The influence of nonstoichiometry on the Verwey transition in magnetite as studied by Moessbauer spectroscopy
Abstract
Moessbauer spectroscopy was employed to investigate the influence of the extent of deviation from ideal stoichiometry on the order of the Verwey transition in magnetite. The Moessbauer absorbers were prepared under a Helium atmosphere at room temperature; the powdered magnetite single crystals used for this purpose were grown in a skull melter and then annealed under a controlled oxygen atmosphere to produce homogeneous, single phase specimens. For absorbers prepared with $\delta\leq$ 0.0035, a sharp first order transition was observed. For samples produced with $\delta\geq$ 0.0060, a gradual change in the temperature dependence of the Moessbauer interactions, indicating a second or higher order transition, was seen. The first experimental evidence for a second octahedral site for all samples above their respective Verwey transition temperatures was found. An interpretation of the temperature dependence of three major Moessbauer interactions, (the magnetic hyperfine splitting, the quadrupole splitting, and the isomer shift), was given in terms of the mean-field theoretic approach to phase transitions.
Degree
Ph.D.
Advisors
Honig, Purdue University.
Subject Area
Chemistry
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