The rare-earth ruthenium pyrochlores Ln$_2$Ru$_2$O$_7$ (Ln $=$ La$^{3+}$, Pr$^{3+}$, Nd$^{3+}$, Sm$^{3+}$ and 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 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.

Cerium vanadate (CeVO$_4$) and zirconium titanate (ZrTiO$_4$) powders have been synthesized by the dicarboxylate coprecipitation method. The formation of precursors and mixed oxides was confirmed by their elementaland thermal analysis (thermogravimetric analysis–differential thermal analysis), infrared spectroscopy (Fourier transform infrared), X-ray fluorescence spectroscopy, energy-dispersive X-ray analysis and powder X-ray diffraction. X-ray analysis reveals the formation of a single-phasic CeVO$_4$ with tetragonal structure and ZrTiO$_4$ with orthorhombic structure. The morphological characteristics of these oxides were studied by field-emission scanning electron microscopy and a laserbased particle size analyzer. Different solid content and dispersants have been used to prepare various suspensions of these oxides in distilled water and ethanol. The rheological flow behaviour of the suspensions has been studied by measuring their viscosity against the increasing shear rate. The power-law model is applied to calculate consistency coefficient (k) and flow behaviour index (n). Minimum viscosities have been observed at pH = 10.6 for CeVO$_4$–water–Darvan system and at pH = 10.5 for ZrTiO4–water–polyethylene imine system.