High temperature phase chemistry of system Eu-Pd-O

An isothermal section of the phase diagram for the system Eu - Pd - O at 1223 K has been established by equilibration of samples representing 20 different compositions, and phase identification after quenching by optical and scanning electron microscopy, X-ray powder diffraction, and energy dispersive spectroscopy. Three ternary oxides, Eu4PdO7, Eu2PdO4, and Eu2Pd2O5, were identified. Liquid alloys and the intermetallic compounds EuPd2 and EuPd3 were found to be in equilibrium with EuO. The compound EuPd3 was also found to coexist separately with Eu3O4 and Eu2O3. The oxide phase in equilibrium with EuPd5 and Pd rich solid solution was Eu2O3. Based on the phase relations, four solid state cells were designed to measure the Gibbs energies of formation of the three ternary oxides in the temperature range from 925 to 1350 K. Although three cells are sufficient to obtain the properties of the three compounds, the fourth cell was deployed to crosscheck the data. An advanced version of the solid state cell incorporating a buffer electrode with yttria stabilised zirconia solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode was used for high temperature thermodynamic measurements. Equations for the standard Gibbs energy of formation of the interoxide compounds from their component binary oxides Eu2O3 with C type structure and PdO have been established. Based on the thermodynamic information, isothermal chemical potential diagrams and isobaric phase diagrams for the system Eu - Pd - O have been developed.

Phase relations in the system Cu-Eu-O and thermodynamic properties of CuEu2O4 and CuEuO2

Phase relations in the system Cu-Eu-O have been determined by equilibrating samples of different average composition at 1200 K and by phase analysis after quenching using optical microscopy (OM), x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray (EDX). The equilibration experiments were conducted in evacuated ampoules and under flowing inert gas and pure oxygen. The Cu-Eu alloys were found to be in equilibrium with EuO. The higher oxides of europium, Eu3O4 and Eu2O3, coexist with metallic copper. Two ternary oxides CuEu2O4 and CuEuO2 were found to be stable. The ternary oxide CuEuO2, with copper in the monovalent state, can coexist with Cu, Cu2O, Eu2O3 and CuEu2O4 in different phase fields. The compound CuEu2O4 can be in equilibrium with Cu2O, CuO, CuEuO2, Eu2O3, and O2 gas under different conditions at 1200 K. Thermodynamic properties of the ternary oxides were determined using three solid-state cells based on yttria-stabilized zirconia as the electrolyte in the temperature range from 875 to 1250 K. The cells essentially measure the oxygen chemical potential in the three-phase fields: Cu+Eu2O3+CuEuO2, Cu2O+CuEuO2+CuEu2O4, and Eu2O3+CuEuO2+CuEu2O4. The thermodynamic properties of the ternary oxides can be represented by the equations: $\begin{gathered} {\raise0.5ex\hbox{$Couldn't find \end for begin{gathered} Thermogravimetric analysis (TGA) studies in Ar+O2 mixtures confirmed the results from emf measurements. An oxygen potential diagram for the system Cu-Eu-O at 1200 K was evaluated from the results of this study and information available in the literature on the binary phases.