Monophasic Sn1−xCoxO2 (x = 0.05, 0.10, and 0.15) nanoparticles with tetragonal structure have been successfully synthesized by solvothermal method using oxalate precursor route. Powder x-ray diffraction and selected area electron diffraction studies confirmed highly crystalline cassiterite SnO2 structure. The contraction of lattice constants confirmed the incorporation of Co2+ in SnO2 host lattice. Hexagonal nanoparticles with average grain size of 8–13 nm have been formed. With the increasing Co content, the decreasing crystallite size of SnO2 with increasing surface areas from 194 to 219 m2/g was found. The percentage reflectance increases on increasing the cobalt concentration, and a noticeable blue shift appeared. The band gap was found to be 3.85, 3.91, and 4.09 eV, respectively. Co-doped SnO2 showed distinct magnetic behavior with different Co2+ concentration. For x = 0.05 and 0.10, nanoparticles showed paramagnetism with antiferromagnetic interaction, however, on further increasing x = 0.15, the nanoparticles showed canted antiferromagnetic coupling.

A simple and modified solvothermal method using oxalate precursor, used to synthesize Cd1−xNixO (x = 0.047, 0.102, and 0.163) nanoparticles and their phase structure, morphology, optical and magnetic properties, have been investigated. X-ray diffraction studies revealed that as-prepared Ni-doped CdO solid solutions are highly crystalline and stabilized in a monophasic cubic CdO structure. X-ray diffraction and ICP-MS studies confirmed the incorporation of Ni2+ in a CdO matrix. The average grain size was found to be 30, 15, and 11 nm, respectively, using transmission electron microscopic studies. High surface area in the range of 118–143 m2/g has been achieved for these solid solutions using the multipoint BET method, which increases on increasing Ni concentration in Cd lattice site. The optical band gap of these solid solutions shows red shift to the undoped CdO. Ni-doped CdO nanoparticles exhibit co-existence of paramagnetism and ferromagnetism.

Nanosized oxides of barium strontium zirconate of general formula Ba1-xSrxZrO3 (0 ≤ x ≤ 1) have been prepared over the entire range of x for the first time by polymeric precursor route using citric acid and ethylene glycol. These solid solutions were investigated by means of powder x-ray diffraction, transmission electron microscopy, scanning electron microscope and Brunauer, Emmett and Teller surface area studies. X-ray diffraction studies reveal the monophasic nature of the powders at 1000 °C. The grain size was found to be in the range of 17–52 nm for all the oxides at 1000 °C. Specific surface area of these solid solutions comes out to be in the range of 49.1–94.4 m2/g. Smallest particle size with highest surface area has been achieved for x = 0.25 and comes out to be 17 nm and 94.4 m2/g respectively. Dielectric constant (ε) and dissipation factor (D) were investigated as a function of frequency and temperature. The room temperature dielectric constant of Ba1-xSrxZrO3 was found to be maximum 105 for x = 0.20 at 1 MHz.

Solid solutions of Ba1−xPbxZrO3 (0 ≤ x ≤ 0.75) have been synthesized successfully by polymeric citrate precursor method for the first time. The solid solutions were characterized by powder x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and surface area studies. XRD studies reveal the monophasic nature of these highly crystalline nanoparticles (except few impurity of ZrO2 in PbZrO3). Lattice parameter of Ba1−xPbxZrO3 (0.20 ≤ x ≤ 0.75) decreases with increasing the Pb content. Dielectric properties of these nanoparticles were investigated as a function of frequency and temperature. The dielectric constant for x = 0.15 showed a maximum value of 75.5.

Sintered compacts of nano-sized and micron-sized BaTiO3 show sharp ferroelectric transition and high dielectric constant at specific compositions. The sintered compacts with 1 wt% nano-BaTiO3 show a maximum dielectric constant of 1680. At the transition temperature (Tc) there are two maxima at 0.5 and 2 wt%. The variation in the dielectric constant at Tc is also reflected in the behavior of the ferroelectric transition as studied by differential scanning calorimetry. This interesting oscillatory variation of the dielectric constant and dielectric loss with increase in the amount of nanoparticles in the sintered compacts is observed for the first time. The variation of the dielectric properties and the ferroelectric transition of the sintered compacts could be related to subtle changes in the microstructure.

A modified and convenient route using microemulsions (avoiding Ba-alkoxide) was evolved for the synthesis of uniform and monodisperse nanoparticles of BaTiO3 at low temperature (800 °C). X-ray line broadening and transmission electron microscopy studies show that the particle size varies in the range of 20–25 nm. Evidence for tetragonal distortion was found in these nano-sized (20–25 nm) particles of barium titanate from careful x-ray diffraction studies as well as from Raman spectroscopy. Our study showed that the critical size of the cubic to tetragonal transition in barium titanate may be much lower than suggested theoretically. The grain size showed an increase on sintering of 35 nm at 900 °C to 120 nm at 1100 °C, which was much lower than the grain size obtained at this temperature by the normal solid state route. The dielectric constant depends on sintering temperature and was found to increase from 210 (900 °C sintering) to 520 (1100 °C sintering) at 100 kHz. The dielectric constant was highly stable with temperature as well as frequency.

Nanoparticles of barium orthotitanate (Ba2TiO4) was obtained using microemulsions (avoiding Ba-alkoxide). Powder x-ray diffraction studies of the powder after calcining at 800 °C resulted in a mixture of orthorhombic (70%) and monoclinic (30%) phases. The high-temperature orthorhombic form present at 800 °C was due to the small size of particles obtained by the reverse micellar route. Pure orthorhombic Ba2TiO4 was obtained on further sintering at 1000 °C with lattice parameters a = 6.101(2) Å, b =22.94(1) Å, c = 10.533(2) Å (space group, P21nb). The particle size obtained from x-ray line broadening studies and transmission electron microscopic studies was found to be 40–50 nm for the powder obtained after heating at 800 °C. Sintering at 1000 °C showed increase in grain size up to 150 nm. Our studies corroborate well with the presence of a martensitic transition in Ba2TiO4. The dielectric constant was found to be 40 for Ba2TiO4 (at 100 kHz) for samples sintered at 1000 °C. The dielectric loss obtained was low (0.06) at 100 kHz.