Room temperature ferroelectricity in donor-acceptor co-doped TiO2 ceramics using doping-engineering

Conventional ferroelectric oxides are of generally non-centrosymmetric crystals resulting from paraelectric-ferroelectric transitions. Here, we present a new donor-acceptor ion co-doping route to room-temperature ferroelectricity in rutile TiO 2 , where ionic pair of co-doping ions plays very important roles in generating local broken symmetry and polarization. The (Nb + Al) co-doped TiO 2 sintered with a two-step method exhibits ferroelectricity and piezoelectric response, and it is believed that Nb 5+ -Al 3+ pairs along TiO 2 [001] direction play important role in the ferroelectricity. A large lattice distortion can be induced in the vicinity of the ionic pair, which results in local broken-symmetry. The relative displacements of cations and anions around the ionic pair, induced by the lattice distortion, cause the local polarization. The results and mechanisms presented in this work provide a new approach to the design of new ferroelectrics via doping engineering.