Neelam Malhan

Microwave gel combustion synthesis and sinterability of Nd:GGG nanopowders

Abstract Neodymium doped gadolinium gallium oxide (Nd:GGG) nanopowders synthesized by microwave gel combustion using alanine as a fuel was reported. Metal nitrates solution with alanine fuel was combusted in microwave to give precursor. The microwave precursor powder was calcined at different temperatures from 800 to 1100 °C. Phase pure Nd:GGG formation took place at 800 to 1100 °C as observed by X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) spectroscopy. However particle size increased with calcinations temperature from 25 nm at 800 °C to 200 nm at 1100 °C. Nd:GGG nanopowder obtained at different calcination temperatures were compacted and sintered at 1550 °C for 3 h in air. Most densified ceramic was obtained from Nd:GGG nanopowder calcined at 1100 °C. Microstructure as observed from scanning electron microscopy (SEM) showed that the most densified ceramic, obtained from nanopowder calcined at a higher calcination temperature, had a more uniform grain-size distribution, fewer pores and greater densification. XRD of sintered sample showed retention of phase purity.

Synthesis of Highly Sinterable Neodymium Ion doped Yttrium Oxide Nanopowders by Microwave Assisted Nitrate-Alanine Gel Combustion

Microwave assisted gel combustion synthesis of neodymium doped yttria (Nd:Y2O3) nanopowders using L-alanine complexing agent is being reported. Gelation of metal nitrates with L-alanine followed by combustion in microwave and subsequent calcinations at 1000°C for 3 h under oxygen supply gave phase pure nanopowders characterized by FTIR and XRD. Highly sinterable Nd:Y2O3 nanopowders with size range 20–80 nm, close to spherical and uniform morphology were obtained as observed by TEM compared to particles in size range 40–160 nm, with polyhedral morphology, obtained by sol-gel route. Compaction of calcined powders by cold isostatic press at 400 MPa followed by sintering at 1700°C for 7 h gave ceramic with 26% transmission which increased to 32% after 10 h without any sintering aid for microwave gel combustion compact, compared to 6.7% transmission for sol-gel route compacts. XRD of sintered samples showed retention of phase purity in all the cases. SEM of sintered samples showed good grain fusion for close to spherical particles of microwave assisted gel combustion route than polyhedral particles of sol-gel route. Since spherical particles undergo faster densification and sintering, microwave assisted route gave highly sinterable nanopowders compared to sol-gel route.

A novel comparative study of crystalline perfection and optical homogeneity in Nd:GGG crystals grown by the Czochralski technique with different crystal/melt interface shapes

Nd:GGG crystals (GGG is gadolinium gallium garnet) grown with different crystal/melt interface shapes (convex/flat/concave) by varying the seed rotation rate while using the Czochralski technique were studied for their optical homogeneity and crystalline perfection by optical polarization microscopy (OPM) and high-resolution X-ray diffractometry (HRXRD), respectively. It was found that there is a remarkable effect of seed rotation rate, which decides the shape of the crystal/melt interface, on the optical homogeneity and crystalline perfection. It was found experimentally that, as the rotation rate increases, the crystal/melt interface changes from convex to flat. If the rate further increases the interface becomes concave. With a steep convex interface (for low rotation rates), certain facets are concentrated in the small central portion of the crystal, and as the rate increases, these facets slowly move outward, leading to improved optical homogeneity and crystalline perfection as observed from the OPM and HRXRD results. The strain developed in the crystalline matrix as a result of segregation of oxygen in the crystals at low seed rotation rates as observed from HRXRD seems to be the reason for the observed optical inhomogeneity. The correlation between optical inhomogeneity and crystalline perfection for a variety of specimens with different shapes of the crystal/liquid interface obtained at different seed rotation rates is reported.

Single step low temperature synthesis of gadolinium gallium garnet nanopowders

Abstract Solution combustion synthesis of single-phase gadolinium gallium oxide (Gd 3 Ga 5 O 12 , GGG) nanopowders, by a fuel mixture approach using urea and glycine at a low temperature of 500 C, was being reported for the first time. Based on the fact that urea and glycine are good fuels for gallium oxide and gadolinium oxide synthesis, the fuel mixture composition was obtained, which could lead to direct phase pure cubic Gd 3 Ga 5 O 12 formation without any subsequent calcination step. Combustion was carried out in furnace pre-heated at 500 C. Thermogravimetric analysis (TGA) of combustion product showed negligible mass loss indicating direct formation of GGG powder. Fourier transform infrared (FTIR) spectrum of combusted product showed peak characteristic of GGG in case of mixed fuel. X-ray diffraction (XRD) confirmed formation of phase pure GGG at 500 C in preheated furnace. Very fine, well dispersed nanometric particles of size range of 50-100 nm were obtained, being uniform and close to spherical morphology as observed by transmission electron microscope (TEM).