Nickel ferrite solid solutions remain one of the main materials for a whole range of applications, including microwave equipment and components, the requirements for parameters and homogeneity of ...materials are constantly increasing. In this work, Ni
1-x
Zn
x
Fe
2
O
4
nanoparticles with an average diameter of 12.5 nm were successfully synthesized by the microwave-assisted urea method. The temperature of a single-phase product formation was 400 °C, which is lower compared to more common precipitation from aqueous solution methods or solid-state route. Ni
1-x
Zn
x
Fe
2
O
4
materials demonstrate high saturation magnetization and low coercive force. The magnetization changes with increasing Zn concentration and reaches the maximum at x = 0.5. Also, the increase in zinc content leads to an increase in the lattice parameters. The average size of ferrite nanoparticles synthesized by the microwave-assisted urea method is smaller compared to ferrites synthesized earlier by the co-precipitation method. Also, lower treatment temperatures provide higher stoichiometry, and homogeneity of materials while magnetization difference is negligible. These research results provide a general and effective route to synthesize other nanostructures for a variety of microwave components.
•La0.5Li0.5TiO3 with improved dielectric properties were produced using Na.•High permittivity (ε~4·104 at 1 Hz) was achieved.•The number of vacant sites is controlled by the amount of Na.•The grain ...bulk and boundary contribute to the electrical properties.
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Ceramic samples of Na-doped lithium lanthanum titanates have been synthesized by solid-state reaction technique. Scanning electron microscopy has shown that the grain size of ceramics in La0.5Li0.5−xNaxTiO3 solid solutions decreases with an increase in sodium concentration. Complex impedance spectroscopy measurements demonstrate that the origin of the electrical properties in La0.5Li0.5−xNaxTiO3 can be attributed to equivalent circuit consist of 3 elements, when x=0–0.4 and 2 elements when x=0.5. The dielectric constant and dielectric loss of polycrystalline samples of La0.5Li0.5−xNaxTiO3 have been investigated over a large frequency range. It has been found that the largest permittivity value is can be observed in La0.5Li0.4Na0.1TiO3 ceramic.
Ceramics with nominal chemical composition CaCu3Ti4O12 (CCTO), CaCu3Ti3.96Al0.04O11.96F0.04 (CCTOAF), and Ca0.98Mg0.08Cu2.94Ti3.96Al0.04O11.96F0.04 (CCTOMAF) were prepared by the solid-state ...reactions technique. Using SEM, EDX, XPS, EPR, NMR, and complex impedance spectroscopy, the microstructure, elements distribution, chemical composition of grains and grain boundaries, and the dielectric response of ceramics were investigated. In the ССТО, CCTOAF, and CCTOMAF series, the average grain size increases, the degree of copper segregation at the grain boundaries is inversely related to grain size, and the dielectric loss decreases from 0.071 to 0.047 and 0.030, respectively, while dielectric permittivity ε′ at 1 kHz is 5.6 × 104, 7.1 × 104, and 4.3 × 104, respectively. Additives of Al, Mg, F and milled particles (ZrO2, Al2O3, and SiO2) can either partially introduce into the perovskite structure or form low-melting eutectics at the grain boundaries, causing abnormal grain growth. The presence of copper ions in various oxidation states, as well as evidence of exchange spin interactions between them, was confirmed in all samples.
Barium cuprate has been synthesized using secondary induction heating. It is found that the single-phase product is formed when the equimolar mixture of Ba(NO
3
)
2
and CuO is kept in the induction ...furnace for 40 min at 1173 K. Reflections in the diffraction patterns are indexed in cubic syngony (space group Im3m). Parameters of the unit cell are refined applying the Rietveld method: a = = 1.82996(7) nm and V = 6.1281(7) nm
3
(
R
Bragg
= 4.42% and
R
f
= 3.61%). Iodometric titration data show that a half of the copper atoms are in oxidized state in BaCuO
2.25
. Partial oxidation of copper (Cu
2.5+
) influences the electrical properties of the synthesized cuprate, examined using impedance spectroscopy within the range 453 K ≤T ≤ 593 K. The electrical conductivity of BaCuO
2.25
, which is nonstoichiometric toward oxygen, exhibits semiconducting nature with activation energy
E
dc
= 0.29 eV.
