Journal of Advanced Dielectrics

A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene) copolymer P(VDF-TrFE) and ferroelectric ceramics of barium lead zirconate titanate (BPZT) solid solution is presented in this work. The composite films containing up to 50 vol.% of BPZT grains with size $\sim$1$\mu$m were prepared by the solvent cast method. Frequency dependences of real and imaginary components of the complex permittivity were determined. The concentration dependence of the dielectric constant was discussed.

Frequency selective surface (FSS) has been extensively studied due to its potential applications in radomes, antenna reflectors, high-impedance surfaces and absorbers. Recently, a new principle of designing FSS has been proposed and mainly studied in two levels. In the level of materials, dielectric materials instead of metallic patterns are capable of achieving more functional performance in FSS design. Moreover, FSSs made of dielectric materials can be used in different extreme environments, depending on their electrical, thermal or mechanical properties. In the level of design principle, the theory of metamaterial can be used to design FSS in a convenient and concise way. In this review paper, we provide a brief summary about the recent progress in all-dielectric metamaterial frequency selective surface (ADM-FSS). The basic principle of designing ADM-FSS is summarized. As significant tools, Mie theory and dielectric resonator (DR) theory are given which illustrate clearly how they are used in the FSS design. Then, several design cases including dielectric particle-based ADM-FSS and dielectric network-based ADM-FSS are introduced and reviewed. After a discussion of these two types of ADM-FSSs, we reviewed the existing fabrication techniques that are used in building the experiment samples. Finally, issues and challenges regarding the rapid fabrication techniques and further development aspects are discussed.

The influence of the $B$-site ion substitutions in ($1-x)$(Bi${}_{1∕2}$Na${}_{1∕2})$TiO₃–$x$BaTiO₃ system of solid solutions on the relative stability of the antiferroelectric (AFE) and ferroelectric (FE) phases has been studied. The ions of zirconium, tin, and (In${}_{0.5}$Nb${}_{0.5})$, (Fe${}_{0.5}$Nb${}_{0.5})$, (Al${}_{0.5}$V${}_{0.5})$ ion complexes have been used as substituting elements. An increase in the concentration of the substituting ion results in a near linear variation in the size of the crystal lattice cell. Along with the cell size variation, a change in the relative stability of the AFE and FE phases takes place according to the changes of the tolerance factor of the solid solution. An increase in the tolerance factor leads to the increase in the temperature of the FE–AFE phase transition, and vice versa. Obtained results indicate the way for raising the temperature of the FE–AFE phase transition in (Bi${}_{1∕2}$Na${}_{1∕2})$TiO₃-based solid solutions.

Quaternary glasses were successfully fabricated using melt quenching technique based on the chemical compound composition ($x$)Bi₂O₃–($0.5-x$) ZnO–(0.2)B₂O₃–(0.3)SiO₂, where ($x=0.1$, 0.2, 0.3, 0.4, 0.45) mole. The sources of SiO₂ was produced from rice husk ash (RHA) at 99.36% of SiO₂. The Urbach energy was increased from 0.16eV to the 0.29eV as the mole of Bi₂O₃ increased in the glass structure. The indirect energy band gap is indicated in decrement pattern with 3.15eV towards 2.51eV. The results of Urbach energy and band gap energy that were obtained are due to the increment of Bi${}^{3+}$ ion in the glass network. The refractive indexes for the prepared glasses were evaluated at 2.36 to 2.54 based on the Lorentz–Lorentz formulation which correlated to the energy band gap. The calculated of molar polarizability, electronic polarizability and optical basicity exemplify fine complement to the Bi₂O₃ addition in the glass network. The glass sample was indicated in amorphous state.

