The thermoelectric power in AgxTiS2 and AgxNiPS3. Part II. The ionic component of the thermoelectric power
The EMF of the isothermal cells: Ag/AgI/AgxTiS2: 0<x<1, T=150–200°C/AgxNiPS3: 0<x<3, T=150–350°C has been measured. From the EMF-x curves the existence ranges of the 2-phase (stage I and II) regions −0.16<x<0.32 for the Ag/AgxTiS2 system at 190°C; 0.20 < x < 0.50 and 1 < x < 2 for the Ag/AgxNiPS3 system at 400°C - have been determined. The results are sustained by X-ray diffraction and electrical conductivity measurements. From the EMF-T curves the partial enthalpy (ΔHAg) and entropy (ΔSAg) of dissolution of silver in the AgxSSE (solid solution electrode) materials were obtained. In the case of AgxTiS2, ΔHAg has a low absolute value, while ΔSAg is distinctly positive. The EMF of the Ag/AgxNiPS3 system also has a positive temperature coefficient. Furthermore, the ionic component of the thermoelectric power, ΔE/ΔT, of the thermogalvanic cells: Ag/AgI/AgxSSE/AgI/Ag AgxTiS2: 0 < x < 1, T = 150–200°C( T ) (T+ΔT) AgxNiPS3: 0 < x < 1, T= 150–350°C has been measured. The kinetically important heat of transport of silver ions in the AgxSSE materials has been determined in two ways: first from the dependence of the ionic Seebeck coefficient (ϵAg+) on reciprocal temperature; and second from direct calculation, using the data for ϵAg+ and ΔSAg. The heat of transport is much smaller than the activation enthalpy for Ag+-conduction, indicating a high ionic polaron binding energy in these materials.