Synthesis and structural characterization of K0.33Gd0.67F2.33 (KGd2F7) and K0.31Gd0.69F1.84O0.27

K0.33Gd0.67F2.33(KGd2F7) is synthesized by solid state reaction between KF and GdF3 at different temperatures (600, 700, 800 and 900 deg C). For all temperatures, the crystal structure of K0.33Gd0.67F2.33 derives from that of the fluorite type. Nevertheless when the synthesis temperature increases, the X-ray powder pattern exhibits new superstructure diffraction lines. This feature is attributed to an anionic and cationic ordering. A structural model is elaborated and the crystal structure at 700 deg C is determined by the Rietveld method. The oxyfluoride K0.31Gd0.69F1.83O0.27 is synthesized using a sol-gel route. Its crystal structure is close to that of K0.33Gd0.67F2.33 and differs only by a new anionic and cationic ordering. K0.33Gd0.67F2.33 and K0.31Gd0.69F1.83O0.27 are then just particular compositions of the solid solution formulated K1-xGdxF1+2x-2yOy.