Investigations of a Novel Manganite Oxyfluoride and Other Ceramic Materials

Perovskite-type compounds are among the most important of inorganic solid-state materials, and exist in a wide variety of compositions with related crystal structures. These variations allow perovskite-type materials to display many important and useful properties, such as superconductivity, dielectrics, and colossal magnetoresistance. A primary goal of this thesis is to prepare an oxyfluoride analog of (Ca, La)MnO₃, known for its colossal magnetoresistive properties, and determine the effect of anion substitution on the magnetic properties of this material. The novel compound targeted for synthesis in this study is Ca₂Mn₂O₅F, which achieves a mixed Mn⁺³/Mn⁺⁴ oxidation in the lattice via anion rather than cation substitution, as is the usual case. This mixed oxidation is an important feature of manganite oxides displaying colossal magnetoresistance. A four-step process was proposed in order to synthesize the target oxyfluoride compound, and will be described in detail. While the first step was successfully completed, subsequent steps were not. These attempts will be summarized along with the conclusions from this study and suggestions for future work.

A second project discussed in this thesis is the Research Experiences to Enhance Learning (REEL) project, based on a state-wide initiative centered at the Ohio State University to introduce meaningful research experiences into the first and second year chemistry curriculum The YSU-developed REEL modules focus on perovskite-type compounds, and specifically for this study on solid solutions of KCuF₃ with KNiF₃ and KMnF₃. Thus the focus of the work was on the two series of compositions, K(Cu_xNi_1-x)F₃ and K(Cu_xMn_1-x)F₃ for x = 0, 0.1, 0.2 …0.9, 1.0. These two sets of compounds were prepared by students enrolled in the second semester general chemistry laboratory course during the Spring 2010 and Fall 2010 semesters. Students analyzed their compounds using X-ray Powder Diffraction (XRPD), UV-Vis Spectrometry, and X-ray Fluorescence (XRF) techniques under the guidance of this thesis author. The final data was then further analyzed and quantitatively refined in this study using Rietveld powder refinement methods. From the results, the solubilities of the cubic KNiF₃ and KMnF₃ phases in tetragonal KCuF₃ were determined, and compared to results of previous studies on the K(Cu_xCo_1-x)F₃ and K(Cu_xMg_1-x)F₃ systems.