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11CHEMICAL SCIENCES | ХИМИЧЕСКИЕ НАУКИ
THE COMPOSITE CONTAINING NANOSIZED FEF3 AND CRF3, ALUMINUM
COMPOUND, AND CARBON COMPONENTS SYNTHESIZED IN PULSE HIGH-VOLTAGE DISCHARGE PLASMA AND ITS MAGNETIC PROPERTIES
Kuryavyi V.G.
Tkachenko I.A.
Utfinov A.Yu.
Bouznik VM.
Intfitute of Chemitfry, Far-Eatfern Branch, Russian Academy of Sciences
159, Vladivostok, Russia
ABSTRACT
Nanocomposites containing nanosized FeF3 and CrF3 particles, aluminum compound and carbon components have been synthesized by a method employing a combined detraction of electrodes containing Fe, Cr, Al, and Fluoroplafl in the plasma of pulse high-voltage discharge in air. Particles having complex shapes of a size of 20-400 nm have been obtained. Upon annealing at 800°C, the samples contained nanocryflalline hematite and Cr and Al oxides. The samples magnetic properties were fludied on a SQUID magnetometer in the temperature range 300-2 K. The samples are hard-magnetic. The non-annealed sample contains single-domain particles with different magnetic moment blocking temperatures (up to 300 K) having heterogeneous magnetic flructures. The non-annealed sample contains nanocryflalline hematite without Morin transition, around 50 K the particles magnetic flructure undergoes some changes.
Keywords: plasma chemiflry, nanocryflals, iron fluoride, chromium fluoride, iron oxide, chromium oxide, magnetic nanoparti-cles, magnetic properties.
1. Introduction
Materials containing magnetic nanoparticles are of interefl due to the fact that they could manifefl a number of specific properties, for example, superparamagnetism, magnetic moment tunneling, extra high magnetic resiflance, and anomalously high magnetocalorimetric effect, whereas the particle size and magnetic flructure affect the density of recording on magnetic media, coercive force of the magnetic material, ability for shielding the electromagnetic radiation etc. [1-3]. In complex composites, one could observe magnetoelectric effects [4]. In the present work, a simple method, which enables one to obtain nanocomposites containing magnetic nanoparticles of different sizes and having complex morphological and magnetic flructures and compositions, was applied [5, 6]. The combined detraction of iron-containing electrodes and Fluoroplafl in the pulse high-voltage discharge plasma was used. A nanocomposite containing nanosized FeF3, CrF3, aluminum compound Al, and carbon component has been obtained.
2. Experimental Setup
The samples morphology was fludied by the methods of scanning electron microscopy (SEM) on a Hitachi S5500 scanning electron microscope (Japan) and a Libra 200FE transmission electron microscope (TEM) (Carl Zeiss, Germany). The sample sputtering was not applied. The local energy-dispersive spectroscopy data were obtained on a Thermo Scientific (USA) spectrometer. The X-ray diffraction analysis (XRD) was carried out on a D8 ADVANCE diffractometer (Bruker, Germany). The X-ray photoelectron spectroscopy fludy was performed on a SPECS device (Germany). The MgKa
radiation was used for spectra excitation. The samples magnetic characteriflics were measured using a MPMS-XL-5 SQUID-magnetometer (Quantum Design, USA).
3. Sample Synthesis
Samples were fabricated by the combined detraction of electrodes, containing Fe (61.9%), C (8.6%), O(8.2%), Al (3.5%), Si (0.7)%, Cr (16.6%), Mn (0.5%), and polytetrafluoroethylene of the grade F-4 ('Fluoroplafl') in the plasma of pulse highvoltage discharge initiated in a gaseous medium [5, 6]. The experiment was carried out as follows: electrodes of a diameter of 1 mm pulled apart at a diflance of about 3 mm underwent application of pulse high voltage of amplitude of 9 kV, pulse duration of 100 ^s, and frequency of 2000 Hz. Upon voltage switching-on, a plasma filament emerged between the electrodes. Here, no visible product emission from the plasma filament area was observed. Thereafter, Fluoroplafl was placed into plasma. A Fluoroplafl rod of a cross-section size of 3*3 cm2 was moved into plasma gradually in the process of combuflion of the rod end. Under these conditions, Fluoroplafl and the material of electrodes in contact with plasma are actively detracted with formation of light-brown smoke in the plasma area. Smoke deposited on the subflrate plate made of quartz glass. The deposited subflance was collected from the subflrate plate by scraping and invefligated. Electrodes were placed in an exhaufl hood in open air; the subflrate plate for sample collection was placed above the plasma area at a diflance of 3 cm.
