Electron Microscopy Study of the Charge-Density-Wave Transition in 2H-TaSe₂

The triply incommensurate phase in 2H-TaSe₂, which exists between 112 and about 85 K on cooling, has been investigated by means of electron microscopy. The high resolution micrographs clearly show that the incommensurate phase between 112 and 92 K is an intrinsic incommensurate phase without orthorhombic domains of the commensurate phase. On the other hand, the phase between 92 and about 85 K is a kind of the transition state to the commensurate phase. When the temperature is lowered, the orthorhombic domains nucleate along the discommensurations around 92 K and then the lock-in transition proceeds from the formation of the stripples consisting of one kind of the orthorhombic domains and their shrinking motion. These experimental results can be explained on the basis of the Ginzburg-Landau theory.