The role of amorphous phase content on the electrical properties of atmospheric plasma sprayed (Ba,Sr)TiO₃ coatings

(Ba,Sr)TiO₃ coatings deposited on carbon steel substrates were successfully prepared by an atmospheric plasma spray system. Three sets of samples containing different amount of both crystalline and amorphous phases were deposited and consequently studied in order to determine their electrical properties. The results show a clear correlation existing between the amorphous phase content and coatinǵs electrical properties. The resistivity increases with increase of amorphous phase content. Relative permittivity for low frequencies decreases and become more stable with frequency tuning when amorphous phase content increased. The maximum relative permittivity value is in the range 75-200 for frequency 1 kHz. The loss factor varies between 0.23 and 0.03 for all studied samples. The loss factor is at the lower limit of these values and frequency much less dependent when the coating contains 15 wt% of amorphous phase and more. The band gap of all samples is between 2.75 eV and 2.90 eV. Microstructure and hardness were evaluated in order to determine basic mechanical properties of deposits.