Diffuse Phase Transition in Epitaxial BaTiO3 Thin Films

Abstract

The thickness dependence of the dielectric properties of epitaxial BaTiO3 thin films was investigated for thicknesses ranging from 15 to 320 nm. The films were deposited by low-pressure metalorganic chemical vapor deposition on (100) MgO substrates. The relative dielectric permittivity and the loss tangent values decreased with decreasing thickness. High-temperature dielectric measurements showed that with decreasing film thickness, the ferroelectric-to-paraelectric transition temperature decreased, the relative dielectric permittivity decreased, and the phase transition was diffuse. The c/a ratio also decreased with decreasing film thickness. The observed behavior for epitaxial films of BaTiO3 was attributed to the presence of strain in the films.

Epitaxial Integration of Ferroelectric BaTiO3 with Semiconductor Si: From a Structure- Property Correlation Point of View

“…As the sputtering is proceed in an oxygen deficient atmosphere, thus the oxygen vacancies induced structural disorders and compositional fluctuations in the film may be responsible for the observed relaxor behavior. Similar diffusive transition had also been observed in BTO films on MgO and Pt-coated Si substrates [94,95].…”

Three Dimensional Domain Structure in Epitaxial Barium Titanate Thin Films

“…The large domain gradient for relatively modest strains is due to the weak tetragonality of BaTiO 3 . The strain/domain gradient through the film thickness could help explain the broad phase transitions and relaxor-like behavior often observed in epitaxial thin films [3].…”

“…For example, Gopalan and Raj [2] have demonstrated that the measured second-harmonic generation coefficient depended on the volume fraction of each domain type. The strain state of the film can also affect the Curie transition temperature and induce relaxor-type behavior [3]. Furthermore, Hoerman et al [4] have shown that the dynamics of the electro-optic response in polydomain films are dependent on domain structure.…”

“…These structures vary through the film thickness due to interface effects, dipole-dipole interactions and electrical boundary conditions [9]. Additionally, heteroepitaxial films exhibit strain relaxation away from the film/substrate interface, resulting in a strain gradient [3].…”

( Pb , Ca ) Ti O 3 ∕ ( Pb , La ) Ti O 3 ∕ ( Pb , Ca ) Ti O 3

“…5, together with the experimental data. It has to be noted that the calculated values along the whole range 32 an increase of permittivity with the thickness of the film has been observed in the whole range of temperature. Such an increase has been related to a stress relaxation as the film became thicker.…”