High-pressure Raman investigation of high index facets bounded alpha-Fe2O3 pseudocubic crystals

[EN] High index facet bounded alpha-Fe2O3 pseudocubic crystals has gained the attention of the scientific community due to its promising electrochemical sensing response towards aqueous ammonia. The structural stability of alpha-Fe2O3 pseudocubic crystals is investigated through high-pressure Raman spectroscopy up to 22.2 GPa, and those results are compared with our ab initio theoretical calculations. The symmetry of the experimental Raman-active modes has been assigned by comparison with theoretical data. In addition to the Raman-active modes, two additional Raman features are also detected, whose intensity increases with compression. The origin of these two additional peaks addressed in this study, reveals a strong dependence on the geometry and the low dimensionality as the most plausible explanationNeravathu G Divya acknowledges DST FIST for FESEM analysis, Department of Physics, Cochin University of Science and Technology, Kerala, India. The author also acknowledges the Sophisticated Test and Instrumentation Centre (STIC), Kochi, India, for Rietveld Refinement measurements. This work is partly supported by Spanish MINECO under the projects MAT2016-75586-C4-2/3-P, FIS2017-83295-P, and MALTA Consolider Team project (RED2018-102612-T), and also by Generalitat Valenciana under project PROMETEO/2018/123-EFIMAT. JAS acknowledges the Ramon y Cajal program for funding supports through RYC-2015-17482 and VM to the Juan de la Cierva program through FJCI-2016-27921.Bushiri, MJ.; Gopi, DN.; Monteseguro, V.; Sans-Tresserras, JÁ. (2021). High-pressure Raman investigation of high index facets bounded alpha-Fe2O3 pseudocubic crystals. Journal of Physics Condensed Matter. 33(8):1-10. https://doi.org/10.1088/1361-648X/abcb11S11033

STRUCTURAL AND SURFACE MORPHOLOGICAL INVESTIGATION OF FORMATION STAGES OF HIGHLY (002) ORIENTED ZnO FILMS ON GLASS SUBSTRATES BY SPRAY PYROLYSIS METHOD

ZnO thin films were coated on amorphous glass substrate at various temperatures in the range 160-500 0 C by spray pyrolysis method. The as deposited films were characterised by using XRD and SEM. Wurtzite phase of ZnO was formed at a substrate temperature of 400 0 C, highly oriented (002) phase was developed with respect to increase of substrate temperature from 450 to 500 0 C. Morphological and growth mode of these films were analyzed with respect to structural orientation of films from wurtzite to highly (002) oriented phase. Present study reveals that substrate temperature was one of the important parameters which determine the crystalline quality, population of defects, grain size, orientation and morphology of the films

Photoluminescence Studies Of Microwave Assisted Synthesized Zno Micro Structures

ZnO micro particles in the range 0.4-0.6 μm were synthesized by microwave irradiation method. The XRD analysis reveals that the sample is in the wurtzite phase with orientation along the (101) plane. SAED pattern of the sample reveals the single crystalline nature of the micro grains. TEM images show the formation of cylindrical shaped ZnO micro structures with hexagonal faces. The optical phonon modes were slightly shifted in the Raman spectrum,attributed to the presence of various crystalline defects and laser induced local heating at the grain boundaries. A broad transmission profile was observed in the FTIR spectrum from 1550-3400 cm-1 which falls in the atmospheric transparency window region. PL spectrum centered at 500 nm with a broad band in the region 420-570 nm comprised of different emission peaks attributed to transition between defect levels. Various emission levels in the sample were expliained with a band diagramCochin University of Science and TechnologyJournal of Optoelectronics and Biomedical Materials Vol. 4, Issue 1, January-March 2012, p. 1 -

