Synchrotron X-ray study of charge density waves in o-TaS₃

We report a synchrotron X-ray study of charge density waves (CDW) in an o-TaS₃ crystal. CDW of o-TaS₃ has been known to undergo a commensurate-incommensurate transition at 100 K, below which the wavevector locks in with the pristine lattice. We exploited the beamline BL02B1 of SPring-8. Temperature dependence of the Bragg peak (002) and satellite peak (1 -1 2)+Q was measured from 7 K to 180 K. We found that a new phase in a temperature range of 130 - 50 K, where two independent CDWs coexist. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q _c=0.252c* and 0.250c*, respectively. By lowering the temperature, intensity of the incommensurate CDW was decreased, while that of the commensurate CDW was increased. At 50 K, the incommensurate CDW was completely diminished. Based on the concept of discommensuration, we determined the dislocation configuration from the intensity of the two CDWs.