A laser heating study of the CeO2 solid/liquid transition: challenges related to a refractory compound with a very high oxygen pressure

A laser heating technique is employed to study the melting behaviour of cerium dioxide, CeO2, a refractory compound with very high oxygen pressure. The strong tendency of cerium dioxide to reduce to hypostoichiometric compounds, even in the presence of trace amounts of oxygen, leads to discrepancies in the measured melting temperature depending on whether an oxidising, neutral or reducing atmosphere is used during the experiment. The purpose of this study is to measure the melting temperature of initially stoichiometric CeO2 under different controlled atmospheres: reducing or oxidizing. A high pressure cell was used to limit the oxygen losses while measuring the melting behaviour of initially stoichiometric cerium dioxide samples. The results confirm a strong influence of the atmosphere on the melting temperature: when reducing conditions were simulated a melting temperature of (2675 ± 47) K was measured, in oxidizing conditions it was measured (2743 ± 33) K. The measured values are in line with existing literature data obtained under different conditions. Only under a high buffer gas pressure, He at 15 MPa the highest reported temperature of 3000 K was observed here, although with poor repeatability.