Polarization behavior of sol-gel-derived relaxor Ba(Zr, Ti)O3 films

Films of the relaxor ferroelectric BaZr0.25Ti0.75O3 (0.25-BZT) were synthesized via a sol-gel route to investigate the effect of film thickness on the dielectric properties and for comparison with normal ferroelectric BaTiO3 (BT). The as-prepared films on Nb-doped SrTiO3 (Nb-ST) displayed a (100) orientation; thinner films had stronger (100) orientations. Microwave dielectric measurements up to a few GHz quantified the polarizations, that is, the dipole contribution, epsilon(dipole), the combination of the ionic and electronic polarizations, epsilon(ionic+el.), and the total contribution, epsilon(total). The epsilon(dipole) in the relaxors at a film thickness of t=630nm was 360, which was double that for the normal ferroelectric BT (epsilon(dipole)=180) at t=735nm. The larger apparent permittivity of the BZT therefore originated from the larger epsilon(dipole) of the polar nanoregions (PNRs), while the nanograins of BT with few domain walls led to a comparably smaller epsilon(dipole). The volume ratio of the surface and film-substrate interface lacking the dipole interactions increased with the reduction in the film thickness, leading to the significant depression in the permittivity for both specimens. The difference in the thickness dependence of the dielectric properties of the sol-gel derived relaxor BZT and the normal ferroelectric BT films was attributed to the different origins of their dipole contribution, that is, the PNRs and ferroelectric domains, respectively.