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 tha t allowed control of the mean particle size by calcining at different temperatures. The samples were characterized using X-ray diffractometr y (XRD) and transmission electron microscopy. The results show that th e structure of these cuprates is sensitive to the preparation method, particularly the calcination temperature, T-cal. The refined lattice p arameters 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, w hile their mean particle size increased. Between 650 and 950 degrees C , the relative decreases in the lattice parameters were found to be la rger for Gd2CuO4 than for Nd2CuO4 (e.g., 0.07 and 0.03%, respectively, for c). Furthermore, samples prepared by a standard solid state react ion had smaller lattice parameters than the samples prepared by the so l-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 stat e reaction samples. (C) 1996 Academic Press, Inc.