D.D. Tatarchuk

Microwave dielectric resonator frequency control

Constituent dielectric resonators and dielectric-metal mirror resonant structures capable of electrically controlling frequency with a preservation of high Q-factor were studied. Resonant frequency control could be realized by means of one structural component small mechanical shift using electrostrictive actuator. Examined dielectric resonant devices allow to change their resonant frequency up to 10-30%.

Thermal stability of oscillatory systems based on split dielectric resonator

The method of calculation and experimental studies of the temperature-stable oscillating system based on the use of the composite dielectric resonator (DR) with transverse dielectric inclusions are discussed. The method of calculation and results of simulation of such structures were reviewed. One possible solution to improve the thermal stability of oscillatory systems based on DR is to use a split dielectric resonator (SDR) with transverse dielectric inclusions as compensating element. Using the SDR with a cross-dielectric adjustable air gap provides a shift of resonant frequencies over a wide range while maintaining the high quality factor of the oscillating system. The advantage of such constructions is the absence of the complex temperature-compensated systems, simplicity and technological effectiveness in production.

UHF methods of measuring the parameters of the microwave dielectric materials based on composite dielectric resonator

The article analyzes the microwave methods for measuring the material parameters, showing their advantages and disadvantages, discussed the criteria for selecting the measurement method. The authors proposed a modification of the method of the composite dielectric resonator. The proposed method has a high sensitivity in the measurement of dielectric constant and loss. References 4, figures 6, tables 1.

High hydrostatic pressure effect on functional properties of nanopowder La 0.6 Sr 0.3 Mn 1.1 O 3-δ compacts with various dispersion

Nanopowder La<inf>0.6</inf>Sr<inf>0.3</inf>Mn<inf>1.1</inf>O<inf>3−δ</inf> compacts by the oxide-salt, co-precipitation and atomization hydrolysis technologies have been obtained. Structure and its defects, average particle size and functional properties of the nanopowder compacts by X-ray diffraction, thermogravimetric, resistance, magnetic, ⁵⁵Mn NMR, magnetoresistance and BET methods have been investigated. Connections between the dispersion of nanopowders and their structural, magnetic, resistance, magnetoresistance and baroresistance properties have been established. Broad and asymmetric ⁵⁵Mn NMR spectra testify the high-frequency electron double exchange Mn³⁺↔O²⁻↔Mn⁴⁺ and indicate inhomogeneous environment of Mn by other ions and vacancies. The increase in high hydrostatic pressure up to 1.6 GPa leads to decrease in resistivity and activation energy as well as raise in density, coercive force, magnetoresistance and baroresistance effects of the nanopowder compacts.

Paraelectricity and paramagnetism in thermostable microwave dielectrics

High dielectric constant microwave dielectrics are basic materials for dielectric resonators, filters, microwave substrates, etc. These dielectrics can be improved through understanding of their polarization physical nature. High value of permittivity with small dielectric losses in frequency range of 1…100 GHz can be realized only due to quick-response mechanisms of polarization. In the report, firstly, main motive of increased polarizability in paraelectrics is explained. Secondly, it is determined that composition of microwave dielectrics should be based on “hard” paraelectrics, which structure resists to polar phases formation. Thirdly, we proved that addition of rare-earth paramagnetic ions supports high thermal stability.

Influence of the K+ ions and the superstoichiometric manganese on structure defects, magneto-transport and dielectric properties of magnetoresistive La0.7Ca0.3-xKxMn1+xO3-δ ceramic

The structure, its defects, nanostructural clustering and functional properties of the La0.7Ca0.3-xKxMn1+xO3-δ ceramic with x = 0–0.3 have been investigated by x-ray diffraction, thermogravimetric, SEM, resistance, magnetic, magnetoresistance and dielectric spectroscopy methods. We establish that the lattice parameter of the cubic structure increases when the Ca2+ ions are substituted with ions of K+. We show that the real perovskite structure contains different valence states of manganese MnA2+,MnB3+ and MnB4+ in A- and B-positions, as well as vacancy type point defects, in the form of anionic V(a) and cationic V(c) vacancies. The increase in the content of the superstoichiometric manganese is connected to the nanostructured clustering process. We find that K+ and superstoichiometric manganese cause the increase in relative permittivity e′ and dielectric loss tangent angle tg δ. The experimental phase diagram of the magnetic state has been constructed and allows determining the composition of the magneto...

