Illite crystallinity index from the Mesoproterozoic sedimentary cover of the Kaladgi basin, southwestern India: Implications on crustal depths of subsidence and deformation

The grade of metamorphism and thermal maturity of the Mesoproterozoic Bagalkot Group in the Kaladgi basin of southwestern India has been determined using the illite crystallinity (IC) index. IC index was determined from the argillite samples of four stratigraphic levels viz., Ramdurg Formation (basal unit), Yargatti Formation (intermediate lower unit), Yadahalli Formation (intermediate upper unit) and Hoskatti formation (upper unit). IC index (Kubler equivalent) values range between and (in a set of 37 samples) and indicate a deep diagenetic to high anchizone metamorphic grade within a temperature range of 180 to 300. The Mesoproterozoic sedimentary cover of the Kaladgi basin is deformed due to southerly directed gravity gliding of the cover over the basement. The general variation of the IC index along and across the basin as indicated by the distribution of IC index values and isocryst contour patterns is due to the combined effect of deformation and variable subsidence of the Mesoproterozoic cover of the basin. Considering an average Mesoproterozoic geothermal gradient of , the crustal depth of deformation and/or subsidence of the Mesoproterozoic cover up to the sample point is estimated to vary between 5.14 and 8.57 km

Room temperature multiferroicity in orthorhombic LuFeO3_3

From the measurement of dielectric, ferroelectric, and magnetic properties we observe simultaneous ferroelectric and magnetic transitions around $\sim$600 K in orthorhombic LuFeO$_3$. We also observe suppression of the remanent polarization by $\sim$95\% under a magnetic field of $\sim$15 kOe at room temperature. The extent of suppression of the polarization under magnetic field increases monotonically with the field. These results show that even the orthorhombic LuFeO$_3$ is a room temperature multiferroic of type-II variety exhibiting quite a strong coupling between magnetization and polarization.Comment: 5 pages with 5 figures; published in Appl. Phys. Let

Confinement creates a 9 GPa ambience: emergence of cristobalite phases in a silica film

We present here the results of the x-ray fluorescence (XRF), x-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Analysis of x-rays (EDAX), x-ray Reflectivity (XRR), Secondary Ion Mass spectroscopy (SIMS) and x-ray Diffraction (XRD) studies of silica films spin-coated from a Tetraethyl Orthosilicate (TEOS) precursor on native and hydrophilized Al substrates. It is observed that the substrates are mainly porous (porosity similar to 33%) AlO(OH), there is a diffuse interlayer of highly porous (porosity similar to 90%) AlO(OH), essentially a modification of the substrate, and a top layer of silica composed of nanocrystals with in-plane dimensions of 100-300 nm and thickness of 2.5 nm with a sharply defined silica-hydrated alumina interface. The silica nanocrystals were found in the metastable high pressure cristobalite phases with the tetragonal or alpha-phase co-existing in its low (0.77 GPa) and high (9 GPa) pressure structures. This indicates a high normal stress developed from the confinement and provides a basis for the quantitative assessment of the confinement force, which comes out to be higher in value than the van der Waals force but weaker than the Hydrogen bonding force

Enhanced Blue Emission from Transparent Oxyfluoride Glass Ceramics Containing Pr3+:BaF2 Nano-crystals

Transparent glass ceramics containing Pr3+:BaF2 nano-crystals in chemical composition of SiO2–BaF2–K2CO3–La2O3-Sb2O3 oxyfluoride glass systems have been prepared from melt quenching and with subsequent heat-treatment method. Luminescence and structural properties of these materials have been evaluated and the results are reported. Rietveld analysis of X-ray diffraction (XRD) patterns and investigation of transmission electron microscopy (TEM) confirmed the presence of BaF2 nano-crystals dispersed in the heat treated glass matrices. Measured UV-Vis-NIR absorption spectra have exhibited nine bands of the transitions 3H4 3P2, (1I6, 3P1), 3P0, 1D2, 1G4, 3F3,3F2, 3H6 and 3H5 from all the samples with non-degenerated 1I6 and 3P1 levels in the glass ceramics. The photoluminescence spectra show an enhancement in the intensities upon ceramization indicating the incorporation of Pr3+ ions in BaF2 nano-crystals which possess low phonon energy (346 cm-1). This has further been corroborated from the observation of a significant 3-fold increase in the relative intensity ratio of blue (3P0 3H4) to red (1D2 3H4, 3P0 3H6)emissions from glass-ceramics compared with the glass. It is due to a significant decrease of multiphonon non-radiative relaxation from 3P0 to 1D2 level of Pr3+ in glass ceramics. Time resolved spectra exhibit 3P0 level decays faster than 1D2 level

