The title compound, potassium niobium aluminium arsenate (KNAA), is isostru
ctural with KTiOPO4 (KTP). In KNAA, the site corresponding to the Ti1 sites
of KTP is occupied mostly by Nb atoms, the Ti2 site is occupied predominan
tly by A1 atoms, and the As1 and As2 tetrahedral sites are occupied mostly
by As atoms. The M1O(6) octahedron is more distorted and the M2O(6) octahed
ron is less distorted than that of KTP.