Dielectric properties of plasma sprayed titanates

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((R)) as well as commercial A-PS (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. (C) 2001 Elsevier Science Ltd. All rights reserved.