Ferroelectricity in thin films: The dielectric response of fiber-textured (BaxSr1−x)Ti1+yO3+z thin films grown by chemical vapor deposition

We have investigated the dielectric response of a series of {100} fiber-textured $({\mathrm{Ba}}_x{\mathrm{Sr}}_{\text{1−x}}){\mathrm{Ti}}_{\text{1+y}}{\mathrm{O}}_{\text{3+z}}$ samples deposited by liquid-source metalorganic chemical vapor deposition onto ${\mathrm{Pt/SiO}}_{\mathrm{2}}\mathrm{/Si},$ as a function of the two most commonly varied microstructural parameters: film thickness and Ti nonstoichiometry y. We find that the overall behavior of these samples is adequately described by mean-field, Landau–Ginzburg–Devonshire theory as for bulk ferroelectrics. However, we quantify the impact of three separable factors for these films that greatly alter the dielectric susceptibility as a function of temperature, compared to that found for bulk ceramic samples at the same Ba/Sr ratio of 70/30: (i) Ti nonstoichiometry; (ii) the apparent interface effect; and (iii) the plane equibiaxial stress state resulting from thermal expansion mismatch strains. When these factors are properly taken into consideration, we show that these fine grained thin films behave in a manner entirely consistent with expectations based on bulk behavior. Implications can therefore be drawn concerning the nature of size effects in this ferroelectric system.