Structural and luminescence studies of the new nitridomagnesoaluminate CaMg2AlN3

Abstract

CaMg₂AlN₃ was synthesized in a closed system by solid state reaction from binary nitrides. Structure refinements based on powder X-ray diffraction data suggested ambiguity about the occupancy of magnesium and aluminum tetrahedral sites. Solid-state ²⁷Al and ²⁵Mg NMR studies were used to adjudicate amongst possible space groups. With reference to projector augmented wave calculations of the quadrupolar coupling constants, the measured values of C_Q and the numbers of crystallographically inequivalent Al and Mg sites indicate that CaMg₂AlN₃ crystallizes in the space group P6₃/mmc with partial occupancy of the distorted tetrahedral Al site and possibly also mixing of Mg²⁺ and Al³⁺ ions on opposite sites. The compound obtained by synthesis with a flux shows orange defect-related luminescence at room temperature.