Search results for "solid"
showing 10 items of 3575 documents
Die polykondensation des p-kresoldialkohols
1952
Die Polykondensation (Hartung) des p-Kresoldialkohols, die in Platin- oder Silbergeraten ausgefuhrt wird, zeigt ubereinstimmenden Verlauf und ist abhangig von der Reinheit des p-Kresoldialkohols. Die Geschwindigkeit der Kondensation ist verschieden unter Luft und Stickstoff. Ebenso zeigt das Volumen der Schmelze bzw. deren Schichthohe einen Einflus auf die Hartungsgeschwindigkeit. Verfolgt man die Kondensation durch den Gewichtsverlust (in Verbindung mit Formaldehydbestimmungen), so ist die Trocknung der Kondensate besonders zu beachten; der Trocknungsverlust nach der Kondensation kann den Gewichtsverlust unmittelbar nach der Hartung erreichen. Bei Einhalten der angegebenen Kondensationsbed…
Structure and transport properties of amorphous aluminium silicates: computer simulation studies
2005
The structure and transport properties of SiO2-Al2O3 melts containing 13 mol% and 47 mol% Al2O3 are investigated by means of large scale molecular dynamics computer simulations. The interactions between the atoms are modelled by a pair potential which is a modified version of the one proposed by Kramer et al. [J. Am. Chem. Soc. 64, 6435 (1991)]. Fully equilibrated melts in the temperature range 6000 K >= T > 2000 K are considered as well as glass configurations, that were obtained by a rapid quench from the lowest melt temperatures. Each system is simulated at two different densities in order to study the effect of pressure on structural and dynamic properties. We find that the Al ato…
Evidence of nickel ions dimerization in NiWO$_4$ and NiWO$_4$-ZnWO$_4$ solid solutions probed by EXAFS spectroscopy and reverse Monte Carlo simulatio…
2021
G.B. acknowledges the financial support provided by the State Education Development Agency for project No.1.1.1.2/VIAA/3/19/444 (agreement No. 1.1.1.2/16/I/001) realized at the Institute of Solid State Physics, University of Latvia. A.K. and A.K. would like to thank the support of the Latvian Council of Science project No. lzp-2019/1-0071. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.
Pressure effects on the structural and electronic properties of ABX4 scintillating crystals
2008
Studies at high pressures and temperatures are helpful for understanding the physical properties of the solid state, including such classes of materials as, metals, semiconductors, superconductors, or minerals. In particular, the phase behaviour of ABX4 scintillating materials is a challenging problem with many implications for other fields including technological applications and Earth and planetary sciences. A great progress has been done in the last years in the study of the pressure-effects on the structural and electronic properties of these compounds. In particular, the high-pressure structural sequence followed by these compounds seems now to be better understood thanks to recent exp…
Peculiarities of the local structure in new medium- and high-entropy, low-symmetry tungstates
2022
G. Bakradze acknowledges financial support provided by the Latvian Council of Science for project no. 1.1.1.2/VIAA/3/19/444 (agreement no. 1.1.1.2/16/I/001) realized at the Institute of Solid State Physics, University of Latvia. The Institute of Solid State Physics, University of Latvia, as a centre of excellence, has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement no. 739508, project CAMART2.
Chemical-state analyses of Ni, Zn, and W ions in NiWO$_4$-ZnWO$_4$ solid solutions by X-ray photoelectron spectroscopy
2022
The chemical states of Ni, Zn, and W in microcrystalline NiWO$_4$-ZnWO$_4$ solid solutions were studied by X-ray photoelectron spectroscopy. The recorded spectra of the Ni 2p, Zn 2p, and W 4f photoelectron lines and Ni L$_2$M$_{23}$M$_{45}$, Zn L$_3$M$_{45}$M$_{45}$, and W N$_4$N$_{67}$N$_{7}$ Auger-transition lines show pronounced changes with increasing Zn concentration. The positions of the resolved photoelectron and Auger-transition lines were combined to construct so-called chemical-state plots (Wagner or Auger-parameter plots) for metal ions in solid solutions. With increasing Zn concentration, the Auger parameter increases for Ni and decreases for W, thus evidencing a lowering and an…
Evidence of delocalized excitons in amorphous solids
2010
We studied the temperature dependence of the absorption coefficient of amorphous ${\mathrm{SiO}}_{2}$ in the range from 8 to 17.5 eV obtained by Kramers-Kronig dispersion analysis of reflectivity spectra. We demonstrate the main excitonic resonance at 10.4 eV to feature a close Lorentzian shape redshifting with increasing temperature. This provides a strong evidence of excitons being delocalized notwithstanding the structural disorder intrinsic to amorphous ${\mathrm{SiO}}_{2}$. Excitons turn out to be coupled to an average phonon mode of 83 meV energy.
Quantum-well states in ultrathin Ag(111) films deposited onto H-passivated Si(111)-(1x1) surfaces
2002
Ag(111) films were deposited at room temperature onto H-passivated Si(111)-(1x1) substrates, and subsequently annealed at 300 C. An abrupt non-reactive Ag/Si interface is formed, and very uniform non-strained Ag(111) films of 6-12 monolayers have been grown. Angle resolved photoemission spectroscopy has been used to study the valence band electronic properties of these films. Well-defined Ag sp quantum-well states (QWS) have been observed at discrete energies between 0.5-2eV below the Fermi level, and their dispersions have been measured along the GammaK, GammaMM'and GammaL symmetry directions. QWS show a parabolic bidimensional dispersion, with in-plane effective mass of 0.38-0.50mo, along…
Recent progress on the characterization of the high-pressure behaviour of AVO4 orthovanadates
2018
AVO4 vanadates are materials of technological importance due to their variety of functional properties. They have applications as scintillators, thermophosphors, photocatalysts, cathodoluminescence, and laser-host materials. Studies at HP-HT are helpful for understanding the physical properties of the solid state, in special, the phase behavior of AVO4 materials. For instance, they have contributed to understand the macroscopic properties of vanadates in terms of microscopic mechanisms. A great progress has been made in the last decade towards the study of the pressure-effects on the structural, vibrational, and electronic properties of AVO4 compounds. Thanks to the combination of experimen…
Hydrogen-related conversion processes of Ge-related point defects in silica triggered by UV laser irradiation
2005
The conversion processes of Ge-related point defects triggered in amorphous SiO2 by 4.7eV laser exposure were investigated. Our study has focused on the interplay between the (=Ge•-H) H(II) center and the twofold coordinated Ge defect (=Ge••). The former is generated in the post-irradiation stage, while the latter decays both during and after exposure. The post-irradiation decay kinetics of =Ge•• is isolated and found to be anti-correlated to the growth of H(II), at least at short times. From this finding it is suggested that both processes are due to trapping of radiolytic H0 at the diamagnetic defect site. Furthermore, the anti-correlated behavior is preserve…