Synthesis and structural characterization of K 0.33Gd 0.67F 2.33 (KGd 2F 7) and K 0.31Gd 0.69F 1.84O 0.27

Abstract

K 0.33Gd 0.67F 2.33(KGd 2F 7) is synthesized by solid state reaction between KF and GdF 3 at different temperatures (600, 700, 800 and 900 °C). For all temperatures, the crystal structure of K 0.33Gd 0.67F 2.33 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 °C is determined by the Rietveld method. The oxyfluoride K 0.31Gd 0.69F 1.83O 0.27 is synthesized using a sol–gel route. Its crystal structure is close to that of K 0.33Gd 0.67F 2.33 and differs only by a new anionic and cationic ordering. K 0.33Gd 0.67F 2.33 and K 0.31Gd 0.69F 1.83O 0.27 are then just particular compositions of the solid solution formulated K 1 − x Gd x F 1 + 2 x − 2 y O y .