Tapatee Kundu Roy

Observation of room temperature ferromagnetism in Mn–Fe doped ZnO

A room temperature ferromagnetic Fe doped ZnO bulk sample has been synthesized by co-doping 2 at% Mn with 2 at% Fe in ZnO. The final firing temperature for the preparation of the Zn0.96Mn0.02Fe0.02O sample is the same as the final firing temperature for the preparation of the Zn0.98Mn0.02O sample and in this case it is found to be 490 °C. It has been found that room temperature ferromagnetism in Zn0.96Mn0.02Fe0.02O is a factor of 1.6 times more than that observed in Zn0.98Mn0.02O samples. The size of the saturation magnetic field for the Zn0.96Mn0.02Fe0.02O sample is, however, only a factor of 7 times more than that observed for nanocrystalline undoped ZnO.

Defect studies in annealed ZnO by positron annihilation spectroscopy

Coincidence Doppler broadening of the positron annihilation technique has been employed to identify the defects in thermally annealed as-received ZnO and thermally annealed ball-milled nanocrystalline ZnO. Results indicate that a significant amount of oxygen vacancy has been created in ZnO due to annealing at about 500 °C and above. The results also indicate that the Zn vacancy created during the ball milling process can be easily removed by annealing the sample at about 500 °C and above. The defect characterization has also been correlated with the magnetic properties of ZnO.

33.7 MHz heavy-ion radio frequency quadrupole linac at VECC Kolkata

A 33.7 MHz heavy-ion radio frequency quadrupole (RFQ) linear accelerator has been designed, built, and tested. It is a four-rod-type RFQ designed for acceleration of 1.38 keVu, qA> or =116 ions to about 29 keVu. Transmission efficiencies of about 85% and 80% have been measured for the unanalyzed and analyzed beams, respectively, of oxygen ((16)O(2+), (16)O(3+), (16)O(4+)), nitrogen ((14)N(3+), (14)N(4+)), and argon ((40)Ar(4+)). The system design and measurements along with results of beam acceleration test will be presented.

Characteristics of Er2O3 Added ZnO-Based Varistor Ceramics

This study examines the effect of Er2O3 addition (0 to 2.0 mol.%) on microstructure and electrical characteristics of ZnO-based varistor ceramics prepared by high energy ball milling and sintering at 1200 °C for 1 h. With increasing Er2O3 content, the densification process diminishes marginally, but the grain size reduces dramatically due to the formation of Er-rich phases that inhibit grain coarsening specifically when the amount of Er2O3 addition is above 0.1 mol.%. The ZnO-based varistor modified with incorporation of 0.5 mol.% Er2O3 exhibits excellent varistor properties, since the breakdown field is increased from 1324 to 2320 V cm-1 and the nonlinear coefficient is enhanced from 23.1 to 27.4 when compared with the un-added ones.

Processing, characterization and properties of Er2O3 added ZnO based varistor ceramics

This article reports densification process, microstructural evolution and nonlinear electrical properties of Er2O3 (0–2.0xa0mol%) added ZnO–V2O5–MnO2–Nb2O5 varistor powder prepared by high energy ball milling followed by conventional (950–1350u2009°C, 1xa0h) sintering. Ball milled powder and sintered pellets have been characterized by density measurement, XRD analysis, TEM and SEM examinations coupled with EDS and image analyses for morphological modifications. Addition of Er2O3 is found to retard the ZnO grain growth significantly due to the formation of Er-rich spinel phases in the intergranular layer that reduces the grain boundary migration. Measurements of nonlinear electrical properties of sintered pellets reveal an enhancement in the breakdown field (E1mA) and corresponding nonlinear exponent (α) of Er added varistor samples. A typical varistor sample with 1xa0mol% Er2O3 sintered at 1200u2009°C exhibits ultrafine grain structure (grain size: 1.8xa0µm and sintered density: >96% theoretical density) with excellent nonlinear properties (E1mAu2009=u20096714xa0Vxa0cm−1 and αu2009=u200945).