Magnetotransport and dielectric properties of Bi-containing La 0.6 Sr 0.15 Bi 0.15 Mn 1.1-x B x O 3-δ rare-earth manganites with B = Cr, Fe, Co, Ni

The effect of the replacement of manganese by Spions of transition metals on the structural, microstructural, dielectric, and magnetotransport properties of nonstoichiometric La<inf>0.6</inf>Sr<inf>0.15</inf>Bi<inf>0.15</inf>Mn<inf>1.1-x</inf>B<inf>x</inf>O<inf>3-δ</inf> compositions with B = Cr, Fe, Co and Ni (0 ≤ χ ≤ 0.3) was investigated. It is shown that in all compositions a weak change for the lattice parameter of the rhombohedral perovskite structure is observed. It is established that the real structure is defective and contains cationic V^(c) and anionic V^(a) vacancies. With increasing χ, an increase in the resistivity and the absence of a metal-semiconductor phase transition for χ > 0.20 are observed. The electron-phonon interaction constant /ph was determined. The most significant change in the structural and functional properties was observed for the compositions with B = Fe, for which constant γ<inf>ph</inf> ≈ 7.7 achieves a maximum value. At χ = 0.05, an increase in magnetoresistance effect of the tunnel type is observed.

Measuring of the microwave materials parameters on the base of the inhomogeneous microstrip resonator method

In this paper the method for measuring the dielectric constant and dielectric loss tangent of the dielec-tric material in the microwave range of wavelengths using the inhomogeneous microstrip resonator is pre-sented. The measurement technique and the design of the measuring cell are described, the theoretical basis of the method and results of experimental studies are given. Reference 9, figures 2, tables 1.In this paper the method for measuring the dielectric constant and dielectric loss tangent of the dielec-tric material in the microwave range of wavelengths using the inhomogeneous microstrip resonator is pre-sented. The measurement technique and the design of the measuring cell are described, the theoretical basis of the method and results of experimental studies are given. Reference 9, figures 2, tables 1.

Structure imperfection and dielectric properties of single-phase multifferoic Bi1-xLaxFeO3-δ

Using the rapid liquid sintering method the samples of multiferroic Bi_1-xLa_xFeO_3-δ (x = 0, 0.1, 0.3 and 0.5) were obtained. Their structure and dielectric properties were investigated. The X-ray diffraction, thermogravimetric, scanning electron microscopy and dielectric spectroscopy methods were used. The molar formulas of defective structure Bi_1-xLa_xFeO_3-δ were defined. An analysis of the frequency dependence of the relative permittivity ε(f) and dielectric loss tangent tanδ (f) at the low frequency (f = 1...10⁶ Hz) and microwave (f = 8...12 GHz) bands was conducted. It was established that the Bi_0.9La_0.1FeO₃ composition has the greatest value of dielectric permittivity.

Microwave dielectrics with unstable electronic spectrum

High dielectric constant microwave dielectrics are basic materials for dielectric resonators and filters, as well as for microwave substrates, dielectric waveguides, etc. These dielectrics are possible to improve only through the understanding of physical nature of their polarization. High value E without significant absorption electrical energy at the frequency range of 10…100 GHz can be realized only at the expense of quick-response mechanisms of polarization. The theoretical possibility to obtain thermal stable dielectrics with high εmw but at very low temperatures exists. One previously unknown possibility to combine high permittivity, low loss factor with thermal stability is discussed. It is based on fast-response electronic-phonon mechanism of polarization in dielectrics with the unstable electronic spectrum (like in the quasi one-dimensional crystals of TTF-TCNQ type).