POTENTIOMETRIC DETERMINATION OF THE THERMODYNAMIC STABILITY OF SRO-RUO2 SYSTEM

A partial phase diagram for SrO-RuO2 system in the temperature range 1023 to 1473K under 1 atmosphere of oxygen was determined for the purpose of galvanic cell studies. The e.m.f. of the galvanic cells using 15 wt.% CaO-stabilized ZrO2 (15 CSZ) solid electrolyte and air (P(O2) = 0.21 atm)/Pt as the reference electrode yielded the following least-squares expressions for the test electrodes SrO/Sr2RuO4/Ru (I), Sr2RuO4/Sr3Ru2O7/Ru (II) and Sr3Ru2O7/SrRuO3/Ru (III) over the temperature ranges 1044 to 1235, 926 to 1164 and 991 to 1282K respectively: E(I) = 1009.25 - 0.40411 T +/- 3.37 mV (1) E(II) = 1060.67 - 0.46896 T +/- 3.26 mV (2) E(III) = 1010.50 - 0.43449 T +/- 3.78 mV (3) These e.m.f. results, after correcting for the standard state of oxygen in the air reference electrode, were combined with the DELTAG(f)o(RuO2) from literature and the standard Gibbs energies of formation, DELTAG(f, ox)o, of Sr2RuO4, Sr3Ru2O7 and SrRuO3 were determined.