In mixed-anion systems, partial anion order can be the key to realizing enhanced dielectric properties. A novel A2B2X6X′0.5-type oxyfluoride pyrochlore, Pb2Ti2O5.4F1.2, was prepared through the conventional solid-state reaction. Characterization of the oxyfluoride pyrochlore by synchrotron X-ray diffraction and electron diffraction revealed the existence of partial O2-/F- order at the X site, in which F- is involved in fac-type Ti(O/F)6 coordination, associated with the O2-/vacancy order at the X′ site. Although Pb2Ti2O5.4F1.2 adopts a centrosymmetric structure, the refined occupancy factors suggested the existence of local polarization. Partial O2-/F- anion order stabilized the large displacement of Ti4+, leading to a high dielectric constant (as high as 800) with a low-temperature coefficient. These results suggest that mixing heteroanions in pyrochlores provides a basis for exploring novel dielectric materials.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Materials Chemistry