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Cuprous oxide (Cu2O) is actively studied as a prototypical material for energy conversion and electronic applications. Here we reduce the growth temperature of phase pure Cu2O thin films to 300 °C by intentionally controlling solely the kinetic parameter (total chamber pressure, Ptot) at fixed thermodynamic condition (0.25 mTorr pO2). A strong non-monotonic effect of Ptot on Cu-O phase formation is found using high-throughput combinatorial-pulsed laser deposition. This discovery creates new opportunities for the growth of Cu2O devices with low thermal budget and illustrates the importance of kinetic effects for the synthesis of metastable materials with useful properties.

Acceptor‐doped barium cerate perovskite oxides act as high temperature proton conducting ceramics, which can be utilized in solid oxide fuel cells, hydrogen separation membranes, and other electrochemical devices. One of the major issues in their fabrication is the formation of second phases during sintering of these perovskite oxides. In this work, the formation of a second phase is investigated with an aim to understand its influence on the properties of the parent perovskite oxide and also the necessity for its removal. BaCe0.8Y0.2O3−δ (BCY20) was synthesized via a polymeric sol–gel method and characterized by X‐ray diffraction, scanning electron microscopy, and micro‐Raman spectroscopy. Formation of the second phase on the surface of the sintered pellets (sintering temperature >1250°C for 24 h) was identified to be yttria‐doped ceria (Y0.2Ce0.8O1.9). A mechanism for the formation of the second phase is proposed. The formation of second phase was prevented by sintering the pellets in a powder bath of the same composition as the parent perovskite oxide. From impedance spectroscopy measurements of pellets sintered with and without the powder bath, it was found that the second phase (in the pellet sintered without powder bath) has a negative effect on the bulk ionic conductivity of the pellet.

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