Recently, an attraction to pyrochlore oxides has grown significantly due to a wide range of physical properties, such as magnetism and nuclear waste disposal. An area of research on this class of materials stems from pyrochlores that exhibit ferroelectric behavior.1 A subset of piezoelectricity, materials which are ferroelectric exhibit spontaneous polarization which can be reversed with an applied electric field2. Interest pertaining to a material’s polarization has occupied a place in current science with various types of applications ranging from sensors, motors, and capacitors. Typically pyrochlore materials (A2B2O7) tend to exhibit geometrical frustration of dipoles due to the triangular arrangement of cations,2 which prevents the formation of a ferroelectric structure. However, some pyrochlores exhibit ferroelectric behavior despite this geometric consideration, and the origin of such is an area of interest. An example of a frustrated pyrochlore is Bi2Ti2O7, which contains stereochemically active lone pair electrons on the Bi3+ cation1 that lead to random distortions through Bi3+ off-centering. Herein we attempt to relieve this frustration through partial substitution of Bi3+ with rare earth metals (Ho), which do not have a lone pair of electrons and should not off-center from their ideal site. We will present both solid state and solution-based synthesis routes and the structural effects regarding the substitution of Ho at various concentrations. The formula Bi2-xHoxTi2O7 allowed for fully substituted pyrochlores to be incrementally observed as new elements were introduced. The average structure and morphology of all samples have been characterized using X-ray diffraction and Scanning Electron Microscopy, respectively. Analysis of Bi2-x HoxTi2O7 revealed that the pyrochlore phase forms closer to the Ho2Ti2O7 end member through solid state routes. Additionally, we were able to realize formation of the Bi2Ti2O7 end member using hydrothermal synthesis. SEM indicates difference in morphology based on synthesis route. The ultimate goal of this study is to understand the origins of long-range order in pyrochlores to rationally design new polar pyrochlores for electronic applications.

Synthesis and characterization of Ho-substituted bismuth pyrochlores

2019 Spring National Meeting

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