Epitaxial films were prepared by metalorganic chemical-vapor deposition onto (001)MgO, (001)SrTiO3 or (001)LaAlO3 substrates, and 4-circle X-ray diffraction, transmission electron microscopy, Rutherford back-scattering channelling and optical waveguiding were used to characterize them. Epitaxial monocrystalline films were obtained on all 3 substrates, under the same growth conditions. However, the defect structures (grain tilting, threading dislocation density, 90 domain formation) depended strongly upon the choice of substrate. Films which were grown onto (001)MgO and (001)LaAlO3 pseudo-cubic substrates were nominally c-axis oriented. However, the PbTiO3 grains in the film formed a 4-fold domain structure; with the grains tilted by about 0.6 and 0.7, respectively, towards the cubic or pseudo-cubic [100] directions of the substrates. In addition, these films contained a large volume fraction of 90 domain (a-axis) structures with a critical thickness (10nm) for domain formation which was below the detection level of the present experiments. These structural defects resulted in a low Rutherford back-scattering channelling yield reduction. On the other hand, films which were grown on (001)SrTiO3 substrates exhibited no tilting of the c-axis grains and a minimum Rutherford back-scattering channelling yield of as little as 3%. It was also observed that, below a critical film thickness of 150nm, 90 domain formation was completely suppressed. This resulted in an almost perfect monocrystalline structure. The refractive index and optical birefringence of the films were measured as a function of wavelength. It was found that the ordinary and extraordinary refractive indices of films which were grown on (001)MgO and (001)LaAlO3 were higher than those of monocrystalline PbTiO3. However, the optical birefringence of films which were grown on (001)MgO was lower from that of the bulk. In the case of films which were grown on (001)SrTiO3, the ordinary refractive index was very close to that of monocrystalline PbTiO3. The refractive index values and the reduced birefringence were related to the degree of residual strain, and to the volume fraction of 90 domains, respectively.

C.M.Foster, Z.Li, M.Buckett, D.Miller, P.M.Baldo, L.E.Rehn, G.R.Bai, D.Guo, H.You, K.L.Merkle: Journal of Applied Physics, 1995, 78[4], 2607-22