Abstract
It is shown that slight decomposition of Nb 3O 7F occurs readily in the beam of an electron microscope. Planar faults are produced on at least five different ( hkl) planes. These grow into the crystal from the surface by expansion of partial dislocations. Further decomposition requires much higher beam heating and results in complete recrystallization and void formation giving a poorly ordered double-shear structure based on Nb 3O 7F. It is suggested that the first stage involves some reduction of Nb 5+ with release of oxygen and/or fluorine whereas the different mechanism of the second stage follows from the evolution of NbOF 3, a reaction which does not occur by a simple solid state mechanism.
Published Version
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