Ceramic CaCu3Ti4O12 (ССТО), Ca0.98Cu3Ti4O11.96F0.04 (CΔCTOF), and CaCu3Ti4O11.92F0.08 (CCTOF) were synthesized by the solid-state reaction technique. Fluorine stimulates the formation of Cu-depleted ...grains, Cu3+ ions, and Cu-rich composites CuO-xCCTO-yTiO2-zSiO2-wСaF2 (w < z < y < x < 1), which include parts of grinding bodies. The observed structures are distinct from simple grain boundaries of the perovskite phase. They exhibit a terrace-ledge-kink (TLK) morphology and, in some cases, the presence of twinning planes, both independent of fluorine content. They are responsible for the nanoscale barrier layer capacitance (NBLC) component of the dielectric response of both CCTO and CuO ceramics. Changes in the unit cell parameter a, and titanium and copper valences indicate that Ca2+ ions occupy part of Cu vacancies in the grains of CCTO and CCTOF. In CΔCTOF, Ti3+ ions in the copper sublattice were found for the first time using NMR. The maximum ε′1kHz = 6.9 × 104 demonstrates CΔCTOF and the minimum tan δ = 0.045 is characteristic of CCTOF.
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Ceramics with nominal chemical composition CaCu
Ti
O
(CCTO), CaCu
Ti
Al
O
F
(CCTOAF), and Ca
Mg
Cu
Ti
Al
O
F
(CCTOMAF) were prepared by the solid-state reactions technique. Using SEM, EDX, XPS, EPR, ...NMR, and complex impedance spectroscopy, the microstructure, elements distribution, chemical composition of grains and grain boundaries, and the dielectric response of ceramics were investigated. In the ССТО, CCTOAF, and CCTOMAF series, the average grain size increases, the degree of copper segregation at the grain boundaries is inversely related to grain size, and the dielectric loss decreases from 0.071 to 0.047 and 0.030, respectively, while dielectric permittivity ε' at 1 kHz is 5.6 × 10
, 7.1 × 10
, and 4.3 × 10
, respectively. Additives of Al, Mg, F and milled particles (ZrO
, Al
O
, and SiO
) can either partially introduce into the perovskite structure or form low-melting eutectics at the grain boundaries, causing abnormal grain growth. The presence of copper ions in various oxidation states, as well as evidence of exchange spin interactions between them, was confirmed in all samples.
The synthetic availability of mol-ecular water oxidation catalysts containing high-valent ions of 3d metals in the active site is a prerequisite to enabling photo- and electrochemical water splitting ...on a large scale. Herein, the synthesis and crystal structure of di-ammonium {μ-1,3,4,7,8,10,12,13,16,17,19,22-dodeca-aza-tetra-cyclo-8.8.4.13,17.18,12tetra-cosane-5,6,14,15,20,21-hexa-onato}ferrate(IV) acetic acid tris-olvate, (NH4)2FeIV(C12H12N12O6)·3CH3COOH or (NH4)2FeIV(L-6H)·3CH3COOH is reported. The FeIV ion is encapsulated by the macropolycyclic ligand, which can be described as a dodeca-aza-quadricyclic cage with two capping tri-aza-cyclo-hexane fragments making three five- and six six-membered alternating chelate rings with the central FeIV ion. The local coord-ination environment of FeIV is formed by six deprotonated hydrazide nitro-gen atoms, which stabilize the unusual oxidation state. The FeIV ion lies on a twofold rotation axis (multiplicity 4, Wyckoff letter e) of the space group C2/c. Its coordination geometry is inter-mediate between a trigonal prism (distortion angle φ = 0°) and an anti-prism (φ = 60°) with φ = 31.1°. The Fe-N bond lengths lie in the range 1.9376 (13)-1.9617 (13) Å, as expected for tetra-valent iron. Structure analysis revealed that three acetic acid mol-ecules additionally co-crystallize per one iron(IV) complex, and one of them is positionally disordered over four positions. In the crystal structure, the ammonium cations, complex dianions and acetic acid mol-ecules are inter-connected by an intricate system of hydrogen bonds, mainly via the oxamide oxygen atoms acting as acceptors.
The amplitude and phase characteristics of metamaterial cells consisting of microstrip and dielectric resonators (DRs) were studied. Circuits containing resonators of fundamentally different quality ...factors in the microwave range and excited on different types of oscillations have two independent energy ways, which allows the simulation of Fano resonances and electromagnetically induced transparency (EIT). The effects associated with the anomalous dispersion of the metamaterial cell as well as the associated positive values of the group delay (GD) are demonstrated. The experimental and calculated characteristics of metamaterial cells were compared. As the model of metamaterial cell calculation, the lattice circuit of an all-passing filter based on lumped elements was used. It was shown that the numerical calculations of systems exhibiting resonant phenomena (including the Fano effect) can be simplified based on the four-pole network containing the following parameters: unloaded, external, and loaded quality factors of resonators and detuning between their resonant frequencies. The calculated and measured characteristics were found to be in good agreement, which indicates the adequacy of the proposed models.
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