Spontaneous polarization change with Zr/(Zr plus Ti) ratios in perfectly polar-axis-orientated epitaxial tetragonal Pb(Zr,Ti)O3 films

Epitaxial Pb(Zr,Ti)O-3 (PZT) films 50 and 250 nm thick with the Zr/(Zr+Ti) ratio from 0.13 to 0.65 were grown on (100)(c)SrRuO3//(100)SrTiO3 substrates at 540 degreesC by pulsed-metalorganic chemical vapor deposition. The crystal orientation, lattice parameter, axial angle, and relative volume fraction of constituent domains were determined by high-resolution x-ray diffraction reciprocal space mapping. We grew (100) and/or (001)-oriented epitaxial PZT films for the whole Zr/(Zr+Ti) ratio. A tetragonal single phase was obtained for the Zr/(Zr+Ti) ratio ranging from 0.13 to 0.54 and 0.19 to 0.45 with the 50 and 250 nm thick films, respectively, while mixed phases of a tetragonal and rhombohedral from 0.45 to 0.60 for the 250 nm thick films was obtained. For the films consisting of a tetragonal single phase, lattice parameters of a- and c-axes and their ratio (c/a) were almost the same as the reported data for the PZT powder, suggesting a small amount of residual strain in them. In addition, perfectly polar-axis (c-axis)-oriented tetragonal films were obtained for the 50 nm thick films, while an similar to70% c-axis-orientation for the 250 nm thick ones was obtained. Polarization-electric-field hysteresis loops with a good square shape were observed for all films. Also, spontaneous polarization (P-s) values that were directly measured for the 50 nm thick films and estimated for the 250 nm thick films taking into account the volume fraction of the polar-axis-orientated domain were closely in line with the Zr/(Zr+Ti) ratio, and they decreased as the ratio increased. The square of the estimated P-s was found to be proportional to the crystal distortion, c/a-1. These results are essential not only for understanding the origin of the large P-s of PZT but for the property design of the ferroelectric devices using PZT. (C) 2004 American Institute of Physics.