The temperature dependence of the specific heat of the single crystal Pb(In${}_{0.5}$Nb${}_{0.5}$)O₃-Pb(Mg${}_{1∕3}$Nb${}_{2∕3}$)O₃-PbTiO₃ (PIN-PMN-PT) was obtained at 80–500K by means of ac-calorimetry, and comparison with the calorimetric data for PMN was made, allowing one to determine absolute values of the specific heat of PIN-PMN-PT. For the high-temperature region ($T>200$K), the background heat capacity was calculated, the anomalies of the heat capacity for both compounds were determined, and the hump of the temperature dependence of specific heat PIN-PMN-PT was detected for the first time.

It is important to determine the dielectric characteristics of semiconductor encapsulation materials based on epoxy resins. We employed the dielectric spectroscopy technique to investigate the dielectric relaxation in the presence of water and how it changes the relaxation. It was observed that the dielectric relaxation of the material was significantly influenced by absorbed water, the local segmental motion (also known as Johari–Goldstein ($\beta$) relaxation) was influenced most by the presence of the water, it was modified by the wet sample compared to dry one, and required high activation energy. The relaxation related to the glass transition was contributed by the cooperative motion (the $\alpha$-relaxation) of the epoxy resin system. The $\alpha$-relaxation was shifted to a low temperature in the wet sample compared to dry one. The relaxation was modeled with a clear Vogel–Fulcher–Tammann–Hesse (VFTH) behavior; the Vogel temperature of the wet sample was 8K lower than the dry sample. The presence of water acts as a plasticizer for the molecular relaxation, and speed-up the cooperative process. The measured data were also used to estimate the electrical properties of the resin system by employing an effective-medium model together with a porous media continuum model by taking into account the physical properties of the system. It is already known that the influence of water in semiconductor packaging is important in sensitive applications. The presented measurements and the analysis method would be appreciated within the semiconductor packaging community to improve material selection and performance evaluation efforts.

This work focuses on the structural, electrical and magnetic properties of Bi${}_{0.8}$Tb${}_{0.1}$Ba${}_{0.1}$Fe${}_{0.9}$Ti${}_{0.1}$O₃ ceramics, fabricated by solid state reaction procedure. XRD forms of the samples at RT exhibited perovskite phase through the hexagonal structure at room temperature. Dielectric studies of the materials with frequency at different temperatures (25–400${}^{\circ }$C) exhibit two dielectric anomalies, first at 175${}^{\circ }$C (ferroelectric–ferroelectric transition) and second at around 320${}^{\circ }$C (ferroelectric–paraelectric transition). The Curie temperature moved towards the low side temperature with the increase in frequency. The less value of activation energy got for these samples could be attributed to the influence of electronic contribution to the conductivity. A significant change in the magnetic studies was observed for Bi${}_{0.8}$Tb${}_{0.1}$Ba${}_{0.1}$Fe${}_{0.9}$Ti${}_{0.1}$O₃ ceramic. The impedance analysis confirms the non-Debye type nature of the ceramic and relaxation frequency moved to a higher temperature. The Nyquist plot and conductivity studies showed the NTCR behavior of samples. The highest magnetization field was found at temperature $-$268.15${}^{\circ }$C.

The paper presents the structural and ferroelectric results for Sr${}_{1-x}$Ba_xBi₂Nb₂O₉($x=0.30$; 0.85) thin films, which were obtained by using dip-coating. The solutions containing the desirable ions were prepared from the powders of the previous studied ceramic samples. The films were deposited at room temperature on Fluorine-doped Tin Oxide (FTO) substrates and submitted to a heat treatment for crystallization. The films were characterized by using scanning microscopy electronic, energy dispersive spectroscopy and ellipsometry. Hysteresis ferroelectric loops were obtained, at room temperature, by using a Sawyer-Tower circuit at several frequencies. A well-defined grain structure was observed for both compositions. The energy dispersive spectroscopy (EDS) measurements revealed the presence of the corresponding elements from the chemical composition of the ceramic systems. The band-gap energy was around 3.3eV for both samples. Typical hysteresis loops for normal and relaxor ferroelectrics were obtained for $x=0.30$ and 0.85, respectively.