Ammonothermal Synthesis of Novel Nitrides: Case Study on CaGaSiN3

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 microscopy, 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) AŠ, (Z=4, R_wp=0.0326), and is iso-structural 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 red-emitting CASN type materials.