Observation of a novel phase transition in Sr7Re4O19

We have synthesized good-quality powder samples of Sr7Re4O19 and found a phase transition at 206 K accompanied by some changes in both electronic properties and structure. The values and the temperature dependence of magnetic susceptibility indicate the existence of a Pauli paramagnetic state above 206 K and a nonmagnetic state below 206 K. The electrical resistivity of the sintered sample gradually increases with decreasing temperature below room temperature and sharply increases below 206 K, which is followed by insulating behavior below 160 K. In addition, the structure changes from monoclinic to triclinic at the transition. Sr7Re4O19 has a quasi-one-dimensional structure comprising the coupled zigzag chain formed by corner-shared ReO6 octahedra. Further, a long=short alternation of the Re–Re distance along the zigzag chain is observed in the low-temperature phase. Quasi-one-dimensional Fermi surfaces and band dispersions are also identified by the electronic structure calculations. These results suggest that the phase transition is a possible metal–insulator transition caused by the Peierls instability.