Signatures of electron-boson coupling in half-metallic ferromagnet Mn5_5Ge3_3: study of electron self-energy Σ(ω)\Sigma(\omega) obtained from infrared spectroscopy

We report results of our infrared and optical spectroscopy study of a half-metallic ferromagnet Mn$_5$Ge$_3$. This compound is currently being investigated as a potential injector of spin polarized currents into germanium. Infrared measurements have been performed over a broad frequency (50 - 50000 cm$^{-1}$) and temperature (10 - 300 K) range. From the complex optical conductivity $\sigma(\omega)$ we extract the electron self-energy $\Sigma(\omega)$. The calculation of $\Sigma(\omega)$ is based on novel numerical algorithms for solution of systems of non-linear equations. The obtained self-energy provides a new insight into electron correlations in Mn$_5$Ge$_3$. In particular, it reveals that charge carriers may be coupled to bosonic modes, possibly of magnetic origin

Behavior and Impact of Zirconium in the Soil–Plant System: Plant Uptake and Phytotoxicity

Because of the large number of sites they pollute, toxic metals that contaminate terrestrial ecosystems are increasingly of environmental and sanitary concern (Uzu et al. 2010, 2011; Shahid et al. 2011a, b, 2012a). Among such metals is zirconium (Zr), which has the atomic number 40 and is a transition metal that resembles titanium in physical and chemical properties (Zaccone et al. 2008). Zr is widely used in many chemical industry processes and in nuclear reactors (Sandoval et al. 2011; Kamal et al. 2011), owing to its useful properties like hardness, corrosion-resistance and permeable to neutrons (Mushtaq 2012). Hence, the recent increased use of Zr by industry, and the occurrence of the Chernobyl and Fukashima catastrophe have enhanced environmental levels in soil and waters (Yirchenko and Agapkina 1993; Mosulishvili et al. 1994 ; Kruglov et al. 1996)

Temperature Induced Changes in Morphology and Structure of Tio2-al2o3 Fibers

Electrospinning of a sol-gel and polymer mixture is used to produce titania-alumina (TiO2–Al2O3) fibers with diameters ranging from 200 to 800 nm. These composite metal-oxide fibers were calcined at various temperatures and their morphology is studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The decrease in the average diameter of the fibers with increasing temperature is observed. Powder X-ray diffraction (XRD) reveals that up to 800 °C the composite fibers have anatase titania structure whereas at 900 °C the fibers exhibit mixture of anatase and rutile phases. It is found that specific surface area decreases as a function of temperature in the 700–900 °C range. The change in phase (anatase-to-rutile) and the increase in crystallite size occur simultaneously. The presence of smaller amount of amorphous alumina in the primarily titania-based structure seems to play the role in stabilizing the anatase phase

Fabrication and Characterization of Tio2--zno Composite Nanofibers

Tetraisopropyl titanate, zinc acetate dihydrate, and polyvinylpyrrolidone (PVP) were mixed to obtain a composite solution for producing TiO2–ZnO nanofibers. Electrospinning and subsequent calcination at 973 K were employed to produce composite metal-oxide nanofibers with diameters ranging from 50 to 150 nm. Characterization of the TiO2–ZnO composite nanofibers was carried out by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (XEDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible (UV–vis) spectrophotometry. TGA reveals a total weight loss of 49% and no change in mass above 873 K. The nanofibers are predominantly made of titania and exhibit two different energy band gap values of 3.0 and 3.5 eV. Our findings indicate that in the composite TiO2–ZnO nanofibers three different phases (anatase and rutile TiO2 and wurtzite ZnO) can co-exist and retain their individual characteristic properties

Characterization of Tio 2--al 2 O 3 Composite Fibers Formed by Electrospinning a Sol--gel and Polymer Mixture

Composite fibers of TiO2–Al2O3 were prepared by electrospinning a sol–gel and polymer mixture to form template polymeric fibers followed by calcination. The resulting fibers were characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), diffuse reflectance ultraviolet–visible (UV–vis) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (XEDS), and X-ray photoelectron spectroscopy (XPS). Calcination at 973 K resulted in mixture of anatase (A) titania and gamma (γ) alumina phases. We calculated a band gap energy of 3.3 eV and found the average diameter of the resulting fibers in the 150–400 nm range. Both XEDS and XPS reveal that fibers are predominantly made of titania

Selective emitters for thermophotovoltaics: erbia-modified electrospun titania nanofibers

Titania nanofibers were synthesized by electrospinning and characterized with scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The nanofibers were annealed to 773 K to achieve the anatase titania crystal structure, and to 1173 K to obtain the rutile phase. In order to create erbia-containing titania nanofibers, erbium (III) oxide particles were added to the pre-cursor solution before electrospinning. After pyrolysis the titania nanofibers supported and encapsulated the erbia particles. Temperature-dependent near-infrared emission spectra demonstrate that the erbia-containing nanofibers emit selectively in the range 6000–7000 cm−1. Because of their large surface to volume ratios and narrow-band optical emission, these nanofibers can be used as selective emitters for thermophotovoltaic applications

Selective Emitters for Thermophotovoltaics: Erbia-modified Electrospun Titania Nanofibers

Titania nanofibers were synthesized by electrospinning and characterized with scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The nanofibers were annealed to 773 K to achieve the anatase titania crystal structure, and to 1173 K to obtain the rutile phase. In order to create erbia-containing titania nanofibers, erbium (III) oxide particles were added to the pre-cursor solution before electrospinning. After pyrolysis the titania nanofibers supported and encapsulated the erbia particles. Temperature-dependent near-infrared emission spectra demonstrate that the erbia-containing nanofibers emit selectively in the range 6000–7000 cm−1. Because of their large surface to volume ratios and narrow-band optical emission, these nanofibers can be used as selective emitters for thermophotovoltaic applications

Erbia-modified Electrospun Titania Nanofibres for Selective Infrared Emitters

Tetraisopropyl titanate (TPT) was mixed with a solution of polyvinylpyrrolidone (PVP) and the solution electrospun into nanofibres. Thermal annealing at 900 °C was used to pyrolyse the PVP, leaving nanofibres of rutile-phase titania. Erbium (III) oxide particles were also added into the solution before electrospinning, and selectively modified the near-infrared optical properties of the titania nanofibres as verified by both absorption and emission spectra. We thereby demonstrate the production of high-temperature optically functionalized nanostructures that can be used in a thermophotovoltaic energy conversion system