Evidence of structural phase transitions in superconductingRbxWO3

In the hexagonal tungsten bronze ${\mathrm{Rb}}_x\mathrm{W}{\mathrm{O}}_3$, the ordering of the vacancies of the Rb sites has been observed by neutron diffraction measurements. This ordering is the cause of the resistivity anomaly observed by Stanley et al. Another type of structural transition has also been found for the samples with $x<\mathrm{}0.25\mathrm{}$. The results give support to the speculated correlation between the superconducting transition temperature and a structural phase transition.