Thermoelectric Power and Thermal Diffusion in Cubic Lithium Sulfate

The thermocell Pt/Li2S04 /Pt has been studied over the temperature range 580 —820 °C. The initial thermal emf of —0.7 mV/degr. is identified as the inhomogeneous thermoelectric power due to the temperature dependence of the salt/metal contact potential. Thermal diffusion increases the number of cations at the cold electrode. This causes a change in the thermal emf for which the characteristic time is found to be inversely proportional to the self-diffusion coefficient of the lithium ions. The total steady-state thermoelectric power is temperature-dependent £ o c = (0.03 ± 0.25) + (1.95 ±0 .34 ) • 10~3 Tm mV/degr. where Tm is the mean absolute temperature and the errors are standard deviations. The thermocell Zn/Li2S04 /Zn was found to have the same initial emf within experimental error.