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The properties (superconducting and non-superconducting) of YBa2Cu3O7-δ bulk ceramics (YBCO) are strongly dependent on the oxygen deficiency, δ. Unfortunately, whether sintering or melt-processing is used to form the material, the final oxygen content is usually far from that which gives the optimum superconducting properties (δ≲0.1). Because of this, an additional oxygenation stage has to be carried out in which the material is heated and held at some elevated temperature (∼400–500 °C) for a significant time (often > 100 h) to allow oxygen to diffuse into the sample. Other diffusion-based processes (e.g. sintering) are known to be substantially enhanced in the presence of a microwave field, and it is reasonable to expect that the diffusion of oxygen into YBCO may also benefit from the application of such technology. The oxygenation of melt-processed YBCO using conventional and microwave-assisted heating has been compared. The diffusion coefficient at 400 and at 450 °C is shown to be enhanced by about 30% through the application of a high-frequency microwave field. Because the oxygenation time is inversely proportional to the diffusion coefficient, this represents a significant reduction in process time. The equilibrium value of the oxygen content is not affected by the application of a microwave field, and therefore the sample temperature must be the same for both microwave-assisted and conventional processing. Consequently, the observed enhancement is an example of a genuine non-thermal microwave effect.