Measurement of dielectric constant of BaTiO₃ powders by impedance spectroscopy

The objective of this thesis is to contribute to the reliable measurement of the dielectric constant of particulate materials by applying impedance spectroscopy techniques to slurries. Slurries were prepared by dispersing dielectric powders, such as BaTiCb in appropriate host liquids. The impedance spectrum of the slurry consists of two frequency dependent semicircles: Maxwell relaxation in the host liquid is responsible for the high frequency semicircle, whereas low frequency relaxation is due to the dispersed powder. This finding was confirmed by measuring slurries prepared using different powders and host liquids, as well as by variation of slurry solids loadings. Experimental modeling studies were also conducted. Model samples in form of cubes were prepared; different volume fractions were placed in the sample holder with the liquid to conduct impedance spectroscopy measurements. The same powder was used for preparation of slurries as well as bulk BaTi03. The dielectric constant values of powders determined by using slurries and model samples were consistent suggesting the validity of the technique for characterization of particulate materials. The effect of heat treatment conditions on the dielectric constant of hydrothermally prepared barium titanate was also studied. A significant change in dielectric constant of hydrothermal sub micrometer sized powders was found (for initial powder K: -600) and as annealing temperature exceeded 1000°C dielectric constant was found to be \u3e900. For micrometer (1pm) sized, tetragonal BaTiCE powder annealing temperatures up to 1200°C did not have any significant effect on the dielectric constant (K: 1500). Electrical measurements were confirmed with microstructure studies using SEM and XRD --Abstract, page iv