed as an excess entropy and is described according to the classical model of the regular solution