HIGH 'K' DIELECTRIC MATERIALS FROM METALLO-ORGANIC PRECURSORS (KINETICS, GRAIN, NEODYMIA, ULTRA-FINE, BARIUM-TITANATE, LEAD-TITANATE)
Abstract
The goal of these studies was to evaluate the metallo-organic technology as applied to dielectrics. As part of evaluation kinetics of compound formation, solid solution formation and dielectric properties of ultrafine grained materials were studied. Kinetics of BaTiO(,3) and PbTiO(,3) formation from metallo-organic precursors were studied. The fine grain size of the decomposed product and the greater degree of mixing led to very rapid kinetics of compound formation. The kinetics data were fit to the Carter model for a diffusion controlled process. Formation of PbTiO(,3) was modeled as a two stage process with a single activation energy, and the formation of BaTiO(,3) as a single stage process. Dielectric constant and spontaneous polarization of fine grain BaTiO(,3) prepared using metallo-organic decomposition (MOD) technology were studied. Room temperature dielectric constant of BaTiO(,3) increases sharply with increase in grain size, it reaches maxima at about 0.4 (mu)m and decreases with further increase in grain size. Spontaneous polarization continuously decreases with decrease in grain size. A model was proposed to explain the grain size dependence of dielectric constant. The defect structure and dielectric properties of BaTiO(,3) with 1-10 mole% Nd(,2)O(,3) additions were studied. The results indicated that neodymium occupies the barium site and charge compensation takes place by creation of titanium vacancies. The dependence of inverse electric susceptibility, spontaneous polarization and specific heat on temperature for samples containing more than 2 mole% of Nd(,2)O(,3) were characteristic of a diffuse transformation resulting from a disordering of defects. The addition of Nd(,2)O(,3) leads to a very drastic shift in the Curie temperature (T(,c)) of BaTiO(,3); 3 mole% Nd(,2)O(,3) addition moves T(,c) below room temperature.
Degree
Ph.D.
Subject Area
Materials science
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