Determination of the deuterium position in DNb6I11

Abstract

Neutron diffraction data from a sample of composition D_0.45Nb₆I₁₁ were collected on a four-circle diffractometer at 120 K (low-temperature phase, P2₁cn) and 350 K (high-temperature phase, Pccn). According to Guinier X-ray diagrams, the investigated specimen prepared by heating a Nb₆I₁₁ crystal in D₂ consisted of epitaxially intergrown Nb₆I₁₁ and DNb₆I₁₁, i.e. the deuteriation reaction did not reach the inner part of the crystal. A ‘twin’ refinement (intensity coupling) was therefore performed. The D atoms occupy central positions in the Nb₆ cage both at high and low temperature. The thermal ellipsoids of the D atoms exclude a time-averaged off-centre position.