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10Решетневские чтения
layer on a nanocrystal structure. An example of the emission spectrum of Cr3+ luminescence for nanocrystalline SrTiO3:Cr powder with the average particle size 5 nm is on the see figure. In this case, the R-line position was determined to be 789.4 nm at 11 K.
è 1.5-
I
8 i,o-
I
I 0,50,0770 780 790 800 810
wavelength [nm]
Emission spectrum of nanocrystalline SrTiO3:Cr (5 nm). Spectrum was recorded at 11 K
It seems that ferroelectric phase transition can appear in SrTiO3 particles with suitable shape and size. The study of the luminescence of Cr3+ impurity probe in nanocrystalline SrTiO3:Cr powders evidenced so far increasing instability towards a ferroelectric phase transition in small SrTiO3 nanoparticles with their size reduction and probably even the emergence of low-temperature ferroelectric phase transition in sufficiently small SrTiO3:Cr nanoparticles. The question requires further investigations nevertheless [2; 3].
References
1. Stokowski S. E., Schawlow A. L. // Phys. Rev. 178; 1969.
2. Trepakov V. A., Potucek Z., Makarova M. V. et al. // Nazev. Phys. Condens. Matter 21. 2009. P. 375303.
3. Potucek Z., Trepakov V. A., Makarova M. V. et al. // Nazev, Mat. Science and Technology 25, 2009. P. 11.
К. Драгунова
Чешский технический университет в Праге, Чешская Республика, Прага
ФОТОЛЮМИНЕСЦЕНЦИЯ НАНОКРИСТАЛЛИЧЕСКИХ СОЕДИНЕНИЯ SrTiO3
С ВКРАПЛЕНИЯМИ ХРОМА
Материалы с перовскитовой структурой (ABO3) находят широкое применение, благодаря их ферроэлек-трическим, пьезоэлектрическим и оптическим свойствам. Переходя от основных к нанокристаллическим материалам, свойства могут заметно изменяться из-за усиления свойств покрытия. По этой причине в настоящее время широко изучается применение нанокристаллических материалов. Представлен краткий обзор существующих исследований по фотолюминесценции нанокристаллических соединений SrTiO3 с вкраплениями хрома и по использованию ионов сг3+ в качестве спектроскопической пробы при исследовании фазовых переходов.
© Dragounova К., 2011
УДК 53
T. Koubsky
Czech Technical University, Faculty of Nuclear Research and Physical Engineering, Department of Solid State Engineering, Czech Republic, Prague
SIMULATION OF CHEMICAL STABILITY OF UAM-069 AND ONE OF THE DEGRADATION
PRODUCTS*
For nuclear hydrometallurgical separation process development, it is necessary to demonstrate the stability of the extracting systems. The m-xylylene-bis-diglycolamide (compound 1) is used in this process but its instability is undesirable. It is known that one of the degradation products (2) is significantly more stable while having comparable extraction properties. The simulation of chemical stability showed significantly less localized density of the HOMO for 2, which corresponds to the lower preference of the ether oxygen atom to be the weak point.
One of the strategies used for spent nuclear fuel management is the hydrometallurgical treatment of the high level liquid waste (HLLW). Among others, it comprises actinide and lanthanide group separation. In this process the compound 1 UAM-069 (m-xylylene-bis-diglycolamide - figure 1) is used for good selective properties of its diglycolamide group. The degradation of
1 in the radioactive and acidic environment leads clearly to undesirable effects caused by decrease of concentration. Unlike the other fragments, the major degradation product (2 - see figure 2) also acts as an efficient extractant but its stability against the hydrolysis is higher. The main reason of the degradation is an electrophilic (acidic) attack of hydrogen cations.
^Computational results obtained using software programs from Accelrys Software Inc. The ab initio calculations performed with the DMol3 program with the BLYP, PBE and RPBE xc-functionals.
