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Effect of Fe³⁺ substitution on structural and macro-magnetic properties of yttrium iron garnet

Mon, 01 Dec 2003 00:00:00 GMT

Title: Effect of Fe³⁺ substitution on structural and macro-magnetic properties of yttrium iron garnet Authors: Modi, Kunal B; Shah, H J; Trivedi, U N; Vara, R P; Chhantbar, M C; Joshi, H H Abstract: The structural and bulk magnetic properties of Fe³⁺ substituted yttrium iron garnet with general formulaY_3-xFe_5+xO₁₂ (x = 0.0, 0.05, 0.15,0.30 and 0.50) have been investigated by means of X-ray diffraction, EDAX, high field magnetization and low field a.c. susceptibility measurements. It is found that substituted Fe³⁺ ions occupy c-sites and increase in lattice constant for x> 0.30 is due to presence of Fe²⁺ ions, determined through EDAX, on a-sites. Variation of magneton number with x can be explained satisfactorily assuming the collinear spin ordering model and Neel temperature values deduced experimentally from a.c. suscepti bility measurements are in good agreement to those calculated theoretically. Page(s): 502-506

Glass forming ability of Te-Bi-Se based alloys

Mon, 01 Dec 2003 00:00:00 GMT

Title: Glass forming ability of Te-Bi-Se based alloys Authors: Saxena, Manish; Agarwal, Animesh; Bhatnagar, P K Abstract: In the present work, the relationships for the glass transition temperature T_g, the peak temperature T_p, and the difference of crystallization temperature and glass transition temperature, (T_c - T_g), for different heating rates have been studied with the increase in Bi content. With the increase in heating rates T_g, T_c and T_p are found to increase. The glass transition temperature represents the strength or rigidity of the glass structure. This analysis helps in finding the suitability of an alloy to be used in phase transition optical memories/ switches. Page(s): 498-501

Dielectric properties and a.c. electrical conductivity of aqueous solution grown pure and iodine doped poly (vinyl alcohol) films

Mon, 01 Dec 2003 00:00:00 GMT

Title: Dielectric properties and a.c. electrical conductivity of aqueous solution grown pure and iodine doped poly (vinyl alcohol) films Authors: Sengwa, R J; Kaur, Kulvinder Abstract: Poly vinyl alcohol (PVA) films of uniform thicknesses 280, 120, 80, 50 and 25 microns, and also 50 micron PVA films doped with 4, 3, 2 and 1 wt% iodine of PVA weight in aqueous solution have been prepared by solution grown technique. Ag-PVA-Ag sandwich structures of film capacitors have been fabricated for their dielectric characterization. The capacitance and dissipation factor of these capacitors are measured in the frequency range 100Hz-100 kHz at 25°C. The dielectric permittivity ɛ', loss ɛ", and a.c. conductivity σ, have been determined using the measured values of capacitance and dissipation factor. It is found that the value of ɛ' decreases with increase in frequency and increases with the film thickness while dielectric loss ɛ" shows marked variation with frequency. For iodine doped films, values of ɛ' and ɛ" vary anomalously with the increase in concentration of iodine. From the a.c. conduction studies, it is observed that the a.c. conductivity of pure PVA films increases with the film thickness and vary almost linearly with frequency in the range of 10-¹¹ -10^-8 S cm^-1. Further it is found that there is anomalous variation in conductivity of iodine doped PVA film with increase in iodine concentration. From these dielectric studies, it seems that an increase in ɛ' and ɛ" with the increase in PVA film thickness is due to the residual water or variation in degree of syndiotacticity of PVA chain. In case of iodine doped PVA films, the variations in crystalline and complex formation of PVA molecules with iodine are responsible to change the dielectric parameters. Page(s): 492-497

Biofilm formation on structural materials in deep sea environments

Mon, 01 Dec 2003 00:00:00 GMT

Title: Biofilm formation on structural materials in deep sea environments Authors: Venkatesan, R; Dwarakadasa, E S; Ravindran, M Abstract: Biofilm formation on structural materials in deep-sea environment after long duration of exposure is reported here for the first time. Some structural material specimens such as steel, steel with zinc and aluminum anodes and carbon fibre-reinforced composite were exposed at depths of 500, 1200, 3500 and 5100 m for 174 days. The bacterial colony formation on these specimens was studied after their retrieval from the ocean. Macrofouling was not found in any of these materials. Carbon fibre-reinforced composite did not support bacterial colony formation at all the tested depths. Steel supported bacterial colonies at all depths. Aluminium and zinc anodes did not support bacterial colonies at 3500 and 5100 m depths. This could be related to lower temperatures prevailing at these depths. Also, all the identified bacterial colonies were aerobic as dissolved oxygen was present even at 5100 m depth. Hence, anaerobic conditions did not exist during exposure under these structural conditions. Dissolved oxygen data at the experimental site is also presented and discussed. Page(s): 486-491

NOPR Community:

Effect of Fe3+ substitution on structural and macro-magnetic properties of yttrium iron garnet

Glass forming ability of Te-Bi-Se based alloys

Dielectric properties and a.c. electrical conductivity of aqueous solution grown pure and iodine doped poly (vinyl alcohol) films

Biofilm formation on structural materials in deep sea environments

Effect of Fe³⁺ substitution on structural and macro-magnetic properties of yttrium iron garnet