KNd(MoO₄)₂: A New Incommensurate Modulated Structure in the Scheelite Family

Potassium neodymium molybdenum oxide, KNd(MoO 4 ) 2, has been synthesized by the solid-state method. The structure and microstructure have been studied by X-ray powder diffraction and transmission electron microscopy (TEM). TEM revealed that the KNd(MoO 4 ) 2 structure is incommensurately modulated. The scheelite-like structure of KNd(MoO 4 ) 2 has been refined from X-ray powder diffraction intensities in the (3 + 1) D superspace group I 2/ b (αβ0)00 with a = 5.5202(2) Å, b = 5.33376(5) Å, c = 11.8977(3) Å, γ = 90.9591(7)°, and modulation vector q = 0.57789(4) a * − 0.14748(6) b * ( R P = 3.09%, R wP = 4.04%). The ordering of the K and Nd cations appears to be the primary parameter of the structure modulations. The compositional wave of the {KMoO 4 } and {NdMoO 4 } distribution is observed in the ab structure projection. The incommensurability of the compositional wave direction with respect to the a and b lattice constants is regarded as the origin of the incommensurate structure modulations.