New pyrochlore-type oxides in Ca-R-Ti-Nb-O system (R=Y, Sm or Gd)--structure, FT-IR spectra and dielectric properties

摘要

New pyrochlore-type oxides in the Ca-R-Ti-Nb-O system, Ca_3R_3Ti_7Nb_2O_(26.5) (RY, Gd or Sm), have been prepared for the first time. Powder X-ray diffraction (XRD) was used for the phase identification, and it was found that pure pyrochlore-type phase is formed. FT-IR spectra of the compounds also show the absorption bands corresponding to the pyrochlore structure including two absorption bands at about 660-680 cm~(-1) followed by a broad weak absorption at 870-900 cm~(-1) for all corresponding to B-O stretching vibration. Microstructure studies reveal that the compounds are densified at 1350 deg C and the grains are in the size range 1-6 (mu)m. Dielectric measurements show that dielectric constant of all the compounds are in the 53-70 range and loss factor ranges from 0.0082 to 0.0096 at 1 MHz. Resistivity of all the compounds are greater than 10~8 OMEGA cm at room temperature.