Computational electromagnetic analysis of partially-filled rectangular waveguide at X-band frequencies

In this paper, the full-wave analysis of the direct scattering problem in the rectangular waveguide is derived. The numerical calculation results of the scattering characteristics are presented. To show the advantage of our proposed model, we compared direct problem results with three-dimensional simulation software Ansys HFSS calculations. An excellent agreement is observed when compared these two approaches

THE OVERVIEW OF BARIUM TITANATE PROPERTIES AND APPLICATION OPPORTUNITIES

Barium titanate (BT) is a ferroelectric material with a perovskite structure important in the field of electronics. Due to high flexiblity of its crystal lattice it has the capabilty to host ions with different oxidation state and careful selection of dopants could enable tailoring of barium titanate structure and electrical properties. Barium titanate doped with La, Sb, Sm, Nb and Mn will be presented in the light of structural changes and their influence on electrical properties modification. Doping with La, Sb and Sm in very low concentrations induces symmetry change from tatragonal to pseudo-cubic. La, Sb, Nb and Sm are proven to be grain growth inhibitors, with the different effect on obtained ceramics density. Dielectric permittivity value was significantly changed depending on dopant kind and concentration. Partial substitution of Ba or Ti ions by some of this dopants induced the movement of phase transition peaks to the lower temperatures and caused the formation of diffuse phase transition. In this way, the application of barium titanate can be widened from capacitors to PTCR sensors, gas and humidity sensors, etc. In the recent years, there is a growing interest for multiferroic materials with barium titanate as a main component. When being mixed with ferrites in the multiferroic composites the electrical properties of barium titanate are being compromised. Dielectric permittivity starts to decrease in comparison with pure BT ferroelectric material. Using of doped barium titanate as a part of the multiferroic material could enhance the overall dielectric permittivity of barium titanate and therefore the dielectric properties of the multiferroic material. Mixing route was used for the preparation of BaTiO3-NiFe2O4, BaTiO3-NiZnFe2O4, Ba(Sb)TiO3- NiFe2O4 composite materials. Magnetic and electrical properties of multiferroic materials have shown the dilution effect due to existence of both, ferroelectric and ferrite phases in the samematerial

Synthesis and Characterization of x BaTiOs - (1-x) NiFezO+ Composites

Multiferroic composites with the general formula x BaTiO3-(l-x) NiFezO+ (x = 0.5, 0.7, 0,8) were prepared by mixing chemically obtained powders of nickel ferrite and barium titanate. NiFezO+ powder was prepared by auto combustion method stafting from nickel and iron nitrates. After - 4 h solvent was removed and during the process of self-ignition fine powder was obtained. Thermal treatment was peformed at 1000 oC for t h and the nickel ferrite powder (NF) was formed. Barium titanate (BT) powder was prepared by a polymeric precursor method. Barium and titanium citrate solutions were peformed using barium acetate and titanium-isopropoxide. The .obtained citrates were mixed and heated at 140 oC for - 5 h. Thermal treatments was further performed at 250 ocl1 h and 300 ocl4h, and after that in the temperature range 350-800 oC for 4h barium titanate nanopowder was formed [1].Composites (BT-NF) with the general formula x BaTiO3 - (1-x) NiFe2O4 were prepared by mixing obtained powders of nickel ferrite and barium titanate in planetary ball mill for 24h. Powders were pressed and sintered at 1170 oC for 4 h. X-ray measurements confirmed the presence of NF and BT phases. The microstructure of the ceramics showed formation of polygonal grains, (Fig.1, right). Magnetic measurements of composite materials were carried (Fig.l, left). Saturation magnetization moment of composite materials decrease with barium titanate amount and the fields at which saturation occur increase with BT content. The coercivity Hc (Oe) increases with barium titanate concentration in obtained multiferroic material

