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Development of crystal structure of (Er,Lu)2(Ti,Zr)2O7 materials
Zelenka, Jiří ; Klicpera, Milan (advisor) ; Kaštil, Jiří (referee)
The present thesis is focused on the development of a crystal structure of A2B2O7 materials, where A is a rare-earth element and B is a transition metal. These materials crystalize generally in four crystallography structures. The thesis is focused on structural transitions from an ordered cubic structure, so-called pyrochlore structure, to a fully disordered cubic structure, so-called defect- fluorite structure, to semi-ordered rhombohedral structure. Compared to previous studies, which dealt with these structural changes in A2Zr2O7 with the substitution of the rare-earth element, this thesis is focused on evolution of structure with a substitution on the B positions. For this research of the crystal structure evolution two series of oxides, Er2(Ti,Zr)2O7 and Lu2(Ti,Zr)2O7, have been selected. Twenty-one samples of those series were prepared by the floating zone method and Czochralski method. Analysis of prepared crystals was performed by using the Laue diffraction method and the powder diffraction methods. For the study, X-ray and neutron diffraction were utilized. A quality of the prepared materials and their crystal structure were studied with the respect to a concentration of Ti-Zr. The development of the crystal structure has been discussed. The thesis will serve as a ground for following research of...
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Magnetocaloric properties of rare-earth compounds
Kaštil, Jiří ; Javorský, Pavel (advisor) ; Kolomiets, Alexander (referee) ; Solzi, Massimo (referee)
This work presents study of magnetocaloric properties of compounds exhibiting unusual magnetic characteristics. Several systems were studied: TbNiAl, (Tb,Y)NiAl, TbNi(Al,In), TbFeAl, GdFeAl, Ni2MnGa based compounds and amorphous metallic alloy Gd-Co-Al-Y. Influence of magneto-crystalline anisotropy on magnetocaloric effect was studied on singlecrystalline sample of TbNiAl compound. The maximum of entropy change was measured with orientation of magnetic field along c axis and compared to polycrystalline sample a 100% increase was observed. Substitutions of Y and In in TbNiAl led to a change of magnetic ordering. Both substitution led to increase of RCP values of studied material. TbFeAl and GdFeAl compounds, characterized by partial disorder of Fe and Al atoms, showed magnetocaloric effect in wide temperature region which led to interesting values of RCP~350 J kg-1 . Very broad region of magnetocaloric effect was also observed on amorphous metallic material of Gd-Co-Al-Y. The effect of Er substitution in Ni2MnGa based compound on its magneto-structural transition, connected with inverse magnetocaloric effect, was studied. The direct measurement method of adiabatic temperature change is described and instrument for such measurement, developed in collaboration with FZU AVČR, v.v.i., is presented.
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Vliv substitucí na magnetokalorický jev u vybraných sloučenin vzácných zemin
Kaštil, Jiří
The anisotropy of the magnetocaloric effect was studied on DyNiAl single crystal. Our data reveal a strong anisotropy of the magnetocaloric effect. The large effect occurs for field applied along the c-axis whereas the entropy change is small for the perpendicular field direction. The influence of substitution on the magnetocaloric effect was measured in the Gd(Co1-xRhx)2 compounds (where x was from 0.05 to 0.30) and Dy(Co1-xFex)2 compounds (where x was from 0.00 to 0.03). The substitution of Co by Rh leads to a decrease of the transition temperature, Tc, and increase of the maximum entropy change. The Tc increases but the maximum of entropy change quickly decreases in case of Fe substitution. The last studied systems were the Gd1-xTbx alloys with x in range from 0.00 to 0.40. The influence of the sample shape and orientation was studied. The thin ribbon oriented along the magnetic filed gave the highest value of the entropy change. The three measurement techniques were used: the heat capacity measurement, the magnetization measurement and the direct measurement of the temperature change.