HanoMamepuaxbi u Hanomexnoxoguu e aspoKocMuuecKpü ompacxu
The disociation to H+ ions is supported by the contact with highly radioactive solutions. As was concluded in [2], the prevalent hydrolysis leading to 2 takes place on ether groups (O(2)). Therefore our purpose is to simulate the stability of the ether atoms of 1 and 2 against the electrophilic attack and find the differences, as was observed experimentally [2].
Figure 1
f-(r) =
dp(r)
dN
V (r)
= lim
e®0+
Pn +e (r) -PN (r)
Here pN(r) is the electron density of the system of N electrons. The derivation is made at constant external potential V(r). The ESP is calculated at each point in space from the electron density p(r) in a standard way in the sense of Coulomb forces. The density of HOMO is calculated from the wavefunctions obtained from the DFT calculation of the system. Since the chemical hardness n (defined by Pearson, 1983) of both our compounds is high, according to [1], the primary indicator should be the ESP. From both the ESP and the Fukui function the "condensed" atomic values can be obtained by the Mullikan population analysis (MPA).
Now let's focus on the two compounds and let's investigate primarily the properties of the surroundings of the ether atoms. The results for the ESP volumetric data of 1 showed the belt of highly negative values between the three oxygen atoms (two carbonyl atoms and one
ether atom between them) which also corresponds to the values of local atomic charges (MPA) - see the table 1. The extreme charge is carried by the ether atom which corresponds to the observed high reactivity.
The MPA atomic charges of the first carbonyl, ether and second carbonyl (in elementary charge units e)
1 2
O(i) -0.465 -0.477
O(2) -0.486 -0.505
0(3) -0.478 -0.473
Figure 2
Our indicators of chemical reactivity (showing high probability of the electrophilic attack [1]) were the electrophilic Fukui function /", the negative values of electrostatic potential (ESP) and the location of HOMO (highest occupied molecular orbital). The theoretical platform for all our computation was the density functional theory (DFT) enhanced mainly by Hohenberg, Kohn and Sham in 1964 and 1965. (The quantum mechanical program DMol3 with the Accelrys Materials Studio software was used.) In the field of the DFT, the / Fukui function was defined by Yang and Parr (1984) as
As for the molecule 2, the results were unfortunately not substantially different. The ESP isosurface appeared to have less negative values in the surroundings of the ether atom but the MPA local charges showed even deeper extreme at the mentioned ether atom. Also the calculation of the Fukui function, being a secondary indicator, has not brought anything new. The maxima of the f "(r) volumetric data were located on the carbonyl oxygen atoms for both 1 and 2.
More interesting results were obtained from the calculation of HOMO. While on 1 it was localized in the area of the second carbonyl (O(3)) and the second amide, on 2 the HOMO was much more delocalized over all the molecule. The restricted location of HOMO on 1 could support the idea of the reactivity near the ether atom, but for 2 there is almost no place with higher concentration of the HOMO density. This fact cannot determine any location for the preferred reactivity and thus it could be interpreted as a sign of higher stability of 2.
We can conclude that, unfortunately, for the fragment 2 the results of the Fukui function and of the primary indicator ESP was nearly the same as for 1 and thus they contradicted the experiment. This excluded them as the reliable indicators. Only the shape of the HOMO (one of the secondary indicators) appeared much less localized then for the previous 1. This could refer to the lower reactivity of the experimentally discovered ether oxygen atom. Further research of the Fukui function interpretation and aso of the right reaction path of the decay could bring more reliable information [3; 4].
References
1. Anderson J. S. M., Melin, J., Ayers, P. W. Conceptual Density-Functional Theory for General Chemical Reactions, Including Those That Are Neither Charge- nor Frontier-Orbital-Controlled // J. of Chemical Theory and Computation. 2007. № 3(2). P. 358-374.
2. Galán H., Murillo, M. T., Sedano, R., Núñez, A., de Mendoza, J., González-Espartero, A., Prados, P. Hydrolysis and Radiation Stability of m-Xylylene Bis-diglycolamide: Synthesis and Quantitative Study of Degradation Products by HPLC-APCI+ // European Journal of Organic Chemistry. 2011.
3. Kalvoda L., Computer Simulation Study of Chemical Stability of UAM-069 // Report of the ACSEPT meeting. Manchester. 2011.
