Showing papers by "Harish Verma published in 2006"
TL;DR: In this article, it was shown that there are at least two characteristic particle size length scales for nanosize ZnFe2O4 particles prepared by the nitrate route, which are related to inversion of the cation distribution, agglomeration of particles and annihilation at the surface and in the interior.
Abstract: Nanosize zinc ferrite samples with an average particle size of 6–65 nm were prepared by a new chemical reaction involving nitrates of Zn and Fe and investigated for magnetic behaviour and defect structure. The sample with an average particle size of 6 nm has considerable inversion in cation distribution as shown by its hysteresis loop and increased magnetization. Mossbauer spectroscopy gives a single doublet for all the samples. Mossbauer parameters like quadrupole splitting and linewidth change sharply as the average particle size increases from 6 to 7 nm and then afterwards the changes are slow. The total Mossbauer absorption, on the average, increases with increase in particle size, the change from 6 to 65 nm being by a factor of 3. Positron parameters too change sharply as the particle size varies. The changes are related to inversion of the cation distribution, agglomeration of particles and annihilation at the surface and in the interior. The picture that emerges from the lifetime studies and supported by Mossbauer spectroscopy and magnetization studies suggests that there are at least two characteristic particle size length scales for nanosize ZnFe2O4 particles prepared by the nitrate route.
111 citations
TL;DR: The magnetization value for the smallest size ZnFe2O4 is much smaller than that for the other methods although it shows a nice hysteresis shape.
57 citations
TL;DR: In this paper, the authors used X-ray diffraction and optical spectroscopy to characterize Europium-doped Y 2 O 3 nanoparticles using an yttrium oxo-isopropoxide (Y 5 O(OPr i ) 13 ) as precursor.
25 citations
TL;DR: In this article, nano-sized barium titanate (BT) and Ce-doped BT samples were synthesized by simple hydrothermal technique at 150°C from Ba(OH) 2 ·8H 2 O, TiO 2 and Ce(NO 3 ) 3 ·6H2 O. The TEM micrographs confirmed the nano-size in similar range confirming the single crystallite nature of particles.
Abstract: Nano-sized barium titanate (BT) and Ce-doped barium titanate samples were synthesized by simple hydrothermal technique at 150 °C from Ba(OH) 2 ·8H 2 O, TiO 2 and Ce(NO 3 ) 3 ·6H 2 O. The mean crystallite diameters (MCD) along (1 0 1) plane obtained from XRD data were in the range of 24–28 nm for pure and Ce-doped samples. The TEM micrographs confirmed the nano-size in similar range confirming the single crystallite nature of particles. The room temperature emission spectra of Ce-doped and un-doped barium titanate were studied under ultraviolet irradiation. For pure BT the two peaks appeared at 396 and 521 nm, respectively. In case of Ce-doped BT two peaks centered around violet and green region were observed and the green luminescence was found to be sensitive to Ce concentration in the prepared samples.
12 citations
TL;DR: Mossbauer spectroscopic studies of two sedimentary layers from Petriccio section in Gubbio formation are presented in this paper, and it is found that these layers have almost the same iron phases nanophase hematite and phyllosilicate and with the same compositions as those in the Cretaceous-Tertiary Boundary (KTB) in PetricCio.
Abstract: Mossbauer spectroscopic studies of two sedimentary layers from Petriccio section in Gubbio formation are presented. It is found that these layers have almost the same iron phases nanophase hematite and phyllosilicate and with the same compositions as those in the Cretaceous-Tertiary Boundary (KTB) in Petriccio. The two layers also show enhancement in the siderophile elements such as Cr, Ni, Fe, Ca etc. to that found in the KTB layer. The two layers are well separated from the KTB layer, 128 and 149 cm below this layer, and show no enhancement of iridium. From the data it is suggested that the two layers also represent some kind of impact by extraterrestrial (ET) bolides.
1 citations