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Compressibility of an intermetallic compound
Staško, Daniel ; Prchal, Jiří (advisor) ; Kaštil, Jiří (referee)
Title: Compressibility of an intermetallic compound Author: Daniel Staško Department: Department of Condensed Matter Physics Supervisor: RNDr. Jiří Prchal, Ph.D., Department of condensed matter physics Abstract: This work focuses on the method of using miniature strain gages for the measurement of volume change and strain in hydrostatic pressure. Two state variables are involved in the changes - temperature and pressure. A copper reference material was used to determine the pressure and temperature corrections for the specific type of strain gage used it this work. To demonstrate this method, a pressure dependence of strain was measured up to 2.3GPa for the CeCuAl3 single crystalline sample along particular crystallographic directions. It is studied for its interesting magnetic properties and this work aims to contribute to its complex study. Temperature dependencies of strain under low and high pressure were also measured. Keywords: high pressure, compressibility, strain gage, CeCuAl3
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Magnetocaloric properties of rare-earth compounds
Kaštil, Jiří ; Javorský, Pavel (advisor) ; Kolomiets, Alexander (referee) ; Solzi, Massimo (referee)
This work presents study of magnetocaloric properties of compounds exhibiting unusual magnetic characteristics. Several systems were studied: TbNiAl, (Tb,Y)NiAl, TbNi(Al,In), TbFeAl, GdFeAl, Ni2MnGa based compounds and amorphous metallic alloy Gd-Co-Al-Y. Influence of magneto-crystalline anisotropy on magnetocaloric effect was studied on singlecrystalline sample of TbNiAl compound. The maximum of entropy change was measured with orientation of magnetic field along c axis and compared to polycrystalline sample a 100% increase was observed. Substitutions of Y and In in TbNiAl led to a change of magnetic ordering. Both substitution led to increase of RCP values of studied material. TbFeAl and GdFeAl compounds, characterized by partial disorder of Fe and Al atoms, showed magnetocaloric effect in wide temperature region which led to interesting values of RCP~350 J kg-1 . Very broad region of magnetocaloric effect was also observed on amorphous metallic material of Gd-Co-Al-Y. The effect of Er substitution in Ni2MnGa based compound on its magneto-structural transition, connected with inverse magnetocaloric effect, was studied. The direct measurement method of adiabatic temperature change is described and instrument for such measurement, developed in collaboration with FZU AVČR, v.v.i., is presented.
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Vliv substitucí na magnetokalorický jev u vybraných sloučenin vzácných zemin
Kaštil, Jiří
The anisotropy of the magnetocaloric effect was studied on DyNiAl single crystal. Our data reveal a strong anisotropy of the magnetocaloric effect. The large effect occurs for field applied along the c-axis whereas the entropy change is small for the perpendicular field direction. The influence of substitution on the magnetocaloric effect was measured in the Gd(Co1-xRhx)2 compounds (where x was from 0.05 to 0.30) and Dy(Co1-xFex)2 compounds (where x was from 0.00 to 0.03). The substitution of Co by Rh leads to a decrease of the transition temperature, Tc, and increase of the maximum entropy change. The Tc increases but the maximum of entropy change quickly decreases in case of Fe substitution. The last studied systems were the Gd1-xTbx alloys with x in range from 0.00 to 0.40. The influence of the sample shape and orientation was studied. The thin ribbon oriented along the magnetic filed gave the highest value of the entropy change. The three measurement techniques were used: the heat capacity measurement, the magnetization measurement and the direct measurement of the temperature change.
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The influence of substitutions on the magnetocalloric effect in selected rare-earth compounds
Kaštil, Jiří ; Javorský, Pavel (advisor) ; Svoboda, Pavel (referee)
The anisotropy of the magnetocaloric effect was studied on DyNiAl single crystal. Our data reveal a strong anisotropy of the magnetocaloric effect. The large effect occurs for field applied along the c-axis whereas the entropy change is small for the perpendicular field direction. The influence of substitution on the magnetocaloric effect was measured in the Gd(Co1-xRhx)2 compounds (where x was from 0.05 to 0.30) and Dy(Co1-xFex)2 compounds (where x was from 0.00 to 0.03). The substitution of Co by Rh leads to a decrease of the transition temperature, Tc, and increase of the maximum entropy change. The Tc increases but the maximum of entropy change quickly decreases in case of Fe substitution. The last studied systems were the Gd1-xTbx alloys with x in range from 0.00 to 0.40. The influence of the sample shape and orientation was studied. The thin ribbon oriented along the magnetic filed gave the highest value of the entropy change. The three measurement techniques were used: the heat capacity measurement, the magnetization measurement and the direct measurement of the temperature change.
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