K Sethupathi

Morphotropic phase boundary (MPB) Lead zirconate titanate [i.e Pb(Zr0.52Ti0.48)O3, PZT] is modified by incorporation of i) La in Pb-site, ii) simultaneously La in Pb-site and Nb in Zr/Ti site and iii) simultaneously La in Pb-site, Nb and Fe in Zr/Ti-site. Samples are prepared by alkoxide sol-gel synthesis. XRD study reveals peak shift towards lower 2á upon La addition but the shift is towards higher 2á for both La and Nb are incorporated. Addition of Fe makes peak shift towards higher angle but the amount of shift is very small with respect to that of La and Nb doping. The XRD data is further analyzed with the help of Rietveld refinement which reveals change in lattice parameters. It is observed that successive doping of La, La-Nb and La-Nb-Fe decrease both lattice parameters a and c.However, for the case of Nb and La co-doped PZT the value of c increases with respect to the c of only La doped PZT. The charge difference in Nb (5+) and Fe (3+) ions have compensating effect as they are doped in the same atomic site (i.e. B-site of the ABO3) which is having charge 4+. Raman spectroscopic study reveals more complex effect of successive multiple doping of La, Nb and Fe. Some of the observations in Raman spectroscopy are supportive to the observations made in XRD. Raman spectra are analyzed by cumulative fitting of de-convoluted peaks, which represent various individual vibrational modes: Reveal changes happening in the lattice due to the systematic successive doping of La, Nb and Fe.

Since the giant magnetocaloric effect is encountered in a ferromagnetic Gd5Si2Ge2 alloy near room temperature it is considered as a suitable material for magnetic refrigerator applications. Also a commensurate structural transition occurs at the magnetic transition temperature and there is a good correlation between the crystal structure and magnetic properties. Such observations have triggered numerous experimental studies on similar rare earth alloys and compounds. We have synthesized its Dy- analogue, namely, Dy5Si2Ge2 and have characterized it by means of room temperature X-ray diffraction, ac magnetic susceptibility (15 K-300 K), electrical resistivity (at zero field and at 6 T), thermoelectric power (15 K-300 K) and neutron diffraction (at 300 K and 9.2 K) experiments.

The electrical and magnetotransport properties of canted antiferromagnet Dy5Si2Ge2 are discussed. The DC electrical resistivity measurements confirm the magnetic crossover by a strong change of slope. The resistivity drops abruptly below TN as the spin disorder contribution vanishes. The application of magnetic field suppresses the TN by about 6 K thereby emphasizing the nature of the magnetic order to be antiferromagnetic.

Ce activated SrS has been prepared from SrSO 4:Ce(SO 4) 2.4H 2O by ecologically acceptable carbothermal reduction in the absence of inert gas and hazardous H 2S environment. The mixtures were fired at 900°C to find out the feasibility of the reduction reaction. In order to understand the compensator behavior we tried with sulfur and various fluxes viz., NH 4Cl, NaCl. The materials synthesized were characterized by XRD, photoluminescence emission (PL) and excitation spectroscopy (PLE) and SEM. The characterization results showed the formation of SrS at 900°C with an increase in luminescence intensity after the addition of sulfur as a co-activator. The bright blue-green emission observed at 480nm and 540nm corresponds to energy bands originating from 2T 2g (5d) to 2F 7/2, 2F 5/2(4f) of Ce 3+ transitions. The excitation spectrum shows a fundamental absorption of SrS host crystal lattice in the lower wavelength region at 283 nm and Ce at 430 nm. © 2005 Materials Research Society.

The paper presents the variation of structure and magnetism observed with the A-site composition of the double perovskite oxide Sr2-xPrxFeCoO6 (x = 0, 1, 2). The lattice symmetry was found to be lowered from tetragonal (x = 0) to orthorhombic (x = 2). With a ratio 1:1 of Sr and Pr, a highly asymmetric monoclinic structure is observed. The magnetic behavior of the middle member (x = 1) shows resemblance with that of Sr2FeCoO6, indicating the effect of Sr in the dilution of rare earth magnetism.

