Single crystals of Nd-substituted Bi4Ti3O12 ferroelectrics were grown by a self-flux method, and the effects of Nd substitution on the polarization properties and optical transmission spectra of the crystals have been investigated. B3.52Nd0.48Ti3O12 crystals showed a smaller remanent polarization along the a axis of 29 mu V/cm(2) than B4Ti3O12 crystals (46 mu C/cm(2)), and this result is in good qualitative agreement with the calculation of the spontaneous polarization based on Rietveld analysis of neutron diffraction. Electronic band structure calculations using the structural data suggest that the orbital hybridization between the Nd 5d and O 2p states stabilizes oxide ions in the perovskite layers, which is consistent with the much smaller leakage current observed for Nd-substituted crystals. (c) 2005 Elsevier Ltd. All rights reserved.