The 63 K phase transition of ZrTe sub 3 : a neutron diffraction study

The 63 K phase transition of ZrTe sub 3 has been followed through SQUID magnetisation and neutron diffraction studies. The transition is characterized by a small quenching of the magnetic susceptibility. Contrary to the expectation that the structural transition is associated with a charge density wave, the results of Rietveld refinements of high resolution neutron powder diffraction profiles indicate that below the phase transition the different bonding Te-Te contacts are more equal rather than less. The results are examined with the help of band structure calculations on structures determined at three different temperatures. The picture that emerges supports the view that anion-cation redox competition plays a crucial role in determining not only the structures of these compounds, but also the temperature dependence thereof.