Chemical synthesis and characterization of nano-sized rare-earth ruthenium pyrochlore compounds ${\text{Ln}}_2{\text{Ru}}_2{\text{O}}_7$ (Ln = rare earth)

The rare-earth ruthenium pyrochlores ${\text{Ln}}_2{\text{Ru}}_2{\text{O}}_7$ ($\text{Ln}={\text{La}}^{3+}$, ${\text{Pr}}^{3+}$, ${\text{Nd}}^{3+}$, ${\text{Sm}}^{3+}$ and ${\text{Gd}}^{3+}$) have been synthesized by the tartrate co-precipitation method, which allowed control of their composition and morphology. The preparation processes were monitored by thermal studies (TG-DTA). The obtained ruthenates were characterized by X-ray diffraction (XRD), TEM, d.c. electrical conductivity, thermoelectric power and dielectric constant measurements. X-ray diffraction patterns for all pyrochlore samples indicate a single-phase crystalline material with a cubic structure except for ${\text{LaRuO}}_3$, which shows perovskite orthorhombic structure. The structural parameter for the solid obtained was successfully determined by Rietveld refinement based on the analysis of powder XRD pattern. The TEM photographs of these compounds exhibited the average particle size in the range of 36.4–73.8 nm. The data on the temperature variation of d.c. electrical conductivity showed that all rare-earth ruthanates are semiconductors and major carriers are electrons. The conduction mechanism of these compounds seems to be oxygen non-stoichiometry. The variation of dielectric constant at various frequencies showed initially interfacial polarization up to 275 kHz and beyond, which shows domain wall motion.