Synchrotron radiation X-ray diffraction of modulated structures in charge-density-wave materials. Application to NbSe3

Abstract

Synchrotron radiation X-ray diffraction has been performed on niobium triselenide at 20K. The modulation parameters belonging to both Charge-Density-Waves (CDW's) have been determined. The high-temperature CDW is found to comprise of displacements on all atoms of column III, as well as on Se atoms of column II. Similarly, the low-temperature CDW resides on column I and also involves displacements of some Se(II). The structure is interpreted in terms of CDW's on Nb(III) and Nb(I), and elastic coupling between the atoms. The correlations between the atomic displacements are studied by analyzing the correlations between the varying interatomic distances. The atomic valences are discussed in the framework of the Bond-Valence method.