Structural transformations of CsPbBr₃ were studied by multiple techniques (dielectric, Raman, EPR spectroscopy and XRD) in an extended temperature range.

The recent discovery of the large piezoelectric response of Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT) ceramics induced by samarium doping has provided a substantially improved functionality to the group of lead-based relaxor-ferroelectric materials. Different mechanisms have been so far proposed for the large piezoelectricity; however, the explanations are contradictory and focused on a unified description. Here, we use nonlinear harmonic piezoelectric measurements combined with multiscale structural analysis to clarify the origins of the ultrahigh piezoelectric response of samarium-doped PMN-PT. Our methodological approach allowed us to separate the multiple piezoelectric contributions, revealing their quantitative role in the total response. The results show that the ultrahigh piezoelectricity cannot be attributed to a single mechanism but is rather a complex combination of different contributions originating from the multiple effects of samarium doping on the long- and short-range structure of PMN-PT. The study offers a baseline for future engineering of the key material parameters affecting the large piezoelectric response of relaxor-ferroelectric ceramics.

We report on the design of highly absorptive thermostable composite materials for microwave applications. Ceramics comprising the thermostable phosphate host and silicon carbide particles or whiskers were studied in a wide frequency range from several Hertz up to microwaves. It was demonstrated that a thin layer of ceramics placed on the back-reflector absorbs perfectly at the 30 GHz frequency. In the case of a free-standing ceramic composite layer being 1 mm thick, it provides more than 50% of absorption.

In ferroelectrics, the effects of acceptor doping on electrical and electromechanical properties, often referred to as the “hardening” effects, are commonly related to domain-wall pinning mechanisms mediated by acceptor-oxygen-vacancy defect complexes. In contrast, the hardening effects in relaxor ferroelectric materials are complicated by the nano-polar nature of these materials, the associated dynamics of the polar nano-regions and their contribution to polarization, and the characteristic freezing transition between the ergodic and the non-ergodic phases. To shed light on this issue, in this study, we investigate the role of the acceptor (Mn) doping on the temperature-dependent broadband dielectric permittivity, high-field polarization–electric-field (P–E) hysteresis and electrocaloric (EC) response of 0.9Pb(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃ (PMN-10PT) relaxor ferroelectric ceramics. The results suggest strong pinning effects, mediated by the acceptor–oxygen-vacancy defect complexes, which manifest similarly both in the ergodic and in the non-ergodic phases of PMN-10PT as revealed by the doping-induced suppression of the frequency dispersion of the permittivity maximum and pinched high-field hysteresis loops. In addition to these pinning effects, the Mn doping reduces the freezing temperature (T_f) by ∼50 °C with respect to the undoped PMN-10PT. This is reflected in the EC response, which becomes less temperature dependent, making defect engineering a valuable approach for designing EC materials with an extended operational temperature range.

The full-wave analysis was applied for a coaxial line (i.e., transmission line) that has a “short-circuited” discontinuity. The discontinuity has a radius less than or equal to the inner radius of the coaxial line. The “sample region” can be considered as a partially filled circular waveguide. Such a structure is very practical and is of particular interest for the dielectric spectroscopy applications. It takes into account the inhomogeneous field distribution, which is the limiting factor for the determination of high dielectric permittivity values at microwave frequencies. The direct problem was solved by using the mode-matching technique, and the relationship between the complex reflection coefficient and the dielectric permittivity of the cylindrical sample was obtained. By solving the inverse problem, it is possible to obtain the complex dielectric permittivity from the experimental values of the scattering matrix. The results were verified by the finite element modeling of the system and applied for particular materials. The correspondence between these approaches is excellent. This method is very suitable for the determination of permittivity, which exceeds several thousands (it is applicable for any type of material). It extends the frequency range where the permittivity can be determined reliably. There is no necessity to prepare samples with different geometries (i.e., surface area and thickness).