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Low-Loss Microwave Dielectrics for Different Frequency Ranges

100%
Belous A., Ovchar O.
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issue 1
221-227
EN
Depending on the operating frequency range of modern communication systems various microwave elements are required for effective operation of radio equipment. In this work potential ways of developing the microwave dielectric materials for different frequency ranges are discussed. It has been shown that temperature stable dielectrics with the permittivity of about 100, which are intended for the utilization in the decimetre wavelength band, can be developed by means of alio- and isovalent substitution in the cation sublattices of barium lanthanide titanates (BLTss) Ba_{6-x}Ln_{8 + 2x/3}Ti_{18}O_{54} (Ln = La-Gd). The temperature behaviour of the permittivity and dielectric loss in the BLTss has been discussed in terms of both harmonic and anharmonic contributions to the phonons of the BLT crystal lattice. It has been shown that a slight deviation from the compositional stoichiometry in both A-site and B-site deficient perovskites Ba(M_{1/3}^{2+}Nb_{2/3})O_{3} (M = Co, Zn, Mg) allows a prominent enhancement of their microwave quality factor (Q). As a consequence, new dielectrics with the extremely high quality factor (Qxf = 90000-150000 GHz), which are intended for the utilization in the centimetre wavelength band, can be developed. Some examples of the possible implementation of the developed materials are also discussed.
2
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Synthesis, Properties and Applications of some Magnetic Oxide Based Nanoparticles and Films

71%
Belous A., Tovstolytkin A., Solopan S., Shlapa Y., Fedorchuk O.
Acta Physica Polonica A
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2018
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vol. 133
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issue 4
1006-1012
EN
The work highlights peculiar features of synthesis and summarizes important properties of nanoparticles and films based on two types of oxide magnets: with spinel and perovskite-type structures. The attention is drawn to the differences in the processes underlying the formation of crystalline phase in the materials of each group. It is shown that for the spinels, the formation of weakly agglomerated crystalline nanoparticles can occur in the process of synthesis, but for the perovskite-like magnets, the formation of crystalline nanoparticles requires additional high-temperature treatment. It is demonstrated that synthesized nanoparticles and films may find wide practical applications, particularly as the heat mediators in hyperthermia treatment therapy, as components of left-handed media, ferroelectric-ferromagnetic layered structures and composite microwave resonators. They also may be used as integral parts of composite structures, which possess magnetic-field-controlled properties and display giant magnetocaloric effect.
3
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Manganite Nanoparticles as Promising Heat Mediators for Magnetic Hyperthermia: Comparison of Different Chemical Substitutions

52%
Tovstolytkin A., Shlapa Y., Solopan S., Bodnaruk A., Kulyk M., Kalita V., Zamorskyi V., Ryabchenko S., Belous A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 4
1017-1020
EN
Magnetostatic properties and AC magnetic heating characteristics of (La,Sr)MnO₃ nanoparticles with substitutions in manganese and lanthanum sublattices have been studied. The nanoparticles with average sizes in the range 25-38 nm were synthesized via sol-gel method. Fe substitution for Mn, as well as Sm substitution for La have been used in the experiment. It is shown that the increase in substitution level (for both Fe and Sm substitutions) results in lowering the Curie temperature T_{C} and weakening heating efficiency under the action of AC magnetic field. The results demonstrate that the action of AC field causes effective heating of nanoparticles at temperatures lower than T_{C}, while heating efficiency becomes strongly reduced at higher temperatures. It is proved experimentally that the substitutions in Mn sublattice result in more rapid changes of magnetic properties, as compared to the substitutions in La one. Thus, complex substitutions based on suitable combinations of substituting elements may serve as an efficient tool to "softly" tune the maximal temperature achieved during the AC magnetic field induced heating of nanoparticles, which is important for application of these materials as heat mediators for self-controlled magnetic nanohyperthermia.
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