CORRELATION BETWEEN STRUCTURE AND ELECTRICAL CHARACTERISTICS IN SAMARIUM DOPED BARIUM TITANATE SYSTEMS

Conventional solid-state method was used to prepare powders of barium titanate (BT) doped with different concentration of Sm. Influence of Sm addition on the structure modification, grain growth inhibition and microstructure development was studied. Dielectric properties of doped samples were significantly modified. With doping, a diffuse kind of ferro-para phase transition was induced, phase transition positions were moved and dielectric permittivity values were lowered. On the other hand, Sm doping affected the decrease of dielectric losses. The impedance complex plane plots showed a one single semicircular arc, indicating grain contribution as a main effect on the total conduction of the doped materials. On the other hand, different electro-active regions in the modulus plane plots were distinguish. The comparison between impedance and modulus scaling behavior presented the localized movement of charge carriers. P-E hysteresis loops have shown the dilution of ferroelectric properties with Sm doping

Structure and properties of BaTiO3 – Ni(1-x)Zn(x)Fe2O4 composites

NiZnFe2O4 powder was prepared by auto-combustion method starting from nickel, zinc and iron nitrates. Barium titanate powder was prepared with same method using titanyl nitrate and barium nitrate. Multiferroic composites with formula BaTiO3– Ni(1-x)ZnFe2O4 (x = 0.3, 0.5, 0.7) were prepared from obtained powders of NZF and BT by mixing in planetary mill for 24h. Powders were pressed and sintered at 1170 oC for 4 h. Samples were characterized by XRD, Raman, SEM, IR, magnetic and electrical measurements. X-ray and Raman measurements confirmed the presence of NZF and BT phases. The microstructure indicated formation of polygonal and rounded grains

ELECTRICAL PROPERTIES OF BARIUM TITANATE CO- DOPED WITH Nb AND Mn

A modified Pechini process was used to prepare nanopowders of barium titanate (BT) co-doped with niobium and manganese. Prepared BT compositions were (1) BT doped with 0.4 mol% Nb and 0.1 mol% Mn (BT1); (2) 0.4 mol% Nb and 0.05 mol% Mn (BT2) and (3) 0.8 mol% Nb and 0.01 mol% Mn (BT3). The XRD results of sintered samples showed the formation of barium titanate tetragonal crystal structure. Microstructure was consisted of polygonal grains but the differences in the grain size, homogeneity and porosity between the doped ceramics were noticed. The addition of dopants influenced the grain size and microstructure development. The dielectric measurements of all ceramics showed the behavior of classical ferroelectric material. In comparison with pure barium titanate, structural transition of all co-doped ceramics are shifted to lower temperatures. The real permittivity value increase in all co-doped ceramics in the whole frequency range, reaching much higher values then in pure barium titanate ceramics obtained by polymeric precursors method. The analysis of impedance spectrum at higher temperatures showed the presence of both, grain interior and grain boundary effects

Dielectric properties of Bi-substituted LDHs synthesized by co-precipitation and sol-gel methods

Magnesium-aluminum-bismuth layered double hydroxides (Mg3Al1-xBix; LDHs) were prepared using both coprecipitation and sol-gel methods. For the preparation of Mg/Al/Bi LDH by the co-precipitation method, the appropriate amounts of dissolved starting materials (Al(NO3)3 · 9H2O, Mg(NO3)2 · 6H2O and Bi(NO3)3 · 5H2O) were mixed with a solution of NaHCO3:NaOH. In the sol-gel processing, the precursor Mg-Al-Bi-O gels were synthesized using the same starting materials and ethylene glycol as complexing agent. The mixed-metal oxides obtained by subsequent heating of Mg-Al-Bi-O gels at 650 °C were reconstructed to Mg3Al1-xBix LDHs in water at 80 °C. All the synthesized products were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and dielectric measurements.publishe

Temperature-Induced Structural Transformations in Undoped and Eu3+-Doped Ruddlesden–Popper Phases Sr2SnO4 and Sr3Sn2O7: Relation to the Impedance and Luminescence Behaviors

