Josef Sedlacek

Dielectric relaxation in calcium titanate-containing ceramics prepared by plasma spraying

Abstract The relative permittivity and loss factor frequency dependence in a weak electric field of plasma sprayed perovskite and ilminite polycrystalline ceramic materials—pure synthetic calcium titanate, as well as magnesium titanate—calcium titanate mixture, were studied. It was observed that plasma-sprayed titanates exhibit a strong relaxation of permittivity and loss factor decrease when they are measured in an as-sprayed state. The frequency dependence of the earlier properties is influenced by chemical composition and spraying parameters, but the relaxation character in general is preserved in all cases. The volume resistivity of the samples in an as-sprayed as well as subsequently annealed state was studied also. Several aspects of the structural features of plasma deposits and their possible influence on dielectric properties are discussed.

Dielectric properties of plasma sprayed titanates

Abstract This paper presents the study of the dielectric properties of three plasma-deposited titanates. The deposits were prepared from powders with the same starting composition as industrially produced dielectric ceramics. Influence of plasma spraying itself and of the subsequent annealing of sprayed deposits on electric resistivity, permittivity and the loss factor is reported. Pure synthetic perovskite (CaTiO 3 ) and two perovskite-related ceramic materials (MgTiO 3 –CaTiO 3 and LaMg 0.5 Ti 0.5 O 3 –CaTiO 3 ) were plasma sprayed to form specimens enabling various electric measurements. CaTiO 3 and their solid solution with LaMg 0.5 Ti 0.5 O 3 have perovskite crystal structure and MgTiO 3 have the ilmenite structure. Water-stabilized plasma gun WSP® as well as commercial APS (gas stabilized system) were used to form ceramic layers on stainless steel substrates as well as self-supporting ceramic discs. Surface of specimens was ground after spraying. Thin layer of aluminum as the counter-electrode was sputtered in reduced pressure on the ground surface. Micrometric capacitor and ASTM-convenient resistivity adapter were used for voltage applying. Permittivity and volume resistivity were calculated from the measured capacity and resistance respectively. Self-supporting ceramic deposits were annealed at two different temperatures below and above the sintering temperature of the given material. Properties dependence on annealing temperature was obtained and discussed in relation to porosity.

Influence of chemical composition on dielectric properties of Al2O3 and ZrO2 plasma deposits

Abstract Aluminum oxide, zirconium oxide and their mixture were plasma sprayed by a water-stabilized plasma gun. Resulting deposits were studied as dielectrics. Capacity and loss factor were measured for the frequency range 200–10 6 Hz and relative permittivity was calculated. Electric resistance was also measured and volume resistivity calculated for all studied materials. It was proved that dielectric behavior of plasma sprayed oxide ceramics like alumina- and zirconia-based materials at low voltage follows the expectations based on the knowledge of dielectric behavior of sintered ceramics.

Dielectric properties of CaTiO3 coatings prepared by plasma spraying

Abstract This paper presents a study of dielectric properties, namely the relative permittivity and loss factor dependence on the frequency of a weak electric field. Perovskite CaTiO3 was studied in the form of coatings and self-supporting plates made by plasma spraying. A conventional gas stabilised plasma gun (GSP) as well as a water stabilised plasma gun (WSP) were employed. It was observed that plasma sprayed titanates exhibit a strong relaxation of permittivity and loss factor decrease with a frequency rise. These properties are influenced by spray technique and spraying parameters, but the relaxation character in general is preserved in all cases. The volume resistivity of the samples was studied as well. Several aspects of the structural features of plasma deposits, especially the phase composition, porosity character, and their influence on dielectric properties are discussed.

Selected aspects of dielectric behavior of plasma sprayed titanates

XRD measurements were carried out on plasma sprayed titanates BaTiO3, CaTiO3, MgTiO3 and a mixture of the last two. Samples were tested as dielectrics and volume resistivities of the materials were also summarized. Microwave microscopy was used for mapping of the dielectric response of selected samples. The results show differences in the crystal structure between plasma sprayed coatings and feedstock powders in the case of BaTiO3 and MgTiO3 whereas CaTiO3 is crystalograffically identical with its feedstock. The reason can be found in larger sensitivity of BaTiO3 and MgTiO3 to the reductive conditions at plasma spraying whereas CaTiO3 seems to be rather inert from this viewpoint. However CaTiO3 exhibits anomalous dielectric losses because of intrinsic conductivity.