M.S. Multani

Synthesis of crystalline carbon nitride thin films by laser processing at a liquid–solid interface

Pulsed laser induced reactive quenching at a liquid–solid interface was used for the synthesis of tetrahedrally coordinated crystalline carbon nitride on a tungsten substrate. The crystalline phase was identified by transmission electron diffraction. X‐ray photoelectron spectroscopy indicated that the carbon atoms are coordinated only tetrahedrally with nitrogen—as expected for C3N4. The atomic percentage of N (considering only those atoms coordinated with C) is about 35%.

EFFECT OF PROCESS VARIABLES ON THE GRAIN GROWTH AND MICROSTRUCTURE OF ZNO-BI2O3 VARISTORS AND THEIR NANOSIZE ZNO PRECURSORS

The basic building block of the ZnO varistor is the ZnO grain formed as a result of sintering. Nanosized ZnO particles are prepared by carrying out the reaction in the controlled size nanoreactors—the droplets of microemulsions. Chemical doping of the ZnO nanoparticles provides ZnO-based ceramic varistors displaying superior varistor properties. These varistors show a higher value of the nonlinear coefficient, lower leakage current, and higher critical electric field value as compared to those for conventional samples in their log E versus log J curve. The present work has also been aimed at studying the effect of processing variables such as sintering temperature and duration on the microstructure and grain growth of ZnO nanoparticles and ZnO-Bi 2 O 3 ceramics. The activation energy calculated from this data is found to be 175 kJ/mol for pure ZnO. For Bi 2 O 3 -doped ZnO, the activation energy is found to decrease considerably (∼148 kJ/mol). All these advantages are due to greater structural homogeneity, smaller particle size, higher surface area, and higher density of the ZnO nanoparticles which are precursors for ZnO varistors, as compared to coarser particles for making varistors.

High-density PZT material

A simple sol-gel technique is shown to give >99% theoretical density Pb(ZrxTil−x)O3 ceramics with a breakdown voltage of more than 70 kV. cm−1 at 100°C. The piezoelectric tensor coefficient d33 is 293 × 10−12 coul. newton−1 for the x = 0.52 material. It is shown that processing parameters can be controlled easily.

Vibrational Spectroscopic Study of the Semiorganic Nonlinear Optical Crystal Bis(thiourea)cadmium Chloride

Polarized Raman and infrared spectra of bis(thiourea)cadmium chloride, a novel semiorganic nonlinear optical crystal, were recorded to determine the symmetries of molecular vibrations. The observed Raman and infrared bands are assigned to molecular vibrations of thiourea, cadmium–sulphur and cadmium–chloride bonds. The vibrational spectra are interpreted in the light of crystal structure data.

Dielectric properties of oriented thin films of PbZrO3 on Si produced by pulsed laser ablation

PbZrO3 is an antiferroelectric perovskite with TC≈230 °C. We have deposited single phase, perfectly c-axis oriented thin films of PbZrO3 on Si(100) substrates by pulsed laser ablation at 700 °C. The growth conditions (substrate temperature, ambient oxygen pressure, and laser energy density) have been optimized and the morphology of the films studied by scanning electron microscopy and atomic force microscopy. From a study of the dielectric hysteresis of the films and a measurement of the temperature dependence of their capacitance, we find that films thicker than ≈300 nm are antiferroelectric, while thinner films (<300 nm) appear to exhibit ferroelectric behavior.

c‐axis oriented ferroelectric thin films of PbTiO3 on Si by pulsed laser ablation

We have deposited single phase c‐axis oriented ferroelectric thin films of PbTiO3 on Si(100) by pulsed laser ablation technique in situ. It has been shown that the formation of a nonferroelectric, Pb2Ti2O6 pyrochlore phase at the interface could be avoided by raising the substrate temperature.

Secondary recrystallization during sintering of YBa2Cu3O7−gd derived from water-in-oil microemulsion

Abstract We report the occurrence of secondary recrystallization (exaggerated grain growth) during the sintering of YBa 2 Cu 3 O 7−δ synthesized from a water-in-oil microemulsion system. The microemulsion method leads to a microhomogeneous, uniform, finegrained precursor. Secondary recrystallization was not observed in the case of material synthesized from a conventional aqueous precipitation route but subsequently subjected to an identical thermal treatment. We compare the grain-growth kinetics in the samples produced from the microemulsion and the conventional aqueous precipitation routes. We point out some consequences of secondary recrystallization in the superconducting oxide.

Hot-sprayed yttrium iron garnet

Abstract Hot spraying (evaporative decomposition of solution) of sulfates of yttrium and iron at 1000°C and above produced powders which could be sintered to 99% X-ray density with homogeneous micro-structure and controlled grain size. The powder obtained from the hot-spray reactor was well gelated. However, no detectable YIG phase was obtained in the powder. The only constituents were YFeO 3 and Fe 2 O 3 . This is attributed to the fast nucleation of YFeO 3 phase in the reactor. The calcination studies of these powders showed that the conversion to YIG phase began above 900°C. The calcined powder with more than 90% conversion to YIG phase was still very fine and reactive. It could be sintered to high density product with average grain size ranging from 2 μ upwards.

Synthesis of polycrystalline YBa2Cu4O8 without the need of high oxygen pressure

Abstract Conventional methods of synthesis of the oxide ceramic superconductor YBa2Cu4O8 (1–2–4) require high oxygen pressure during synthesis and long heating schedules, making the process tedious and limited to a few groups. We report here the possibility of synthesis of 1–2–4 with a single firing in air. The technique involves formation, in solution, of a fine-particle-complex based precursor. The 1–2–4 phase then forms in air with a single firing of 30 minutes at 900°C and a Tc of 79.6K. The presence of 1–2–4 is confirmed by structural studies and then by thermogravimetric analysis.

Morphotropic phase boundary in the system Pb(ZrxTi1−x)O3

Abstract The room temperature phase boundary dividing the rhombohedral and tetragonal in the solid solution system lead zirconate titanate Pb(Zr x Ti 1−x )O 3 is examined carefully using an ultrahomogeneous synthesis technique. There is no evidence for a broad transition region of co-existing phases as understood earlier but a sharp boundary located at x = 0.510 ± 0.002.