Chloride Flux Growth of La2TiO5 Crystals and Nontopotactic Solid-State Transformation to LaTiO2N Crystals by Nitridation Using NH3

详细信息    查看全文

• 作者：Kenta Kawashima ; Mirabbos Hojamberdiev ; Hajime Wagata ; Kunio Yubuta ; Shuji Oishi ; Katsuya Teshima
• 刊名：Crystal Growth & Design
• 出版年：2015
• 出版时间：January 7, 2015
• 年：2015
• 卷：15
• 期：1
• 页码：333-339
• 全文大小：470K
• ISSN：1528-7505

文摘

Oxynitride perovskites and related phases have received considerable attention due to their potential application for visible-light-responsive photocatalyst and nontoxic inorganic pigments. The changes in bonding and structure by a partial replacement of O^{2鈥?/sup> by N3鈥?/sup> give rise to interesting dielectric behavior. Here, we report on the fabrication of highly crystalline La₂TiO₅ crystals by chloride flux growth method and their subsequent nitridation to form the LaTiO₂N crystals using NH₃ gas. The flux-grown La₂TiO₅ crystals had a columnar structure grown in the 鉄?01鉄?direction. Using the NaCl flux, larger columnar La₂TiO₅ crystals were grown compared to those grown using the KCl flux. With increasing solute concentration, the aspect ratio of columnar La₂TiO₅ crystals decreased significantly. The columnar La₂TiO₅ crystals with smooth surface were readily converted by nitridation at 950 掳C for 45 h followed by acid treatment into the LaTiO₂N crystals with a highly porous structure that formed from the strong segregation of nanocrystals, leading to the largest specific surface area (16.5鈥?8.4 m2路g鈥?). For the La₂TiO₅ crystals grown using the chloride fluxes, the wavelength of the absorption edges was approximately 320 nm (E_g = 3.87 eV), whereas the absorption edges exhibited by the LaTiO₂N crystals obtained by nitridation were approximately 600 nm (E_g = 2.06 eV). Particularly, the LaTiO₂N crystals prepared in this study by nitriding the precursor La₂TiO₅ crystals did not show a noticeable absorption in the near-infrared region above 600 nm, which is generally attributable to some reduced Ti3+ species and nitrogen deficiency, even after a long nitridation process. The fabricated LaTiO₂N crystals with low defect density will be advantageous for various applications that specially require higher specific surface area.}