Doping Mechanism and Permittivity Correlations in Nd-Doped BaTiO3

BaTiO₃ forms an extensive range of solid solutions with Nd₂O₃ by means of the double substitution mechanism: Ba + Ti 2Nd, as shown by both a phase diagram study and Rietveld refinement using powder neutron diffraction data. The solid solutions have the general formula Ba_1-xTi_1-xNd_2xO₃Odxd0.12 at 1300°C and 1300°C and O dxd at 1400°C. With increasing x, the symmetry changes from tetragonal to cubic at x 0.09. The sharp permittivity maximum at 127°C in stoichiometric BaTiO₃ broadens very rapidly with increasing x and gradually moves to lower temperatures: this appears to be because, with substitution of Nd onto Ti sites, formation of the ferroelectric domains is increasingly difficult because of the presence of dipole-inactive Nd³⁺ ions on the Ti sites.