Graduate Thesis Or Dissertation
 

Designing Dielectric Materials through Complex Metal Oxides

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  • This dissertation demonstrated that the electrical properties of complex oxide-based perovskite materials could be controlled through the careful modification of both material composition and structure. This was first shown through the modification of lead zirconate titanate (Pb(Zr0.52Ti0.48)O3, PZT) solid solutions with bismuth indate (BiInO3, BI) where the relative stability of the parent PZT phases, tetragonal (P4mm) and rhombohedral (R3m,) were shifted with increasing additions of BI. There were also observations of a correlated reduction in the Curie temperature with increasing additions of BI. Control over the electrical properties was also demonstrated through the modification of the Ba0.85Ca0.15(Zr0.10Ti0.90)O3 solid solution with Bi(Zn0.50Ti0.50)O3 through the disruption of long-range ferroelectric dipole order, resulting in a relaxor ferroelectric phase with a very high permittivity over a very large temperature range. Studies into BI modified PZT solid solutions showed the formation of stable solid solutions with the incorporation of BI at up to 10 mol% for PZT compositions with a Zr:Ti ratio of 50:50, and with up to 15 mol% BI with a Zr:Ti ratio of 52:48. Dielectric and ferroelectric studies were carried out on xBI – (1-x) PZT (52/48) samples for 0% ≤ x ≤ 10%. These studies showed a decrease to the Curie temperature from 390°C at 0% BI to 325°C at 10% BI, a transition in the room temperature ferroelectric phase from tetragonal at 0%, to mixed tetragonal and rhombohedral at 2.5%, to rhombohedral at 5% and above, and a variation to the high temperature phase transitions prior to the cubic paraelectric phase resulting in a rhombohedral to tetragonal phase transition in the 10% BI composition. Ferroelectric studies showed all samples to saturate at approximately 40 kV/cm upon which polarization loops of a normal ferroelectric were observed with coercive fields ranging from 10.8 kV/cm to 14.1 kV/cm, remanent polarizations ranging from 7.4 C/cm2 to 12.1 C/cm2, and maximum polarizations ranging from 18.4 C/cm2 to 24 C/cm2 (properties summarized from a maximum applied field of 50 kV/cm.) Piezoelectric studies were carried out on 2.5% BI – PZT (52/48) samples showing an average maximum strain of 0.2% correlating to an inverse piezoelectric coefficient (d33*) of 280 pC/N at 70 kV/cm. The modification of the ferroelectric Ba0.85Ca0.15(Zr0.10Ti0.90)O3 solid solutions with 1% Bi(Zn0.50Ti0.50)O3 resulted in a high permittivity relaxor ferroelectric phase. The induced relaxor phase was observed to be very sensitive to both processing effects and stoichiometry, with small modifications to processing parameters resulting in complex changes to the magnitude of the permittivity and the size distribution of PNRs, as evidenced by shifts in the observed Tmax. The desirable high permittivity relaxor phase was determined to be dependent on the existence of secondary phases, as single-phase samples were observed to maintain relaxor character in the dielectric properties while exhibiting relatively low permittivity. The existence of secondary phases was determined to be a function of cooling rate, with increased cooling rates showing lesser impurities, and bismuth oxide excess, as opposed to being determined by maximum sintering temperature. This material was found to be promising for multi-layer ceramic capacitor applications, though further research is needed into mitigating space charge contributions to the permittivity.
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  • Intellectual Property (patent, etc.)
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  • 2020-12-23 to 2023-01-24

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