We report that luminescence of Eu3+ ion incorporated into Ruddlesden–Popper phases allows monitoring phase transition in powders (instead of single crystals), in a time-efficient manner (compared to neutron diffraction), and importantly, with greater sensitivity than previous methods. Crystal structure and dielectric response of undoped and 0.5%Eu3+-doped Sr3Sn2O7 ceramics were studied as a function of temperature over the temperature range of 300–800 K. The luminescence studies of 0.5%Eu3+-doped Sr2SnO4 and Sr3Sn2O7 samples were performed in the temperature range of 80–500 K. These results were compared with the respective dependences for the undoped compounds. The structural transformations in 0.5%Eu3+-doped Sr3Sn2O7 were found at 390 and 740 K. The former is associated with the isostructural atomic rearrangement that resulted in a negative thermal expansion along two of three orthorhombic crystallographic axes, while the latter corresponds to the structural transition from the orthorhombic Amam phase to the tetragonal I4/mmm one. A similar temperature behavior with the structural transformations in the same temperature ranges was observed in undoped Sr3Sn2O7, although the values of lattice parameters of the Eu3+-doped and undoped compounds were found to be slightly different indicating an incorporation of europium in the crystal lattice. A dielectric anomaly associated with a structural phase transition was observed in Sr3Sn2O7 at 390 K. Optical measurements performed over a wide temperature range demonstrated a clear correlation between structural transformations in Eu3+-doped Sr2SnO4 and Sr3Sn2O7 and the temperature anomalies of their luminescence spectra, suggesting the efficacy of this method for the determination of subtle phase transformations

Magneto-dielectric characterization of TiO2-CoFe2O4 derived ceramic composites

Dielectric permittivity (ε′), magnetic permeability (µ′) and dielectric and magnetic loss (tan δε and tan δµ, respectively) of magneto-dielectric cobalt ferrite-titania (CFO-TO) ceramic composites are determined from 200 to 300 MHz. The four different combinations of phases - that can be produced in the sintered composite, according to the starting CFO/TO molar ratio - allow to tune the macroscopic permittivity and permeability. For the first time impedance, miniaturization and magneto-dielectric loss of the four classes of composites are calculated and discussed. The displayed miniaturization factors between 4.4 and 8.2 in the very-high frequency (VHF) range corroborate their potential application as magneto-dielectric substrate materials for antennas. Remarkably, the ceramic composites characterized by 2 vol.% and 3 vol.% of CFO and TO, respectively, dispersed in Fe2CoTi3O10 (FCTO) matrix display a magneto-dielectric loss lower than 0.07 and a miniaturization factor of 4.8

Influence of Processing Method on Dielectric Properties of BaBi4Ti4O15 Ceramics

Bismuth layer-structured ferroelectrics (BLSF), first described by Aurivillius, have attracted much attention for their application in non-volatile random access memory and high temperature piezoelectric devices. BaBi4Ti4O15 (BBT) is a well-known member of BLSFs. Considering the grain size affect reduction of conductivity of most of BLSF compounds [1] this paper dealing with effect of mechanochemical assisted synthesis method on electrical, dielectric and conductive propefties of BBTcompounds. BBT was prepared by solid state reaction from mixture of oxides: BaO, Ti02 and BizO: which was previously milled for 6 h (BBT-MA). The mixture was heated at 850 oCfor 4 h. As a comparison, the same ceramics were prepared throught conventional solid state reaction (BBT-SS). The same oxides mixture was homogenized for 24 h in isopropanol and calcinated at 950 oC for 4 h which is 100 oC higher temperature than for MA procedure. Sintering process was carried out at 1130 oC for t h in both synthesis methods. Smaller plate like grains are noticed in BBT ceramics prepared from powders obtained by MA process comparing to SS process (Fig 1.). In the temperature dependence of the dielectric permittivity, the maximum associated to the Curie temperature was higher and narrower in ceramics prepared by SS method. Influence of the grain and grain boundaries contribution to the dielectric behaviour in both ceramics were analyzed through impedance spectroscopy