Subir Roy

Dielectric properties of chemically synthesized PLZT and PZT: diffused phase transition and effect of lead non-stoichiometry

Dielectric and ferroelectric properties of chemically synthesized and sintered lead lanthanum zirconate titanate and lead zirconate titanate discs were studied. The as-burnt powders were directly sintered to 94% and 96% of the theoretical density at 1100 °C and 1200 °C, respectively for lead lanthanumm zirconate titanate (PLZT) and 96.7% at 1100 °C for lead zirconate titanate (PZT). The sintered PLZT samples showed improved dielectric properties whereas PZT showed improved ferroelectric properties compared with the data reported in the literature. Dielectric permittivity at room temperature of the 1100 °C sintered PLZT sample with grain sizes 0.4–1.2 µm was ~5000, at all measured frequencies. Evaporation of PbO from the sample generated micro inhomogeneity, which was detrimental for the dielectric property. A sintered PLZT sample underwent a completely diffused phase transition whereas a sintered PZT sample underwent a partially diffused phase transition. The measured values of remnant polarization of the 1100 °C sintered PZT and PLZT samples were 54.0 and 40.0 µC cm−2, respectively. The coercive fields observed for these samples were 13.3 and 7.7 kV cm−1, respectively.

Structural, ferroelectric and piezoelectric properties of chemically processed, low temperature sintered piezoelectric BZT–BCT ceramics

0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3TiO3) nanopowders were synthesized at very low temperature using a soft chemical approach. The synthesized powders and the consolidated disks were structurally characterized thoroughly by XRD, SEM, TEM and EPMA and also by ultraviolet and Raman spectroscopy. The 1350 °C sintered BZT–BCT disk displayed the highest density, underwent diffused phase transition centered at ~100 °C and showed the highest dielectric constant (8917) and lowest dielectric loss (0.015). The sintered BZT–BCT sample with the highest density showed a maximum polarization (P max) of 13 μC cm–2 and remnant polarization of 6 μC cm–2. The same sample exhibited very high electrostrain of ~0.12% under a relatively low electrical field of 3.5 kV mm−1.

Synthesis and study of magnetic properties of high temperature stable Ni nanoparticles in a nearly amorphous AlPO4 matrix in an oxidative atmosphere

Graphitized carbon coated Ni nanoparticles were synthesized in an AlPO4 matrix in situ in an oxidative atmosphere without using any foreign reducing agent. The Ni nanoparticles were evenly distributed in an inactive AlPO4 matrix and protected from the oxidation in air up to 900 °C. Carbon coating over the nanoparticles remained intact even when the samples were calcined at 900 °C in air. Magnetization of the Ni nanoparticles in the composite approached ∼89% of their bulk magnetization value when calcined at 900 °C in air. Magnetization increased with increasing the calcination temperature up to 900 °C.

Metastable face-centered cubic lead zirconate titanate (PZT) and lead lanthanum zirconate titanate (PLZT) nanocrystals synthesized by auto-ignition of metal-polymer gel

Nanocrystalline lead zirconate titanate (PZT) and lead lanthanum zirconate titanate (PLZT) have been synthesized in powder form by a single-step auto-ignition of metal–polymer gel precursor. The nanocrystalline powders were characterized using analytical transmission electron microscopy (TEM) equipped with an energy-dispersive x-ray spectrometer (EDXS) for composition analysis. For both PZT and PLZT, nanoparticles of sizes as low as 1–5 nm along with larger nanoparticles of sizes up to 30 nm are observed in the TEM. The selected-area diffraction (SAD) patterns from the nanoparticles revealed a face-centered cubic (fcc) crystal structure for both PZT and PLZT with a lattice parameter of ∼0.51 nm. The formation of PZT and PLZT nanoparticles of sizes below 5 nm with metastable fcc crystal structure has been observed for the first time. It is concluded that, as the crystal size decreases, the system assumes crystal structures of higher symmetry initially through small changes in lattice parameters and, in extreme cases, through chemical disorder for ultrafine nanoparticles.

Structural and Dielectric Properties of PMN-PT (65/35) Bulk Ceramics Synthesized by Metal-Polymer Gel Auto Ignition Route

Ultra-fine PMN-PT (65/35) powder was synthesized following a polymer precursor based chemical synthesis technique. The auto-ignited powder containing negligible amounts of carbonaceous residue (∼0.6 wt%) could be sintered directly without any further calcination. A mixture of perovskite and pyrochlore phase was detected in the auto-ignited powder by XRD analysis. The amount of pyrochlore phase decreased with increasing the annealing temperature and pure perovskite phase was obtained in the sample at 950°C. Scanning electron microscopy of the uniaxially pressed and sintered samples revealed the rectangular shaped grains. The dielectric properties of the sintered pellets were measured at room temperature.