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High Resolution Electron Microscopy of Triply Incommensurate Phase of 2H-TaSe2

Published online by Cambridge University Press:  25 February 2011

Takashi Onozuka
Affiliation:
School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907
Nobuo Otsuka
Affiliation:
School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907
Hiroshi Sato
Affiliation:
School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907
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Abstract

The triply incommensurate phase of 2H-TaSe2 obtained by cooling from the normal phase was investigated by TEM between 87K and 113K with the resolution of 3 A. Moire-like patterns observed in this phase were confirmed to be interference fringes due to the first and the second order diffraction beams from the incommensurate structure and were not due to the dark field diffraction contrast of domains of the commensurate structure as interpreted earlier. Lattice fringes (∼9Å) of this modulated phase do not show any discontinuity across the boundaries of regions of different contrasts of the moire-like fringes which is expected from domain boundaries. Instead, a periodic change in the spacing of the lattice fringes (phase slip region) expected from the superposition of split superlattice spots in forming the lattice image is observed. This is the first direct observation of the existence of the phase slip region which is also expected from the discommensuration theory.

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Articles
Copyright
Copyright © Materials Research Society 1986

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