Graphite nanoplatelets (GNP) were prepared by thermal exfoliation of acid intercalated graphite and functionalized by acid treatment. The high pressure hydrogen adsorption-desorption measurements were carried out for f-GNP. The exfoliated f-GNP shows a hydrogen storage capacity of 0.5 wt % at 20 bar and 300 K. © 2011 American Institute of Physics.

In this paper, we show a simple circuit setup for experimentally plotting the v - i non-transversal pinched-hysteresis Lissajous fingerprint of a physical memristor - the common fluorescent gas discharge tube. The setup helped us investigate the effects of physical parasitics (inductors and capacitors) on the memristor v - i. © 2014 IEEE.

Hard magnetic ferrites or Hexa ferrites (AB12O19, A-Ba, Sr, Ca, Pb) are widely used as permanent magnets, in refrigerator seal gaskets, microphones, and speaker gaskets. They can also be used in small motors for cordless appliances and portable magnetic storage devices. In the present research, Al and Ce doped hexaferrites (AB12O19) were chosen and synthesized by combustion technique using the precursors (Sr(NO3)2, Ba(NO3)2, Ca(NO3)2, Fe(NO3)3, Al(NO3)3, Ce(NO3)3) and fuels (C6H8O7, C12H22O11). The prepared powder was calcined at different temperature (800 °C, 900 °C, 1100 °C) for 12 h. Phase identification was done by using X-Ray Diffraction (XRD) technique by which phases were confirmed and also the morphological behavior was studied by using Scanning Electron Microscopy (SEM). Elemental analysis was done by using Energy Dispersive Spectroscopy. The intrinsic magnetic properties were studied by using Vibrating Sample Magnetometer, and the hexaferrites are found to be affected by partial substitution of Sr and Fe sites by rare earth elements (RE3+) and non-magnetic trivalent Al3+ ions respectively, and it is same in case of BaFe12O19 and CaFe12O19. The insertion of Ce3+ and Al3+ into hexagonal lattice enhances the coercivity due to increase in magneto-crystalline anisotropy or grain refinement. Thus, the hexaferrites are doped by Ce and Al to achieve Sr0.9Ce0.1Fe10Al2O19, Ba0.9Ce0.1Fe10Al12O19, Ca0.9Ce0.1Fe10Al12O19.- 2019 Elsevier Ltd. All rights reserved.

Liquid Nitrogen (LN2) is used as an insulant as well as coolant in high temperature superconducting power equipments. Recently it is identified in HTSC transformers; the voltage distribution in the winding is oscillatory in nature. An attempt has been made to generate such unidirectional oscillatory impulse voltage (UOIV) of various frequencies to understand the breakdown characteristics of liquid nitrogen with non-uniform electric field configuration (Needle-Plane configuration). For the purpose of comparison breakdown characteristics under standard lightning impulse voltage were obtained. It is observed that the breakdown strength of UOIV and the lightning impulse voltage (LIV) are nearly same. The discharges initiated by UOIV in liquid nitrogen measured using Broadband sensor. It is observed that discharges occur at every peak of UOIV. It is high when the effective frequency of UOIV is high. It is also observed that number of discharges of various magnitudes occurs in the negative OIV. The magnitude of discharges is almost the same under positive polarity of UOIV. This high and low magnitude discharges can cause early failure of insulation. The signal measured using broadband sensor indicates that the signal lies in the UHF range. The result of the study indicates that PD occurs at the every peak of the applied OIV indicating severity of OIV. © 2013 IEEE.

The rare earth based transition metal perovskites are well known for their tunable physical properties. Here we present the dielectric response of the magnetic perovskite Eu2FeCoO6 from impedance spectroscopy measurements. The compound having a weak ferromagnetic ground state, is subjected to impedance spectroscopy measurements through the frequency range 100 Hz to 10 MHz for the temperature range 123 K-473 K. The dielectric permittivity shows huge values at high temperatures with low frequency. The two step relaxation process is inferred from Arrhenius fit.