Influence of calcination temperature on lattice parameters and particle size of R(2)CuO(4) compounds (R=Gd, Nd) prepared by a sol-gel

Cuprates R(2)CuO(4) (R = Gd, Nd) were prepared by a sol-gel method that allowed control of the mean particle size by calcining at different temperatures. The samples were characterized using X-ray diffractometry (XRD) and transmission electron microscopy. The results show that the structure of these cuprates is sensitive to the preparation method, particularly the calcination temperature, T-cal. The refined lattice parameters a and c, and unit-cell volume V, obtained from the XRD data by the Rietveld method, are found to decrease with increasing T-cal, while their mean particle size increased. Between 650 and 950 degrees C, the relative decreases in the lattice parameters were found to be larger for Gd2CuO4 than for Nd2CuO4 (e.g., 0.07 and 0.03%, respectively, for c). Furthermore, samples prepared by a standard solid state reaction had smaller lattice parameters than the samples prepared by the sol-gel method calcined at lower T-cal, while the values for the sol-gel samples calcined at higher T-cal approximate those for the solid state reaction samples. (C) 1996 Academic Press, Inc.