4. Results and Discussion
Powder of light-brown color was obtained (sample 1). As indicated by SEM and TEM data, it consifls of particles of a size of 20-400 nm (Fig. la) of a complex structure - see Figs, lbcd.
S5500 10.0kV -0.2mm x70.0k SE 7/28/2014 18:03
Fig. 1. SEM (a, b) and TEM (c, d) images of the sample 1.
The particles look like porous cryflallites that are coated or fully filled with smaller nanoparticles of a size of 5-10 nm and some amorphous subflances. The TEM data (Fig. 1d) allow assuming that nanoparitcles of a size of 5-10 nm are nanocryflals, since one can see their faces and cryflal planes.
The XRD analysis data indicate to the presence of FeF3 cryflalline phases. The data of local energy-dispersive spectroscopy (Table 1, Fig. 2) indicate to the presence of C, O, F, Al, Cr, and Fe.
Table 1.
EDS data.
Element,Line Line Content, at. %,in total bulk Content, at. %,in crystallite Error, at. %,
C K 14.9 33.6 ± 1.3
O K 14.8 - ± 0.5
F K 46.8 34.3 ± 1.5
Al K 0.9 0.9 ± 0.1
Si K 0.5 - ± 0.1
Cr K 4.1 1.8 ± 0.4
Fe L 11.7 10.2 ± 3.5
Cu(Substrate signal) L 6.3 19.2 ± 0.5
Fig. 2. SEM images of the sample 1, circles show the areas of EDS analysis.
Measurements were carried out for total sample bulk (Fig. It is observed that in all the cases the iron content is more than 2a) and directly in cryflallites (Fig. 2b). The element contents threefold higher than that of chromium. That is cryflallite is a directly in cryflallites were measured in particles located composite of compounds of chrome and iron. separately from the sample total bulk, at a diflance of more than The sample XPS spectra contain the lines of C, O, F, Cr, and 2 micron, in order not to regifler the EDS signal from total bulk. Fe; the spectra parameters are shown in Table 2.
Table 2.
XPS data of the sample 1.
Type of core electrons Eb., eV Content, at. %, experiment 1 Content, at. %, experiment 2 Bond type, point 2
Fe 2p 715.3 1.2 0.2 FeF3
Cr 2p 579.3 11.3 11.0 CrF3
F 1s 689.2 - 4.4 CF2
F 1s 684.9 51.1 29.4 CrF3
O 1s 533.3 16.0 16.0 OF, OH
O 1s 531.3 16.3 12.1 CrOx, FeOx
C 1s 292.0 - 1.6 CF2
C 1s 288.0 - 4.0 CO, CF
C 1s 285.0 4.2 21.3 CH
According to the XPS data, in the sample chromium is contained as CrF3 and, iron - as FeF3, carbon is moflly of the aliphatic nature, although fluorinated or oxidized carbon is also available. Different syntheses approaches correspond to different relative contents of various carbon components as well as iron and chromium. In all measurements, the iron/chromium contents ratio was less than 1, the maximal value was 0.3. Such low iron content regiflered by the XPS method contradicts EDS and XRD data. This contradiction can be eliminated, if one assumes that the Fe-containing subflance particles are coated with a sufficiently thick layer of Cr compounds, taking into account a small depth of the XPS analysis (about 1-2 nm).
Based on the data of SEM, TEM, XRD, and XPS, one can assume that chromium compounds are present as nanoparticles of chromium fluoride of a sizes some nanometers, which densely coat larger nanoparticles continuing iron fluorides. The absence of chromium fluorides lines in XRD spectra can be explained by their broadening related to small sizes of cryflallites [7] or to the subflance amorphous flate.
Figure 3 shows temperature dependencies of the sample magnetization (M) obtained using ZFC and FC techniques. Figure 4 shoes these values dependencies on the magnetic field intensity recorded at 3 and 300 K.
0.5
J? E
CD
0.4-
0.3
0.2
1 1 1 .....■......^C ' 1 H=100 Oe
/
0
100
200
300 T (K)
Fig. 3. Temperature dependencies of the sample 1 magnetization.
