Search

Your search keyword '"Daniš, S."' showing total 179 results
Start Over Author "Daniš, S."
179 results on '"Daniš, S."'

3. Physics of Polymorphic Transitions in CeRuSn

Author

Fikáček, J., Prokleška, J., Míšek, M., Custers, J., Daniš, S., Prchal, J., Sechovský, V., and Císařová, I.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We report a detailed study of the polymorphic transitions in ternary stannide CeRuSn on high quality single crystals through a combination of X-ray diffraction experiments conducted at 300, 275 and 120 K, and measurements of the thermal expansion, magnetization, and resistivity, along main crystallographic axes. In addition, the transition was followed as a function of pressure up to 0.8 GPa. The present X-ray diffraction data show that the room temperature polymorph consists of the lattice doubled along the c axis with respect to the CeCoAl-type structure consistent with previous reports. Upon cooling, the compound undergoes two successive transitions, first to a quintuple (290 K) and than to a triple CeCoAl superstructure at 225 K. The transitions are accompanied by a tremendous volume change due to a strong shrinking of the lattice along the c axis, which is clearly observed in thermal expansion. We advance arguments that the volume collapse originates from an increasing number of crystallographically inequivalent Ce sites and the change of ratio between the short and long Ce-Ru bonds. The observed properties of the polymorphic transition in CeRuSn are reminiscent of the transition in elementary Cerium, suggesting that similar physics, i.e., a Kondo influenced transition and strong lattice vibrations might be the driving forces.

Published
2012
Full Text
View/download PDF

22. The Effect of Niobium and Carbon on the Oxidation Resistance of Alloys Based on Fe3Al at 900°C.

Author

Hotař, A., Hotař, V., Švec, M., and Daniš, S.

Subjects
NIOBIUM, LAVES phases (Metallurgy), OXIDATION, FRACTAL dimensions, LEAD alloys, OXIDATION kinetics
Abstract

The cyclic oxidation behaviour of Fe-26Al-3Nb, Fe-27Al-5Nb and Fe-26Al-5Nb-1.4C (in at%) was investigated at 900°C. Chemical and phase analyses of the scale and oxide protrusions were conducted using light optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. The oxidation resistance of the tested alloys was determined using fractal dimension, and the results were compared with Fe-26Al-0.3Zr, Fe-26Al-1Zr (at%) and EN X5CrNi18-10 steel. The oxidation kinetics of Fe-26Al-3Nb and Fe-27Al-5Nb follow the parabolic rate law. Oxidation ingress into the alloys was observed due to the preferential oxidation of niobium-rich precipitates. Therefore, the oxidation rate of tested alloys increased with increasing amounts of particles of Laves phase (Fe, Al)2Nb and NbC. The niobium carbides oxidised more readily than the particles of Laves phase (Fe, Al)2Nb. The cyclic oxidation of Fe-Al-Nb and Fe-Al-Nb-C alloys at 900°C led to the formation of oxide scales composed of Al2O3, Fe2O3 and AlNbO4 (or non-stoichiometric AlNbO4). [ABSTRACT FROM AUTHOR]

Published
2022
Full Text
View/download PDF

40. Defect studies of ZnO single crystals electrochemically doped with hydrogen.

Author

Čížek, J., Žaludová, N., Vlach, M., Daniš, S., Kuriplach, J., Procházka, I., Brauer, G., Anwand, W., Grambole, D., Skorupa, W., Gemma, R., Kirchheim, R., and Pundt, A.

Subjects
CRYSTAL growth, HYDROGEN, ZINC oxide, CRYSTALS, POSITRONS
Abstract

Various defect studies of hydrothermally grown (0001) oriented ZnO crystals electrochemically doped with hydrogen are presented. The hydrogen content in the crystals is determined by nuclear reaction analysis and it is found that already 0.3 at. % H exists in chemically bound form in the virgin ZnO crystals. A single positron lifetime of 182 ps is detected in the virgin crystals and attributed to saturated positron trapping at Zn vacancies surrounded by hydrogen atoms. It is demonstrated that a very high amount of hydrogen (up to ∼30 at. %) can be introduced into the crystals by electrochemical doping. More than half of this amount is chemically bound, i.e., incorporated into the ZnO crystal lattice. This drastic increase of the hydrogen concentration is of marginal impact on the measured positron lifetime, whereas a contribution of positrons annihilated by electrons belonging to O–H bonds formed in the hydrogen doped crystal is found in coincidence Doppler broadening spectra. The formation of hexagonal shape pyramids on the surface of the hydrogen doped crystals by optical microscopy is observed and discussed. [ABSTRACT FROM AUTHOR]

Published
2008
Full Text
View/download PDF

47. High Temperature Study on Er2Ti2O7 Single Crystal.

Author

VLÁŠKOVÁ, K., VONDRÁČKOVÁ, B., DANIŠ, S., and KLICPERA, M.

Subjects
SINGLE crystals, ERBIUM, HIGH temperatures, CRYSTAL symmetry, X-ray powder diffraction, DIFFERENTIAL scanning calorimetry
Abstract

We present high temperature thermodynamical properties of a newly prepared Er2Ti2O7 single crystal investigated by means of dilatometry and differential scanning calorimetry measurements. Measured data are dominated by a wide anomaly between 1250 K and 1540 K. The high-temperature powder X-ray diffraction experiment subsequently demonstrates the anomaly to be related to changes within the pyrochlore lattice, however, preserving the crystal symmetry in the whole temperature range. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results