PREPARATION OF PREFERENTIALLY ORIENTED BaTiO_3 THIN FILM BY HYDROTHERMAL SOFT CHEMICAL PROCESS

摘要

Epitaxial crystal growth technique is usually utilized to obtain preferentially oriented thin films of ceramics. In this technique, single crystal substrates are indispensable and lattice matching between the substrate crystal and the thin-film crystal is crucial, leading to high costs for the preparation of epitaxial thin films. In contrast, if polycrystalline or amorphous materials can be used as substrates, oriented thin films can be prepared on them at a low cost with a high degree of flexibility in their size and shape. In the present study, a hydrothermal soft chemical processing has been established as a method to prepare BaTiO_3 thin films with preferred orientation on a variety of substrates. A layered H~+-form titanate Hi_(1.07)Ti_(1.73)O_4·nH_2O (HTO) was prepared from a layered titanate of K_(0.8)Ti_(1.73)Li_(0.27)O_4·H_2O (KTLO) with a lepidocrocite-like layered structure and was used as a precursor. The HTO precursor powder was exfoliated into the nanosheets of elementary layer of its structure by reacting with a 0.1 M n-propylamne solution. A preferentially oriented HTO thin film was then prepared on the metal substrate of Ti, Pt, or Au by spin-coating with the HTO nanosheet colloidal solution, followed by heating at 200°-400℃. BaTiO_3 thin films with high [110] preferred orientation (Lotgering factor ≈ 1.0) were successfully prepared by hydrothermal treatment of the HTO precursor thin film in Ba(OH)_2 solutions at 150°-250℃. The direction of preferred orientation of the titanate thin film was dominated by the structure of the HTO precursor thin film and was not dependent on the properties of the substrate.