E 0
<t>
-2
-4
T=3 K Hc= - 1184/4860e I 1
T = 300 K - Hc=-130/130 Oe
-50000 -30000 -10000 10000 30000 50t)00 -50000 -30000 -10000 10000 30000 50000 H (Oe) H (Oe)
Fig. 4. Temperature dependencies of the sample 1 magnetization on the intensity of the external magnetic field at different temperatures.
The observed maximum on the ZFC curve and temperature indicate to the fact that the sample contains single-domain hyfleresis of ZFC and FC curves (Fig. 3) and the absence of particles that are transformed into a quasi-Sable Sate below the saturation on magnetization field dependencies (Fig. 4) could blocking temperature (Tb) [8].
300 T(K)
Fig. 5. TEM image (a) and magnetization temperature dependence (b) of the sample 2.
The maximum on the ZFC curve is flretched in a broad temperature range, which can demonflrate a broad range in sizes and in the blocking temperatures of particles forming the sample [9]. The latter assumption is corroborated by the microscopy data (Fig. 1). The reason of the exigence of hyfleresis on the magnetization field dependence at room temperature could
consifl in the presence of big size particles in the sample that are ferromagnetic at this temperature.
A subflantial shift of the hyfleresis low-temperature loop to negative fields indicates to the presence of exchange bias of the type antiferromagnetic-ferromagnetic/ferrimagnetic type (AFM-FM/FerriM) in the sample [10]. This fact is in
agreement with the earlier obtained data on a complex flructure of cryflallites.
Another feature of the obtained magnetic hyfleresis loops consifls in their 'waifl loop' shape. The latter is also the proof of the formation of a complex magnetic flate in the sample and can be the result of effects of magnetic anisotropy of single-domain particles [11], the simultaneous presence of single-domain and multi-domain magnetic particles [12], and switching between domains having different coercive forces [13]. The values of the coercive force of the obtained sample correspond to a hard magnetic material.
As follows from general analysis of SEM, TEM, EDS, XRD, XPS, and SQUID data, the obtained subflance comprises a material containing nanocomposite cryflallites of a size of less than 20-400 nm including single-domain magnetic nanoparticles with FeF3 and CrF3 as well as aluminum compounds and carbon component. At different temperatures, nanoparticles of different size are transformed into the superparamagentic flate.
The sample was fludied upon its annealing at 800°C for 2 h in air (sample 2). The data of XRD analysis indicate to the presence of cryflalline phases of hematite (a-Fe2O3) only. Particles of the sample 2 comprise cryflallites composed of nanoparticles of a size of less than 20 nm or individual nanoparticles (Fig. 5a).). According to the EDS data, the sample contains Fe (21.3 at. %), Cr (2.4 at. %), Al (1.2 at. %), O (35.7 at. %), and C (39.4 at. %). Measurements performed on individual cryflallites showed the presence of the same elements as in total bulk: Fe (15.4 at. %), Cr (1.3 at. %), Al (0.7 at. %), O (24.6 at. %), and C (58.0 at. %). According to the XPS data, the sample contains iron bound to oxygen (15.4 at. %), chromium bound to oxygen (10 at. %), oxygen bound to metals (67.1 at. %), and aliphatic carbon (7.5 at. %). Figure 5b shows the results of fludies of the temperature dependence of the sample magnetization. As follows from the presented data, the curve does not show the Morin transition characteriAic for hematite [14]. The temperature of Morin transition is known [15, 16] to be affected by such factors as small particle size and the presence of impurities in the ample under fludy. These factors can completely suppress the Morin transition and are present in the sample under fludy as well.
One should mention magnetization flepwise changes in the range 75-20 K. This range is known [17] to contain a peak resulting from the presence of adsorbed oxygen. However, in our case, the peak is broader than for the case of earlier obtained hematite with the Morin transition [18], and cover a broader temperature range - about 50 K inflead of 10 K. Mofl probably, there occurs juxtaposition of several effects so that extra fludies are required to obtain more reliable explanation of the magnetization increase.