4. Martin R. M. Electronic Structure: Basic Theory and Practical Methods. Cambridge University Press. New York. 2004.
(Решетневскце чтения
Т. Кобский
Чешский технический университет, Чешская Республика, Прага
МОДЕЛИРОВАНИЕ ХИМИЧЕСКОЙ УСТОЙЧИВОСТИ УАМ-069 И ОДНОГО ИЗ ПРОДУКТОВ ЕГО РАСПАДА
Для развития процесса ядерного гидрометаллургического разделения необходимо продемонстрировать стабильность систем извлечения. В этом процессе используется соединение m-xylylene-bis-diglycolamide (соединение 1), но его неустойчивость является нежелательной характеристикой. Известно, что один из продуктов деструкции (2) значительно более устойчив и имеет сопоставимые свойства извлечения. Моделирование химической стабильности показало значительно менее ограниченную плотность HOMO для 2, что соответствует более низкому предпочтению кислородного атома эфира, расположенному в слабой позиции.
© Koubsky Т., 2011
УДК 53
I. Kraus
Czech Technical University, Czech Republic, Prague
SOLID STATE PHYSICS AT THE CZECH TECHNICAL UNIVERSITY IN PRAGUE
The contribution contains a brief description of the solid state physics research at the Faculty of Nuclear Sciences and Physical Engineering (FNSPE) of the Czech Technical Unversity in Prague.
There is no doubt that among all the fields of physics, solid state physics is dominant as far as the number of scientists is concerned for whom it has become their career, as well as the institutions which conduct experiments with solid state substances, search for theoretical explanations for their observed behaviour, and express hypotheses for their new properties. Solids are also unequalled in the number of journals accepting contributions in this field, the number of publications, and their use in real life.
Keeping in view the discoveries of the 20th century that have changed our lives from the very fundamentals (splitting of uranium, semiconductors, and the laser), two of them can be attributed to solid state physicists. The first discovery was made by Shockley-Bardeen-Brattain, a trinity of American physicists, towards the end of the 40's. They appeared on the Nobel Prize Winners' list in physics on December 10th, 1956, for investigations into semiconductors and the discovery of the transistor phenomenon. The second greatest discovery of the recent time is the laser (Light Amplification by Stimulated Emission of Radiation). Its parents are Charles Hard Townes, an American, and Nikolay Gennadievich Basov and Alexander Mikhailovich Prochorov, two Russians, Nobel laureates for 1964.
Czech Technical University in Prague included solid state physics into its programmes as early as autumn 1960. In the beginning, training was provided by three full-time members of staff of the Solid State Physics Section of the then Faculty of Technical and Nuclear Physics, and several dedicated part-timers; later a proper
department was founded, since 1967 known as the Department of Solid State Engineering. Its scientific activities was then defined by both the objektive factors (i. e., state of the art of the field), and the scientists leading the team of academic and technical staff. In the beginning, the research issues covered mainly the theory of solids, theory of magnetism, and technology of magnetic substances; later the attention shifted to research into semiconductor technology, semiconductor detectors, X-ray and neutron diffraction, optical properties of solids, nanotechnology, surface physics, polymer physics and materials simulations.
To those interested in studying physical engineering, the Faculty offers both courses of the „non-engineering" type (i. e. calculus and analysis, algebra, numerical mathematics and statistics, quantum mechanics, nuclear physics, crystallography, theory of solids, physics of metals and dielectrics), and the „engineering" type, e. g. applications of computer technology, superconductivity, applications of semiconductor electronics, semiconductor technology, semiconductor measurements methods of solids, experimental methods of X-ray and neutron diffraction, and others.
The first scientific achievement of note that brought the Department to the attention of peers was the theory of spontaneous magnetisation of thin ferromagnetic films and also the preparationn of layers by vakuum evaporation for ferromagnetic elements of the iron group and the lanthanides. Close cooperation with the Institute of Magnetic Substances in Jena also helped to develop the technology and fundamental magnetostatic masurements
