Millimeter-Wave Processing of LaCrO₃ and LaNiO₃ Perovskites Using 28 GHz Frequency

Both Cr₂O₃ and NiO absorb 28 GHz millimeter-wave energy well and this strong coupling with millimeter-waves can be used to promote a chemical reaction with La₂O₃ to form perovskite-type LaCrO₃ or LaNiO₃ ceramics. In La ₂O₃-Cr₂O₃ system, the reaction proceeded rapidly and single phase LaCrO₃ could be synthesized within 15 min even at lower temperature (∼400°C) as compared to conventional synthesis (T > 800°C). In the case of LaNiO₃, the reaction proceeded rapidly in the early stage of heating (t < 15min), but not completed even after prolonged millimeter-wave irradiation. The results suggest an importance of millimeter-wave penetration depth, especially for processing of conductive materials.