High-resolution electron microscopy for incommensurate structure of KxRhO2 crystal

摘要

An incommensurate, (3 + 2)-dimensional structure is locally observed in a K0.49RhO2 crystal synthesized by the flux growth method. The averaged potassium to rhodium ratio of the grown crystals was determined as 0.49 using an electron probe microanalyzer operated in the wave dispersive spectroscopy mode. The potassium content of the incommensurate phase was determined as 0.25 by the transmission electron microscopy-energy dispersive spectroscopy method. Satellite reflections of an incommensurate phase having two modulation vectors, q(1)* = 0.15a(o)* + 0.21b(o)* and q(2)* = -0.21a(o)* + 0.36b(o)* (a(o) is the unit cell for a gamma-NaxCoO2-type structure), are indexed successfully. High-resolution electron microscopy (HREM) images show dark streaks running parallel in the a-b plane. The separations and directions of the dark streaks have a close relationship between the q-vector of satellite spots. A HREM image taken with the electron beam parallel to 100 direction shows planer clusters between CdI2-type RhO2 layers. These clusters correspond to the intercalated potassium ions.