Observation of local atomic displacements intrinsic to the double zigzag chain structure of 1T−MTe2 ( M=V, Nb, Ta )

Abstract

We describe the existence of local distortion discovered in the synchrotron x-ray single-crystal structure analysis of layered ditelluride $1T\text{\ensuremath{-}}M{\mathrm{Te}}_{2} (M=\mathrm{V}$, Nb, Ta). In $1T\text{\ensuremath{-}}{\mathrm{TaTe}}_{2}$, the double zigzag chain structure of Ta is deformed at about 170 K, and heptamer molecules are formed periodically at low temperatures. We found that some of the Ta atoms that compose the double zigzag chain structure appearing at high temperatures are locally displaced, resulting in local dimerization. This tendency weakens when Ta is replaced by V or Nb. Our results indicate that the local distortion persistently survives in these ditellurides, where the electronic degrees of freedom, including orbitals, are weakened. We further discuss the origin of local distortion in these ditellurides, which is different from many usual material systems where molecular formation occurs at low temperatures.