Nanoscale Dipole Engineering of BaTiO3 Using Y+3-Ta5+ Dipoles
Date
2021-05
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Abstract
Electric-field dipole engineering at the nanoscale (E-DENS) allows scientists and engineers to investigate and modify the electric-field interactions of atoms at the atomic level and determine how those interactions affect material properties. To further elucidate this construct, dipole pairs of Y5+-Ta5+ have been substituted for pairs of Ti4+ in barium titanate (BaTiO3), using the formula Ba[(Y3+,Ta5+)xTi1-2x]O3 with 0.0000≤x≤0.0500, to maintain charge neutrality. BaTiO3 is prominently used in the production of ceramic capacitors, due to its ability to store electrical charge in reduced size, volume, and weight. Since Y+5 and Ta+3 each are more polarizable than Ti4+ and since dipole formation of Y+5-Ta+3 pairs add additional energy into the lattice, the newly formed materials are anticipated to behave similar to previously reported E-DENS materials, where dipole pairs Ga3+-Ta5+, transformed BaTiO3 from ferroelectric to diffuse phase to relaxor-like material within a solid solution range Ba[(Ga3+,Ta5+)xTi1-2x]O3, 0.0000≤x≤0.05001. Compared with Ga3+, Y3+ is a cation that possesses higher polarizability (3.84 Å3 versus 1.50 Å3) and larger ionic radii (1.040 Å versus 0.76 Å) with radii no longer able to freely fit and move within the same octahedral cage in which Ti4+, Ga3+ and Ta5+ may “rattle”. Hence, although the dipole strength using Y3+ in place of Ga3+ with Ta5+ should be roughly the same, though slightly reduced due to separation distance from constraints of Y3+, use of Y3+, as indicated by the new simple material model including Clausius – Mossotti relation, is anticipated to increase Tm and Tc, while the dipole interaction is expected to result in roughly the same concentration dependent diffuseness (slightly less diffuseness due to anticipated slight decrease in dipole field strength). Further, due to the strength of the dipole field, the lattice parameter Ba[(Ga3+,Ta5+)xTi1-2x]O3 is expected to be larger and expand more quickly than Ba[(Y3+,Ta5+)xTi1-2x]O3. Room temperature x-ray diffraction was performed throughout the experiment to verify crystallinity and lattice parameters. UV-VIR-NIR data was collected to determine the energy bandgap of the doped materials to compare it to pure BaTiO3, along with temperature dependent resistivity to determine activation energy, and temperature dependent LCR analysis to determine relative permittivity, and dielectric loss of the substituted and parent materials.
Description
Thesis completed in partial fulfillment of the requirements for the Alfred University Honors Program.
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Thesis
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Keywords
Honors thesis, Ceramic engineering, Electroceramics, Barium titanate