Pavel Astafev

The paper studies the nonlinear electrical response of dispersed-crystalline lead zirconate titanate powders (PbZr[ ]Ti[ ]O ₃ , PZT) in the microwave range (8.2–12.4[ ]GHz). The main attention is paid to the influence of temperature and incident wave power on the dielectric properties of the material, especially near the morphotropic phase boundary (MPB) and phase transitions (PTs). The experiments were carried out using a waveguide measuring cell and a vector network analyzer. The results showed that the permittivity and losses of the material depend on the frequency, temperature and microwave power. A broad relaxation maximum of losses was found at ∼12[ ]GHz, which shifts to the low-frequency region upon heating. It is assumed that this maximum is due to the presence of several competing polarization mechanisms associated with the reorientation of dipoles in the B sublattice. At higher powers (>5[ ]dBm), nonlinear effects were observed, including the disappearance of the relaxation maximum, which may be due to local heating and destabilization of dipole configurations. The obtained data emphasize the importance of taking into account cooperative interactions and structural transitions when analyzing the dielectric response of PZT in the microwave range.

The paper presents the results of a study of the microwave absorption properties of ceramic materials based on bismuth ferrite containing rare earth elements, as well as systems of solid solutions ([ ])BiFeO₃–xPbFe[ ]Nb[ ]O₃ in a wide range of component concentrations. The methodology for measuring and calculating the parameters of samples of the materials under study is described. The influence of structural and microstructural factors on the average and maximum level of microwave absorption of the materials under study in a wide frequency range is analyzed. A comparison of the microwave absorbing properties of these materials with industrial absorbers has been carried out, and prospects for application in microwave technology have been shown.

Ceramic samples of Bi_1−xHo_xFeO₃, where x = 0.00–0.50, with a modifier concentration variation step ∆x = 0.05–0.10, were prepared by a two-step solid-phase synthesis followed by sintering using conventional ceramic technology. X-ray phase analysis showed that all the solid solutions studied were formed in the presence of impurities. With increasing Ho concentration, a non-monotonic shift in all loss maxima towards the low-frequency region is observed, as well as an increase in their half-width. An increase in the external temperature leads to a monotonic shift in the absorption maxima towards the low-frequency region, which enables the necessary control of the microwave parameters in the X band. A conclusion has been drawn on the feasibility of using the data obtained in the design of new functional materials based on BiFeO₃, as well as devices with thermally controlled frequency.

The electrodynamic properties of lead zirconate titanate ceramic solid solutions, exhibiting ferro-antiferroelectric phase transition, are investigated at microwave frequencies in a wide temperature range. Significant changes in the electrodynamic response are found, presumably associated with structural rearrangements accompanying the sequence of phase transitions between para-, ferro-, and antiferroelectric states. The phenomena observed in the experiments are considered under conditions of changing temperature and concentrations of the components; several independent measurement techniques were used for their unambiguous identification.

In this paper, a brief review of the current state of research on ferroelectric, ferromagnetic, and multiferroic materials in the microwave range is given, and the main research methods are described. The main areas of application of functional materials in radio electronics are outlined. Multicomponent ferroelectric media based on ferroelectric (PbTiO₃), antiferroelectric (PbZrO₃), and relaxors (PbMg_1/3Nb_2/3O₃) are considered promising radio-absorbing materials. A method for comparing the electrical parameters of samples using a microstrip line and a network analyzer is described in detail, in which cylindrical samples were placed on a microstrip line. The measurements were carried out in the frequency range 10 MHz–20 GHz. Based on the frequency dependences of the S parameters, the relationships between the resonant frequencies of the samples and their composition were determined. The frequency dependences of the absorption coefficient were calculated for materials of various compositions. For each composition, the effective absorption band was calculated, and a pattern of its distribution over the concentrations of the system components was plotted. For empty areas of the phase diagram, interpolation was performed using the obtained results, which made it possible to obtain a qualitative idea of the radio-absorbing properties of the entire system. It was revealed that the compositions with the greatest variety of different phases had the widest absorption band. The results obtained will help in future research and composition selection for further development of microwave devices such as dielectric resonators, filters, and attenuators.