Pika Jha

Synthesis, characterization and dielectric properties of nanometer-sized barium strontium titanates prepared by the polymeric citrate precursor method

Barium strontium titanate (BST) powders of the formula Ba1 − xSrxTiO3 (0 ≤ x ≤ 1) have been prepared for the first time by the polymeric precursor route using citric acid and ethylene glycol. Pure BSTs were obtained at 500 °C. These oxides were found to have the cubic structure, which is retained even after heating at 800 °C. Detailed X-ray studies on samples sintered at 1100 °C show weak tetragonal distortion for BaTiO3, while the other BSTs retain their cubic structure. The particle size of the sintered oxides increases from 55 nm for BaTiO3 to 88 nm for SrTiO3, from X-ray line-broadening studies. The nano-sized grains are reasonably stable to sintering (the particle size for BaTiO3 changes from 25 nm at 500 °C to 55 nm at 1100 °C). The dielectric constant of the sintered oxides decreases from 510 for BaTiO3 (x = 0) to 190 for SrTiO3 (x = 1) at 100 kHz. The dielectric loss decreases from 0.05 for BaTiO3 to 0.001 for SrTiO3 at 100 kHz. No ferroelectric transition was observed in either the dielectric studies or by differential scanning calorimetry.

Polymeric citrate precursor route to the synthesis of nano-sized barium lead titanates

Monophasic oxides of the formula, Ba1-xPbxTiO3 (0 less than or equal to X less than or equal to 1.0) were obtained at temperatures close to 500 degreesC from polymeric precursors formed using citric acid and ethylene glycol. These oxides were found to be tetragonal for all values of x, the distortion increasing with Pb content. Differential scanning calorimetry (DSC) shows that the decomposition of the precursor to the oxides varies with composition and the decomposition temperature is highest (530 degreesC) for the x = 0.5 composition. X-ray line broadening studies of 900 degreesC sintered samples show grain size of 50-54 nm in all compositions. TEM studies show agglomerated grains of the size, 40-60 nm. The dielectric constant (e) decreases with lead-doping having a value 70 for PbTiO3. The dielectric loss (D) for different compositions varied between 0.005 and 0.01 at 100 kHz. The dielectric constant and loss show excellent frequency stability.

Dielectric properties of lead zirconium titanates with nanometer size grains synthesized by the citrate precursor route

Monophasic oxides of the formula, PbZrxTii_xC>3 (0.0 < x < 0.75) were obtained at temperatures close to 500 °C from polymeric precursors formed using citric acid and ethylene glycol. The oxides were found to be tetragonal for lower values of x and rhombohedral for x = 0.75. X-ray line broadening studies along with transmission electron microscopy (TEM) show grain size in the range 50-60 nm for all the compositions. The dielectric constant of the above oxides increases with increase in Zr substitution and has a maximum value (e = 235) for PbZr0.75Ti0.25O3. The dielectric loss varies from 0.005 at 100 kHz and increases to 0.13 at 500 kHz.

New perovskite-related oxides having high dielectric constant: Ln2Ba2CaZn2Ti3O14 (Ln = La and Pr)

Two new oxides, La2Ba2CaZn2Ti3O14 and Pr2Ba2CaZn2Ti3O14, have been synthesized by the ceramic route at 1100°C. These oxides crystallize in the disordered cubic structure with an ‘a’ lattice parameter of 3.9728 (2) and 3.9448 (5) respectively. These oxides show high dielectric constant (70 and 57) and low loss (0.003 and 0.013 at 100 kHz) for La2Ba2CaZn2Ti3O14 and Pr2Ba2CaZn2Ti3O14 respectively. The dielectric constant is highly stable with frequency and temperature.

Nanoparticles of complex metal oxides synthesized using the reverse-micellar and polymeric precursor routes

Current interest in the properties of materials having grains in the nanometer regime has led to the investigation of the size-dependent properties of various dielectric and magnetic materials. We discuss two chemical methods, namely the reverse-micellar route and the polymeric citrate precursor route used to obtain homogeneous and monophasic nanoparticles of several dielectric oxides like BaTiO3, Ba2TiO4, SrTiO3, PbTiO3, PbZrO3 etc. In addition we also discuss the synthesis of some transition metal (Mn and Cu) oxalate nanorods using the reverse-micellar route. These nanorods on decomposition provide a facile route to the synthesis of transition metal oxide nanoparticles. We discuss the size dependence of the dielectric and magnetic properties in some of the above oxides

(La2/5Ba2/5Ca1/5)(Mn(2/5)-x Ni x Ti3/5)O3: Rietveld studies, dielectric and magnetic properties of new perovskite-related oxides

Oxides of the type (La2/5Ba2/5Ca1/5)(Mn(2/5)-xNixTi3/5)O3 (0 ≤ x ≤ 0.4) have been synthesized by the ceramic route. All the above oxides have been found to crystallize in the cubic perovskite structure. Rietveld refinement of the Ni-based oxide, (La2/5Ba2/5Ca1/5)(Ni2/5Ti3/5)O3 gave rise to a composition (La0.44Ba0.38Ca0.18) (Ni0.42Ti0.58)O2.85(6) and the refined lattice parameter obtained was 3.9411(2) Å (space group Pm3m;R(F2) = 0.026,Rp = 0.074,wRp = 0.087). A shift from antiferromagnetic to paramagnetic behaviour is observed with increase in nickel concentration, the Mn-rich phases showing antiferromagnetism around 5 K. There is a systematic decrease in the dielectric constant, ε and loss tangent with increase in Ni concentration (from ε = 592 forx = 0 to ε = 78 forx = 0.4).