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 (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.