# System Bi–Sr–O: Synergistic measurements of thermodynamic properties using oxide and fluoride solid electrolytes

Jacob, KT and Jayadevan, KP (1998) System Bi–Sr–O: Synergistic measurements of thermodynamic properties using oxide and fluoride solid electrolytes. In: Journal of Materials Research, 13 (7). pp. 1905-1918.

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Phase equilibrium and electrochemical studies of the ternary system Bi-Sr-O indicate the presence of six ternary oxides ($Bi_2SrO_4$, $Bi_2Sr_2O_5$, $Bi_2Sr_3O_6$, $Bi_4Sr_6O_1_5$, $Bi_1_4Sr_2_4O_5_2$, and $Bi_2Sr_6O_1_1$) and three solid solutions (\delta, \beta, and \gamma). An isothermal section of the phase diagram is established at 1050 K by phase analysis of quenched samples. Three compounds, $Bi_4Sr_6O_1_5$, $Bi_1_4Sr_2_4O_5_2$, and $Bi_2Sr_6O_1_1$, contain $Bi^5^+$ ions. The stability of these phases is a function of oxygen partial pressure. The chemical potentials of SrO in two-phase fields are determined as a function of temperature using solid-state cells based on single crystal $SrF_2$ as the electrolyte. Measurement of the emf of cells based on $SrF_2$ as a function of oxygen partial pressure in the gas at constant temperature gives information on oxygen content of the compounds present at the electrodes. The chemical potentials of $Bi_2O_3$ in two-phase fields of the pseudobinary $Bi_2O_3-SrO$ are measured using cells incorporating ($Y_2O_3$)$ZrO_2$ as the solid electrolyte. The standard free energies of formation of the ternary oxides are calculated independently using emfs of different cells. The independent assessments agree closely; the maximum difference in the value of \Delta $G_f$ degrees ($Bi_2_mSr_nO_p$)/(m + n) is \pm 350 J/mol of component binary oxides. The results are discussed in the light of the phase diagram and compared with calorimetric and chemical potential measurements reported in the literature. The combined use of emf data from cells incorporating fluoride and oxide electrolytes enhances the reliability of derived data.