On the microwave-heating behavior of acceptor- and donor-type substituted CeO2

Microwave irradiation has been demonstrated unambiguously in several literature studies to lead to the reduction of ceria-based metal oxides. Various explanations have been put forward, but as of yet no consensus has been reached. In this study, we present experimental results that may contribute to the understanding of the microwave heating behavior of ceria-based metal oxides. Based upon this, we propose a defect chemical mechanism centered around the electronic structure of the material and its interaction with the electromagnetic field. To test this hypothesis, we prepared a set of acceptor- and donor-type substituted ceria samples and quantified their thermal response towards microwave irradiation. We found, that the nature of the substituent greatly influences the microwave heating properties in CeO2 in respect to the heating rate and the extent of the stable temperature regime. While the introduction of oxygen vacancies by use of acceptor-type Gd-substitution did not affect both parameters significantly, the use of Ni as substituent dramatically improved the conversion of electromagnetic energy to heat. On the other hand, donor-type substitution by Nb-introduction completely suppressed the unstable temperature regime and not a single thermal runaway was observed in Nb-substituted CeO2 samples, even at relatively high temperatures and field strength. We believe, these results can contribute to the understanding of the complex microwave-solid interaction and lead to oxide materials with tailored heating properties.