5. Conclusions
A nanocomposite containing complex nanosized cryflallites composed of nanoparticles based on iron and chromium fluoride compounds and aluminum and carbon components has been synthesized by means of the method of combined detraction of metal electrodes and PTFE. Cryflallites have complex flructure and various sizes. At different temperatures, nanoparticles of different size are transformed into the superparamagentic flate. At different temperatures they are transformed into superparamagentic flate. The interaction between FM and AFM/ FerriM components takes place. Upon the sample annealing, the material containing nanocryflalline hematite, in which the Morin transition is absent, was obtained. The used synthesis methods are promising in fabrication of nanosized particles of
complex morphological and chemical fractures composed of even smaller nanoparticles of oxides or fluorides of different metals and capable to manifefl nanosized effects.
Acknowledgements
The authors are grateful to the Center of Microscopy of the Inflitute of Marine Biology FEBRAS for the opportunity to use the Libra 200 FE transmission electron microscope in this work.
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ИССЛЕДОВАНИЕ ОПТИЧЕСКИХ СВОЙСТВ ПОЛИГЕТЕРОАРИЛЕНОВ ДЛЯ АТИВНЫХ СЛОЁВ СОЛНЕЧНЫХ БАТАРЕЙ НА ГЕТЕРОПЕРЕХОДЕ
Пономарев И.И.
Скупов К.М. Разоренов Д.Ю. Пономарев Ив.И. Волкова Ю.А.
Институт элементоорганических соединений им. А.Н. Несмеянова РАН, Москва
Емец В.В.
Институт физической химии и электрохимии им. А.Н. Фрумкина РАН, Москва,
Десятов А.В. Саранин Д.С.
Российский химико-технологический университет им. Д.И. Менделеева. Москва INVESTIGATION OF POLYHETEROARYLENE OPTICAL PROPERTIES FOR HETEROJUNCTION SOLAR CELL ACTIVE LAYERS Ponomarev I.I. Skupov K.M. Razorenov D.Yu. Ponomarev Iv.I.
Volkova Yu.A. Russian Academy of Sciences A.N. Nesmeyanov Institute of Organoelement Compounds, Moscow, Russia Emets V.V., Russian Academy of Sciences A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Moscow, Russia Desyatov A.V.
Saranin D.S. D.I. Mendeleyev University of Chemical Technology of Russia АННОТАЦИЯ
Впервые исследованы оптические свойства полигетероариленов, содержащих конденсированные гетероциклы, применительно к возможности их использования в активных слоях солнечных батарей на гетеропереходе. Показано, что полимеры данного типа являются узкозонными полупроводниками n-типа и могут быть использованы как акцепторы в комбинации с фуллеренами. ABSTRACT
Optical properties of polyheteroarylenes containing condensed heterocycles were invefligated for the fir& time with regard to bulk heterojunction solar cell. It was shown that they are n-type low bandgap polymer semiconductors and can be used in combination with electron-accepting fullerenes for active layer design.
Ключевые слова: полигетероарилены, оптические свойства, солнечные батареи, гетеропереход Keywords: polyheteroarylenes, optical properties, bulk heterojunction solar cell
Введение
Многие исследуемые в настоящее время оптически активные полимерные материалы имеют такие недостатки, как узкая область поглощения света, низкая мобильность носителей заряда, а также низкие светостойкость и термическая стабильность, ограничивающие их практическое применение в солнечных элементах. В соответствии с недавними обзорами политиофены, наиболее применимый класс полимеров в области СЭ, широко изучаемый в течение последнего десятилетия, достигли пределов возможной эффективности. Для развития направления нужно исследовать новые классы сопряженных полимеров с более широким спектром поглощения и высокой стабильностью с целью установления фундаментальной взаимосвязи «структура-свойства» полисопряженных макромолекул, в частности, их оптической активности, зон фотопроводимости,
определяющих применение таких полимеров в различных областях электроники и оптоэлектроники, а именно, в солнечных батареях, активных слоях светоиспускающих диодов, в дисплеях и нелинейно-оптических устройствах.
Наиболее широко представленные в современной литературе полиарилены, полиариленвинилены, полиариленэ-тинилены, политиофены, полипирролы являются наиболее распространенными объектами для такого изучения и использования, однако получение этих полимеров с регулярной структурой, с достаточно высокими молекулярными массами и одновременно растворимыми в органических растворителях, т.е. перерабатывемыми, представляется трудноразрешимой задачей [1-5].
Лестничные и частично-лестничные гетероциклические полимеры представляют значительный интерес в качестве объектов исследования пленок и покрытий на их основе,
