Inducing Diffuse Phase Transitions in Barium Titanate Using Ga3+-Ta5+ Dipole Pair Substituents

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New York State College of Ceramics at Alfred University. Inamori School of Engineering.
Ba{[Gax,Tax]Ti(1-2x)}O3 with x equal to 0, 0.0025, 0.005, 0.01, 0.025 and 0.05 have been prepared by conventional solid-state reaction and sintered to greater than 95% density. Structural and dielectric characterization have been performed to investigate the effect of dipole-pair concentration on the properties. Dielectrically, the Ba{[Gax,Tax]Ti(1-2x)}O3 phase transition evolves from a classic ferroelectric to a diffuse phase transition (DPTs) as x increases. Ba{[Gax,Tax]Ti(1-2x)}O3 for 𝑥≥0.01 possesses diffuseness parameters comparable to Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), yet it lacks the frequency and temperature dependence of Tm necessary to be a strictly defined relaxor ferroelectric. Additionally, Ba{[Ga0.05, Ta0.05]Ti0.9}O3 possesses a relative permittivity, εr, of 700±16% and dissipation factor less than 0.05 at 10 kHz within the temperature range [-75°C, 120°C]. In comparison to BaTiO3, Ba{[Gax,Tax]Ti(1-2x)}O3 possesses enhanced electrical resistivity and greater time constant at and above room temperature. Through varying the concentration of dipole-like substitutions, material evolution of properties could be systematically investigated and material properties like resistivity, RC time constant, breakdown strength, maximum εr, temperature sensitivity of εr, dissipation factor, etc. can be individually optimized or any combination(s) of material properties can be optimized to achieve desired device or system performance. The relaxation of εr is found to increase linearly with the dipole concentration. In-situ XRD, including Rietveld refinement, have been performed to determine the lattice parameter, coefficient of thermal expansion and phase transition temperature of each composition within the temperature range [RT, 1000°C]. The unusual properties of Ba{[Gax,Tax]Ti(1-2x)}O3 are discussed in context with available models describing donor and acceptor dopants spatially separated in the parent matrix that inter-relate lattice parameter, Curie temperature, and other material properties.
Dissertation completed in partial fulfillment of the requirements for the degree of Masters in Science in Ceramic Engineering at the Inamori School of Engineering, New York State College of Ceramics at Alfred University