Abstract
Barium titanate coatings were, for the first time, sprayed by a high feed-rate plasma torch with water stabilization of the plasma. Two power levels of the torch were applied for spraying to cover steel substrates. Various substrate preheating levels from 125 °C to 377 °C were used to modify cooling conditions. Microstructure and phase composition including crystallinity quantification were observed. Dielectric measurements proved that the relative permittivity between 300 and 400 coatings is too temperature sensitive over 170 °C but fits the requirements of the EIA temperature coefficient between room temperature and 170 °C. Simultaneously, the loss tangent remains rather low, between 0.02 and 0.07, in a broad range of temperatures and frequencies. Annealing was performed in air to heal the oxygen deficiency, but only modified the microstructure insignificantly. The dielectric properties of as-sprayed and annealed samples were discussed, with the main finding that the temperature coefficient of permittivity was improved by annealing. This study contributes to the search for the suitability of plasma-sprayed BaTiO3 coatings for application in the electrical industry, namely by the optimization of conditions for high feed-rate spraying.
Highlights
Barium titanate BaTiO3 is the longest existing ferroelectric perovskite material, a ceramic with a series of structural phase transitions [1]
Dielectric measurements proved that the relative permittivity between 300 and 400 coatings is too temperature sensitive over 170 ◦C but fits the requirements of the Electronic Industries Alliance (EIA) temperature coefficient between room temperature and 170 ◦C
The goal of this paper is to show how the substrate temperature influences the dielectric parameters of the as-sprayed BaTiO3, and how the dielectric parameters and their stability are further modified by annealing
Summary
Barium titanate BaTiO3 is the longest existing ferroelectric perovskite material, a ceramic with a series of structural phase transitions [1]. Due to its high relative permittivity and low dielectric loss tangent, barium titanate is most typically used in capacitors, but frequently in other energy-storage devices. Coatings with thicknesses between 10 μm and 1 mm are considered thick films [2,3]. The properties of these layered structures are usually considered to be comparable with bulk materials, but various aspects of the rapid solidification of thermally sprayed thick films influence their microstructure and properties. A value of relative permittivity of about 2500 was reported for plasmasprayed barium titanate, but the loss tangent of these samples was high, at about 0.45 [5]. The net dipole moment of BaTiO3 bulk has a value of 26 μC/cm2 [10]
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