PREPARATION OF COPPER NIOBATES BY THERMAL-DECOMPOSITION OF FREEZE-DRIED COMPLEX OXALATE SOLUTIONS

Freeze-dried complex oxalates of copper and niobium are reactive precu rsors for ternary copper niobium oxides. The thermal decomposition of the amorphous precursors has been investigated by DTA, TG and mass spe ctroscopy. The gaseous decomposition products are assigned to steps in the TG graph. Above 500 degrees C, crystallization of complex oxides takes place. In the temperature range up to 900 degrees C, only the te rnary phases CuNb2O6 and Cu3Nb2O8 can be synthesized. The thermal deco mposition of the oxalate precursor is advantageous with regard to the preparation of pure monoclinic CuNb2O6. The transformation between mon oclinic and orthorhombic CuNb2O6 is reversible with a high activation energy of transformation.