Disorder-insensitivity of room-temperature giant permittivity in Ca4 − xCuxTi4O12 (x = 3, 2 and 1) polycrystalline ceramics

When the stoichiometric proportion of Cu in Ca4 − xCuxTi4O12 polycrystalline ceramics is decreased from 3 to 2 and then to 1, the room-temperature permittivity is reduced by one order of magnitude during each step. Ca/Cu atomic disorder is observed only in some grains of Ca3CuTi4O12 single-phase polycrystalline ceramics, and the disorder is not the origin of the giant permittivity in CaCu3Ti4O12. Quantitatively, the permittivity magnitude is related to the mole ratio of polaronlike 3d electrons from Cu ions.