Ammonothermal Synthesis of Novel Nitrides: Case Study on CaGaSiN_3

摘要

The first gallium-containing nitridosilicate CaGa- SiN_3 was synthesized in newly developed high-pressure autoclaves using supercritical ammonia as solvent and nitriding agent. The reaction was conducted in an ammonobasic environment starting from intermetallic CaGaSi with NaN_3 as a mineralizer. At 770 K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070K (70-150 MPa). The impact of other mineralizers (e.g., LiN_3, KN_3, and CsN_3) on the product formation was investigated as well. The crystal structure of CaGaSiN_3 was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, ~(29)SiMAS-NMR, and first-principle DFT calculations. CaGaSiN_3 crystallizes in the orthorhombic space group Cmc2_1 (no. 36) with lattice parameters a=9.8855(11), b= 5.6595(1), c=5.0810(1) a, (Z=4, R_(wp)=0.0326), and is isostructural with CaAlSiN_3 (CASN). Eu~(2+) doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN_3:Eu~(2+) also represents an interesting candidate as a red-emitting material in phosphor- converted light-emitting diodes (pc-LEDs). In addition to the already known substitution of alkaline-earth metals in (Ca,Sr)AlSiN_3:Eu~(2+), inclusion of Ga is a further and promising perspective for luminescence tuning of widely used redemitting CASN type materials.