Raman and FTIR spectra of [Cu(H2O)6](BrO3)2 and [Al(H2O)6](BrO3)3 · 3H2O

Raman and FTIR spectra of [Cu(H2O)6](BrO3)2 and [Al(H2O)6](BrO3)3 · 3H2O are recorded and analyzed. The observed bands are assigned on the basis of BrO3 − and H2O vibrations. Additional bands obtained in the region of 3 and 1 modes in [Cu(H2O)6](BrO3)2 are due to the lifting of degeneracy of 3 modes, since the BrO3 − ion occupies a site of lower symmetry. The appearance 1 mode of BrO3 − anion at a lower wavenumber (771 cm−1) is attributed to the attachment of hydrogen to the BrO3 − anion. The presence of three inequivalent bromate groups in the [Al(H2O)6](BrO3)3 · 3H2O structure is confirmed. The lifting of degeneracy of 4 mode indicates that the symmetry of BrO3 − anion is lowered in the above crystal from C3v to C1. The appearance of additional bands in the stretching and bonding mode regions of water indicates the presence of hydrogen bonds of different strengths in both the crystals. Temperature dependent Raman spectra of single crystal [Cu(H2O)6](BrO3)2 are recorded in the range 77–523 K for various temperatures. A small structural rearrangement takes place in BrO3 − ion in the crystal at 391 K. Hydrogen bounds in the crystal are rearranging themselves leading to the loss of one water molecule at 485 K. This is preceded by the reorientation of BrO3 − ions causing a phase transition at 447 K. Changes in intensities and wavenumbers of the bands and the narrowing down of the bands at 77 K are attributed to the settling down of protons into ordered positions in the crystalSpectrochimica Acta Part A 58 (2002) 899–90

Solvo-hydrothermal growth and photoluminescence studies of micro and nano structured Zinc Sulfide for bio-imaging applications

The research on nanocrystalline materials have been of great interest for more than 20 years due to its fundamental properties as well as development of technology based on it. Non-toxic semiconducting nanocrystals are important materials with wide range of applications in the areas of biotechnology, medicine, bio-optics and for the fabrication light emitting and harvesting devices. Majority of the II-VI semiconductors possess wide band gap along with high iconicity and are important materials for optoelectronic devices operating under the UV excitation sources. Among the II-VI semiconductors, ZnS is a material with good optical transmission in the visible region with large exciton binding energy of about 40 meV. ZnS usually crystallizes in cubic form which is zinc blende or sphalerite and its hexagonal form is in wurtzite phase. The cubic sphalerite phase of ZnS has a band gap of 3.68 eV whereas the hexagonal (wurtzite) phase has a band gap of 3.77 eV. Moreover, ZnS is a good host lattice phosphor for photonic applications and electroluminescent devices because of its wide band gap. The present thesis deals with the synthesis and photoluminescence studies of micro and nanostructured ZnS by hydrothermal and solvo-hydrothermal method. Thesis is also focused on bioimaging application of these materials

Boosted UV emission at 349 nm from mesoporous ZnS

Relatively oxygen-free mesoporous cubic ZnS particles were synthesised via a facile solvo-hydrothermal route using a water–acetonitrile combination. Boosted UV emission at 349 nm is observed from the ZnS prepared by the solvo-hydrothermal route. The increased intensity of this UV emission is attributed to activation of whispering gallery modes of almost elliptical microstructures made of porous nanostructures.Cochin University of Science and TechnologyApplied Physics A (2013) 113:321–32

Vibrational spectroscopic studies of Guanidinium metal (MII) sulphate hexahydrates [MII = Co, Fe, Ni]

The Raman and FTIR spectra of [C(NH2)3]2M(SO4)2 ·6H2O (withM= Co, Fe, Ni) were recorded and analysed. The observed spectral bands are assigned in terms of vibrations of guanidinium ions, sulphate groups and water molecules. The analysis shows that the sulphate tetrahedra are distorted from their free state symmetry Td to C1. This is attributed to the presence of hydrogen bonds from water molecules. The order of distortion of the metal oxygen octahedra influenced the distortion of the sulphate tetrahedra. The appearance of 1– 3 modes of water molecules above 3300 cm−1 indicates the presence of weak hydrogen bondsCochin University of Science and TechnologySolid State Communications 143 (2007) 348–35

Structural And Surface Morphological Investigation Of Formation Stages Of Highly (002) Oriented Zno Films On Glass Substrates By Spray Pyrolysis Method

ZnO thin films were coated on amorphous glass substrate at various temperatures in the range 160-500 0C by spray pyrolysis method. The as deposited films were characterised by using XRD and SEM. Wurtzite phase of ZnO was formed at a substrate temperature of 400 0C, highly oriented (002) phase was developed with respect to increase of substrate temperature from 450 to 500 0C. Morphological and growth mode of these films were analyzed with respect to structural orientation of films from wurtzite to highly (002) oriented phase. Present study reveals that substrate temperature was one of the important parameters which determine the crystalline quality, population of defects, grain size, orientation and morphology of the filmsCochin University of Science and TechnologyJournal of Optoelectronics and Biomedical Materials Vol. 5 Issue 1, January - March 2013 p. 1 -