Influence of Solvents on the Microstructure and Dielectric Properties of Ba_0.5Sr_0.5TiO₃ Thin Films Prepared by a Diol-Based Sol−Gel Process

Abstract

Ba x Sr1 - x TiO3 (BST, x = 0.5) thin films were prepared on Pt/TiO2/SiO2/Si substrates using a diol-based sol−gel method. Two different solvents were employed, ethylene glycol and propylene glycol (1,2-propanediol). The influence of the solvent on the sol structure, microstructure development, and dielectric properties of BST thin films is analyzed and discussed. It is observed that films prepared with ethylene glycol show higher values of the dielectric permittivity (∼40% higher) and lower values of dielectric losses when compared with films prepared from propylene glycol precursors. The dielectric permittivitty is 459 and 302 at 1 kHz for films prepared with ethylene glycol and 1,2-propanediol, respectively, and annealed at 800 °C. IR studies revealed that the stabilization of a titanium precursor with propylene glycol is incomplete. During the phase-formation process, a higher content of a second phase is formed for the propylene glycol-delivered films. However, microstructure analyses revealed smaller grain size and surface roughness and higher density for films prepared with ethylene glycol. These differences are attributed to the relative high boiling point and latent heat of vaporization and to the linear molecular structure of ethylene glycol. Ethylene glycol as a solvent allows for the preparation of BST thin films with improved dielectric properties.

Low-temperature synthesis of BiFeO3 nanopowders via a sol–gel method

“…SrBi 2 Ta 2 O 9 [17] and Ba 0.5 Sr 0.5 TiO 3 [14]) because the presence of two terminal hydroxyl groups in the molecule makes it easy for ethylene glycol to readily keep heterometallic units during hydrolysis reaction. It is reported that the linearly structured molecule of ethylene glycol is favorable for obtaining stable sol and acts as the template for a dense and linearly aligned structure of the precursor molecules [14]. The decomposition products between 200 and 300 • C are mainly linear organic molecules.…”

“…The linear organics are originated from decomposition of the linearly structured gel network. The linearly structured molecule of ethylene glycol will easily react with the nitrates to form a stable precursor molecule and will also act as the template for a dense and linearly aligned structure of the precursor molecules [14]. Based on a micromechanism for crystallization of amorphous alloys proposed by Lu and Wang [18], a micromechanism for crystallization of BFO gels is proposed.…”

“…3 shows the infrared spectra of thermal-treated powders. The broad band between 3500 and 3000 cm −1 was attributed to O-H stretching [13] originated from ethylene glycol or condensation products, which decreased in intensity as thermal-treatment temperature increased, but persisted to around 300 • C. The bands in the frequency range 1600-1400 cm −1 were assigned to the asymmetric and symmetric COO − stretching vibrations of the acetate ligands [14]. The bands around 1655 and 1300 cm −1 possibly correspond to the formation of esters during the condensation reaction between ethylene glycol and acetic acid in the sol-formation process.…”

Dielectric Properties of Sol–Gel‐Derived Bi12SiO20 Thin Films

“…However, the dielectric/insulator properties are not stand‐alone device requirements. It is well documented that the variations in the dielectric properties of the thin films are strongly influenced by the sample composition, crystallinity, and morphology of the films . Therefore, part of our investigation was also focused on the above‐mentioned thin‐film parameters to ensure optimum and reliable dielectric properties.…”

“…It is well documented that the variations in the dielectric properties of the thin films are strongly influenced by the sample composition, crystallinity, and morphology of the films. [14][15][16] Therefore, part of our investigation was also focused on the above-mentioned thin-film parameters to ensure optimum and reliable dielectric properties. Figure 3 shows the XRD patterns of the BSO thin films deposited on the Pt/TiO 2 /SiO 2 /Si [ Fig.…”