Effects of Cr and Nb doping on the ferroelectricity of chemical-solution-deposited Bi3.5Nd0.5Ti3O12 films

The effects of Cr and Nb doping and annealing processing on the microstructure and ferroelectricity of Bi3.5Nd0.5Ti3O12 (BNT) films deposited by chemical-solution method were studied. The BNT films deposited from 0.05 M solutions showed larger grain size and thus better ferroelectricity than those deposited from 0.075 M solutions. For the Cr-doped BNT (BNTCx) films only Cr3+ substitutionally incorporated into the Ti4+ site of the TiO6 octahedron. Cr doping could result in the increase of the number of oxygen vacancies, reduction of the grain size, and enhancement of c-axis oriented growth, leading to the degradation of the remanent polarization (2Pr) of BNTCx films. For the Nb-doped BNT (BNTNx) films the 2Pr first increased from 40 μC/cm2 at x = 0-43 μC/cm2 at x = 0.005 and then decreased with increasing the Nb concentration (x) in the range of 0.01-0.1. The Nb cations substitutionally incorporated into the Ti4+ site of the BNT lattice were in the state of Nb5+, which could reduce the amount of oxygen vacancies and thus improve the 2Pr. The doping of Nb5+ into the BNT films could induce four effects on the 2Pr, i.e., reducing the amount of oxygen vacancies, reducing the grain size, enhancing the (1 0 0)/(0 1 0)-oriented growth, and possibly changing the lattice distortion of the TiO6 octahedron.