Chloride flux growth of La2TiO5 crystals and nontopotactic solid-state transformation to LaTiO2N crystals by nitridation using NH3

Kenta Kawashima, Mirabbos Hojamberdiev, Hajime Wagata, Kunio Yubuta, Shuji Oishi, Katsuya Teshima

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36 Citations (Scopus)

Abstract

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 O2- by N3- 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 〈001 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 °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 (16.5-18.4 m2·g-1). For the La2TiO5 crystals grown using the chloride fluxes, the wavelength of the absorption edges was approximately 320 nm (Eg = 3.87 eV), whereas the absorption edges exhibited by the LaTiO2N crystals obtained by nitridation were approximately 600 nm (Eg = 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.

Original languageEnglish
Pages (from-to)333-339
Number of pages7
JournalCrystal Growth and Design
Volume15
Issue number1
DOIs
Publication statusPublished - Jan 7 2015
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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