Ferromagnetism in transparent Mn(II)-doped indium tin oxide films prepared by sol-gel process

We observe remarkably strong room temperature ferromagnetism (~1.5 Bohr Magneton/Mn) in optically transparent Mn(II)-doped indium tin oxide (ITO) films. The nanocrystalline films with average grain size 10-22 nm and thickness 150-350 nm are prepared by sol-gel coating technique on sodalime silica glass substrate. The ferromagnetic property is, of course, weak for films deposited on pure silica glass substrate. The structural parameters of the films appear to be governing the magnetic property strongly which vary appreciably depending on the substrate. The observation of room temperature ferromagnetism in transparent conducting ITO films may find a plethora of applications in the area of magneto-optics.Comment: 17 pages including 3 figures; pdf onl

Phenomena and mechanism on phase transformation twinning in nanocrystalline BaTiO3

The detailed structure of nanocrystalline BaTiO 3 powder during ball milling has been studied using XRD & TEM. The study illustrates important advances in understanding atomic scale properties of this material. Ferroelectric BaTiO3 powder undergoes phase transformation along the sequence Cubic(Pm3m)-tetragonal(P4mm)-orthohombic (Amm2)-rhombohedral(R3m) structure when pressureless sintered samples are cooled from high temperature to low temperature. The high to low symmetry phases are not related to group subgroup symmetry as transformation is discontinuous and first order in nature and the twin relationship in me low symmetry is forbidden by Landau theory. In case of ball milled BaTiO 3 powder a continuous and diffusionless phase transition occur via second order to and from a metastable intermediate phase. In this pathway crystallites in the aggregation are twinned and the twin structure is related to crystal point group m3m which in the present case is illustrated as having 6mm symmetry formed under low driving force. The unit cell evolution due to phase transition and the crystallographic relationship are established.The phase transformation, coalescence and twin structure of thermally annealed BaTiO 3 nanocrystals under high vacuum has been investigated using in situ high temperature XRD. The structure analysis is performed with the use of the method of computer modelling of disorder structure and simulation of corresponding diffraction pattern. © 2010 Materials Research Society

Structural phase transitions during high-energy ball milling of BaTiO3

Microstructural characterization of ball milled perovskite BaTiO3 powders has been done by the modeling of X-ray diffraction profiles. The study reveals that on size reduction, BaTiO3 powders undergo a continuous, displacive, and diffusion-less dynamic phase transitions involving tetragonal (T), monoclinic (M), and orthorhombic (O) symmetry via the second-order type [T -> (T + M) -> (M + O) -> O] when stimulated by a high-power pulse of pressure in a planetary mill. The order parameter, a phenomenological quantity to describe the general behavior of a system going through phase transitions has been estimated using spontaneous strain calculated from lattice parameters or physical distortions derived from atomic coordinates or both. At room temperature, BaTiO3 nanoparticle achieved an orthorhombic phase when a critical size (= 70 h). Raman's study reveals similar structural phase transitions sequence on size reduction and TEM study reveals the corresponding particle diameter

Study of non-centrosymmetric to centrosymmetric structural transformation in Zr-doped Barium Titanate

Non-centrosymmetric to centrosymmetric structural transformation of BaZrxTi1-xO3 (x = 0, 0.05, 0.1, 0.3) as prepared by soilid state reaction was investigated from X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), pair distribution function (PDF) and Raman spectra. Tetragonal BaTiO3 transformed to orthorhombic phase for lower Zr concentration (x = 0.05) and changed to tetragonal to cubic with increasing Zr concentration at room temperature. Dielectric constant changed with the addition of Zr due to the change in local atomic arrangement and achieved highest value 1444 for mole fraction x = 0.1. Change occurred in the intensity for the first Ti-O pair in the PDF pattern due to the incorporation Zr in barium titanate lattice. An extra shoulder due to addition of Zr for the cubic phase of BZT has appeared at 5.64 angstrom in the PDF pattern. Structural and electrical properties of BZT were influenced by additions of Zr due to the change in local atomic arrangement