An assessment of the silver–oxygen system has been made, and a consistent set of thermodynamic parameters has been optimized. The calculated thermodynamic properties and phase relations are in good agreement with the experimental data. Ag2O is the only phase that is commonly found within the system. In air, it decomposes to silver and oxygen gas at 420 K. There is a eutectic between silver and Ag2O at a temperature of 804 K, an oxygen partial pressure (PO2) of 526 bar (5.26 × 107 Pa), and an oxygen mole fraction in the liquid phase of 0.25. Uncertainties remain on the Ag2O liquidus for PO2 > 108 Pa. An ionic two‐sublattice model has been used to describe the liquid phase. This work is part of a study of interactions between compounds from the bismuth‐strontium‐calcium‐copper‐oxygen system and silver.

2 by DTA. There are no ternary phases stable at ambient pressure. Presently measured transformation temperatures have been combined with existing oxygen activity measurements in the metal liquid to optimize thermodynamic parameters describing the liquid phase. The resulting fit is excellent. EDX measurements of the composition in the oxide liquid have a rather low precision but confirm the thermodynamic optimization. However, some uncertainties remain concerning the liquid composition at the eutectic transformation and the shape of the miscibility gap at higher temperatures.

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The phase relations in the silver‐strontium‐copper‐oxygen (Ag‐Sr‐Cu‐O) and silver‐calcium‐copper‐oxygen (Ag‐Ca‐Cu‐O) systems were studied in oxygen, air, and nitrogen environments, using differential thermal analysis and energy‐dispersive X‐ray spectrometry. The presence of silver reduces the melting temperature of the oxide liquid to a monotectic in the strontium‐ and calcium‐containing systems by 62 and 82 K, respectively (to 1222 and 1244 K, respectively) in oxygen. The oxide liquid dissolves silver (up to a metallic ratio of 0.17) in the Ag‐Sr‐Cu‐O system in oxygen at a temperature slightly higher than that required for monotectic reaction. In the Ag‐Ca‐Cu‐O system, the silver content has been measured to be 0.29 (metallic ratio). The oxide systems have been optimized using the experimental data from monotectics and those from lower‐order systems that have been published previously. This work is part of a project to evaluate the phase relations within the silver‐bismuth‐strontium‐calcium‐copper‐oxygen (Ag‐Bi‐Sr‐Ca‐Cu‐O) system and, in particular, to focus on the influence of silver on the phase equilibria around the superconducting phases during partial‐melt processing.