Negative thermal expansion of ReO₃: Neutron diffraction experiments and dynamical lattice calculations

We have investigated the temperature variation of the unit-cell volume of ReO₃ by neutron diffraction. The lattice parameter and the unit-cell volume decrease continuously as the temperature is increased from T=2 K to about T=200 K. After exhibiting minima at about 200 K they increase with increasing temperature linearly up to about 305 K, the maximum temperature investigated during the present experiment. We attribute the negative thermal expansion of ReO₃ to be the results of rigid antiphase rotations of the neighboring ReO₆ octahedra. We have done model lattice dynamical calculation of phonon dispersions, thermal expansion, and atomic displacement parameters in ReO₃. The results of these calculations are in agreement with the experimental results.