Investigation of the structure of barium titanate thin films by Raman spectroscopy

Abstract

Raman spectroscopy was used to examine the structure of barium titanium oxide thin films grown by metal-organic chemical vapor deposition (MOCVD) and laser-assisted deposition. The spectra were compared with the spectra of a ceramic specimen and a single crystal. Raman peaks specific to the tetragonal ferroelectric phase of BaTiO3 were seen in the spectra of several films. Other Raman peaks were ascribed to impurity (non-BaTiO3) phases in the films or to the substrates (fused quartz, MgO). Some of the Raman peaks showed a strong polarization dependence. The MOCVD films were also characterized by x-ray diffraction, energy-dispersive x-ray spectroscopy, and transmission electron microscopy. The film-to-film variation of the strength of BaTiO3 features in the Raman spectrum, relative to impurity-phase features, was qualitatively consistent with the x-ray diffraction and electron microscopy results. Spatially resolved Raman measurements showed that the structure of the laser-deposited film varies significantly over the deposited area. The temperature dependencies of the Raman spectra of two MOCVD films were examined in the 25–175 °C range. Raman peaks due to the tetragonal phase of BaTiO3 were observed at temperatures well above the Curie temperature of bulk single-crystal BaTiO3 (132 °C). This observation suggests that the tetragonal ferroelectric phase is stabilized by an anisotropic film-substrate interaction that gives rise to a two-dimensional stress in the plane of the film.

Crystallization, phase evolution and ferroelectric properties of sol–gel-synthesized Ba(Ti0.8Zr0.2)O3–x(Ba0.7Ca0.3)TiO3thin films

“…The maximum polarization of BZT-0.50BCT thin lms may be due to a low energy barrier of the lm for polarization rotation and lattice distortion. 47 The coercive eld was dramatically higher than the value of 1.68 kV cm À1 for the bulk ceramic counterpart. 10 The much higher coercive eld came from the much smaller grains in comparison with the bulk ceramic and hence much more grain boundaries in thin lm samples, and also the substrate clamping effect.…”

“…For solution B, to suppress the hydrolysis of Ti(OC 4 H 9 ) 4 , an appropriate amount of glacial acetic acid was rst added to the accurately weighed Ti(OC 4 H 9 ) 4 , stirring for 20 min, followed by adding ZrO(NO 3 ) 2 $2H 2 O and absolute alcohol, and stirring at room temperature for 1 h to form Ti-Zr solution. Finally, solution A was added into solution B with stirring for 2.5 h at room temperature, and then maintained at [40][41][42][43][44][45][46][47][48][49][50] C for about 1 h to obtain a clear and homogeneous gel. Thin lms were prepared by spin-coating the above solution at 800 rpm for 9 s and at 3000 rpm for 30 s on clean platinumcoated silicon substrates.…”

“…35 The band at about 726 cm À1 has been observed in the tetragonal phase of BZT-0.5BCT and is related to the highest frequency longitudinal optical mode (LO) A1 symmetry and E (LO). [36][37][38] The peak at 305 cm À1 attributed to the B1 mode is a characteristic peak for BZT-0.5BCT and indicates the asymmetry of the TiO 6 octahedra. 39,40 This band is considered to be the Raman signature of the tetragonal phase.…”

Impact of layer defects in ferroelectric thin films

“…due to the presence of boundary surfaces, interfaces, impurities and other defects in the crystal. These localized modes appearing in the above mentioned structures are experimentally observed using the neutron and Raman scattering [16,17], or, more recently, far infrared absorption [18]. The Green's function theories have been extensively employed to describe these modes in semi-infinite transverse Ising models [19] and FE thin films [20].…”

Characterization of barium titanate nanoparticles and dense nanograin free-standing films via sol-gel method using highly concentrated alkoxide solution

“…21) Moreover, the other broad peaks around 180, 260, 520 and 720 cm ¹1 were consistent with coarse-grained tetragonal BaTiO 3 . 22) Hence, the symmetry of BaTiO 3 nanoparticles fired at 800°C or higher are considered to be tetragonal. In contrast, the symmetry of the samples fired at 600°C or lower was not clear due to suppression of the peak at 305 cm…”