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Häusler, Jonas; Neudert, Lukas; Mallmann, Mathias; Niklaus, Robin; Kimmel, Anna-Carina L.; Alt, Nicolas S. A.; Schlücker, Eberhard; Oeckler, Oliver; Schnick, Wolfgang (2017): Ammonothermal Synthesis of Novel Nitrides: Case Study on CaGaSiN3. In: Chemistry-A European Journal, Vol. 23, Nr. 11: S. 2583-2590
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Abstract

The first gallium-containing nitridosilicate CaGa-SiN3 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 NaN3 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., LiN3, KN3, and CsN3) on the product formation was investigated as well. The crystal structure of CaGaSiN3 was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron mi-croscopy, 29SiMAS-NMR, and first-principle DFT calculations. CaGaSiN3 crystallizes in the orthorhombic space group Cmc21 (no. 36) with lattice parameters a= 9.8855(11), b= 5.6595(1), c= 5.0810(1) a, (Z= 4, Rwp= 0.0326), and is isostructural with CaAlSiN3 (CASN). Eu2+ doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN3: Eu2+ 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) AlSiN3: Eu2+, inclusion of Ga is a further and promising perspective for luminescence tuning of widely used redemitting CASN type materials.