Structural and electronic properties of pyrochlore-type A ₂Re₂O₇ (A=Ca, Cd, and Pb)

Cd₂Re₂O₇ exhibits a unique structural transition characterized by a loss of the inversion symmetry in a metal. Here, we report on structural and electronic properties for A₂Re ₂O₇ (A=Ca and Pb), and S-substituted Cd₂Re ₂O₇. On the basis of material characteristics, we show that the covalency of particular bonds stabilizes the low-temperature phase without the inversion symmetry. We also observed an incoherent charge transport with a weakly temperature-dependent resistivity on the verge of structural transition. This phenomenon is argued in terms of the polaron formation.