Radiofrequency and Microwave Dielectric Properties of Plasma Sprayed and Annealed Thick Layers of Titanium Dioxide

Titanium dioxide (TiO 2 ) was plasma sprayed using a high feed-rate spray system with hybrid water–argon stabilization torch (WSP-H). TiO 2 powder agglomerated from nanometric particles was used as the feedstock. The produced coating had thickness over 4 mm, to be comparable with bulk ceramic bodies. The deposit was removed from the substrate and annealed in air to reoxidize the oxygen deficient as-sprayed titania and to obtain material with a proper dielectric behavior. Besides the microstructure studies, radiofrequency dielectric spectroscopy and microwave dielectric spectroscopy were in the focus of investigation. The approach to annealing of an extremely thick coating is studied: The significance of annealing of a large-area thick coating is discussed, as the role of grain interior and grain boundaries in the charge transport is influenced. Relative permittivity ε r 94 and the Q*f product 12,800 GHz were reached at frequency 4 GHz, whereas the frequency response under 1 MHz was mapped continuously and the values (i.e., low and stable loss tangent) confirmed that a sprayed and air-annealed TiO 2 is able to approach or also overperform dielectric parameters typical for TiO 2 sintered bulk.