Engineering topics

Katiyar, R. S.

Publications and source records attributed to Katiyar, R. S..

5 records

NASA NTRS2007

Temperature Dependent E2 Raman Modes in the ZnCoO Ternary Alloy

The anharmonic properties of low and high frequency E2 modes of ZnO and Co doped ZnO were investigated using Raman scattering spectroscopy. We have determined the behavior of frequency, linewidths, and lifetime of E2 modes in the temperature range from 80 to 800 K. In the case of E2(high) mode the frequency shift towards the lower energy side was analyzed in light of the theory of anharmonic phonon-phonon interaction and thermal expansion of the lattice, and the linewidth behavior was analyzed in terms of anharmonic effect of three-phonon decay mechanism. But in the case of E2(low), the linewidth and frequency behaved practically harmonic with respect to temperature and independent of Co substitutions. It is found that the E2(high) phonon anharmonicity is higher for ZnCoO alloys than in pure ZnO and it increases with the compositional disorder. The low temperature lifetime of E2 phonon in ZnO, 1 % and 3% Co doped ZnO were found to be 1.S2, 1.74, and 1.54 ps, respectively.

Samanta, K.↗

NASA NTRS2006

Raman Scattering Studies in Dilute Magnetic Semiconductor Zn(1-x)Co(x)O

Raman spectra of ZnO and Co substituted Zn1-xCoxO (ZCO) were carried out using the Raman microprobe system with an p.,+ ion laser source of 514.5 nm wavelength. The shift towards the lower frequency side of the nonpolar E210w mode and the broadening due to Co substitution in ZnO were analyzed using the phonon confinement model. The magnetic measurements showed ferromagnetic behavior with the maximum saturation magnetization (1.2micron Beta/ErCo) for 10% Co substitution, which decreased wi th at further increase in Co concentrations. The intensities of E1(LO) at 584 cm-1 and multiphonon modes at 540 cm-1 were increased with an increase in Co substitution. The additional Raman modes in ceramic targets of ZCO spectra for higher concentration of Co substitution (x=15%-20%) were identified to be due to the spinel ZnCo2O4 secondary phase.

Samanta, K.↗

NASA NTRS2002

Improved Dielectric Properties of Heterostructured Ba2.5Sr0.5TiO3 Thin Film Composites for Microwave Dielectric Devices

In the present work we have deposited MgO and Ba(sub 0.5)Sr(sub 0.5)TiO(sub 3)(BST50) thin layers in different sequences to make MgO:BST50 hetero-structured thin films. These films were characterized by X-ray diffraction and Rutherford backscattering technique and found to be highly (100) textured. The figure of merit {(C(sub0)-C(sub v)/(C(sub0-tandelta)} of the hetero-structured films was found to be higher as compared to pure BST50 films measured at 1 MHz frequency with electric field of 25.3 kV/cm. These films were used to make eight element coupled micro-strip phase shifter and characterized in a frequency range of 13-15 GHz. The high frequency figure of merit (kappa factor, defined as the ratio of degree of phase shift per dB loss) measured at around 14 GHz with electric field of 333 kV/cm has been markedly improved (around 64.28 deg/dB for hetero-structured film as compared to 24.65 deg /dB for pure film). Improvement in dielectric properties in a wide frequency range in the MgO:BST are believed to be due to the higher densification of the hetero-structured films.

Jain, M.↗

NASA NTRS1998

Raman and Photoluminescence Spectroscopy of Nano-crystalline PbTiO3 Sensor Materials with Different Doping Ions

Raman spectra & photoluminescence studies in PbTiO3, have been carried out, as a function of particle size, temperature, pressure and dopants. There appears respectively a distinct temperature-induced soft mode phase transition in each sample whose Curie temperature can be determined from the mean-field theory. The detailed Curie temperature shift in the modified PbTiO3 ceramics by Ba, Sr, La and Zr, has been investigated as a function of particle size. Pressure-induced phase transitions display an obvious diffuse behavior. Room temperature photoluminescence for nanocrystalline Ba(1-x)Pb(x)TiO3 have been observed. These studies favor preparations of high efficiency PbTiO3 sensors.

Katiyar, R. S.↗

NASA NTRS1997

A New Probe to Change Curie Temperature of PbTiO3 Sensors

High temperature Raman spectra of nanocrystalline Pb(0.8)Ba(0.2)TiO3, Pb(0.8)Sr(0.2) TiO3, Pb(0.8)La(0.2)TiO3 and Pb(0.8)Ba(0.2)TiO3, have been measured, as a function of particle size. There appears respectively a distinct temperature-induced soft mode phase transition in every sample whose Curie temperature can be determined from the mean-field theory. The detailed Curie temperature shift in modified PbTi03 ceramics by Ba, Sr, La, and Zr, has also been investigated as a function of particle size. This study will favor preparations of high efficiency PbTi03 sensors with an adjustable Curie temperature.

Katiyar, R. S.↗