Journal of Electroceramics最新文献

Lithium and iron co-doped cadmium oxide Cd_0.9(Li_1-xFe_x)_0.1O (x = 0.1, 0.3, 0.5, 0.7) with NaCl structure has been synthesized using formate of the composition Cd_0.9(Li_1-xFe_x)_0.1(HCOO)₂·2H₂O as a precursor. The NMR spectroscopy results demonstrate that the structure of lithium-doped cadmium oxide appears to have impurity centers only of one type. All the synthesized samples show a metal-like conductivity as indicated by the growth of their electrical resistance with temperature increasing in the interval 78–330 K. The study of the magnetic properties of the Cd_0.9(Li_1-xFe_x)_0.1O samples at 5 and 300 K revealed that they are ferromagnets, whose saturation magnetization increases with the iron concentration both at low and room temperature reaching the maximal values in the samples with a Li and Fe concentration of 3 and 7 at.%, respectively. An enhancement of the iron concentration in Cd_0.9(Li_1-xFe_x)_0.1O from x = 0.5 to x = 0.7 leads to an abrupt growth of the magnetization from 0.30 to 1.94 emu/g at 5 K and from 0.16 to 1.03 emu/g at 300 K. Iron doping with a simultaneous reduction of the lithium concentration also results in an increase of the band gap. The properties of these compounds are explained on the basis of first-principles calculations of their band structure.

CaCu₃Ti₄O₁₂ ceramics have great dielectric constant, excellent temperature stability and good frequency stability. However, due to high dielectric loss, its practical application in engineering is hindered. In this paper, Na_0.25Bi_0.25La_xCa_0.5-3x/2Cu₃Ti₄O₁₂ (NBLCCTO) ceramics were prepared by solid phase synthesis. The effects of sintering temperature and La content on dielectric properties of NBLCCTO ceramics were studied. The results show when the sintering temperature is 1030℃ and La content is 0.05, NBLCCTO ceramics show better dielectric properties. Its dielectric constant has ε_r = 22,231 at 1 kHz and its dielectric loss is 0.0546 at 10 kHz. Appropriate doping of La can lead to grain refinement and enlarge specific surface area of grain boundary, thus increasing resistivity and reducing dielectric loss. Therefore, NBLCCTO ceramics have lower dielectric loss than Na_0.25Bi_0.25Ca_0.5Cu₃Ti₄O₁₂ (NBCCTO).

NaNbO₃-based lead-free ceramics show great potential in energy storage and piezoelectric applications due to the antiferroelectric and ferroelectric features. However, pure NaNbO₃ usually shows lossy hysteresis loops because of the metastable antiferroelectric phase at room temperature. In this work, Bi(Zn_2/3Nb_1/3)O₃ was introduced into NaNbO₃ to modulate the phase structure, dielectric, and energy storage properties. The addition of Bi(Zn_2/3Nb_1/3)O₃ changed the phase structure from orthorhombic to pseudo-cubic, decreased the grain size from ~ 20 μm to ~ 1 μm, shifted the temperature of dielectric peak from 360℃ to room temperature, and led to much-reduced polarization hysteresis and improved breakdown strength. With the addition of 9 mol% Bi(Zn_2/3Nb_1/3)O₃, the maximum recoverable energy density of 3.3 J/cm³ was achieved under 33.5 kV/mm. These results provide a feasible route to design and fabricate new NaNbO₃-based energy storage ceramics.

A well-designed matching layer attached to a transducer is an effective method to obtain broad bandwidth. In practical applications, the optimal material parameters and geometric parameters for the matching layer are required to be calculated precisely. In this paper, we propose a fluid–structure interaction model for vibro-acoustic analysis of the transducer. An analytical solution to determine the electrical impedance of a transducer with a matching layer immersed in water is derived. The influence of matching layer on the performance of the transducer is demonstrated clearly. To verify the proposed model, a 1–3 piezoelectric composite transducer with a matching layer according to the our proposed model is fabricated. Consequently, the theoretical model we proposed can accurately predict the electrical impedance of the transducer with a matching layer. According to the model, the optimal thickness and acoustic impedance for the matching layer to expand the conductance bandwidth of the transducer can be figured out accurately. In addition, our proposed model also provides a reference for designing a transducer with a matching layer.

In this study Dy³⁺ doped Ca_6-xNa₂Y₂(SiO₄)₆(OH)₂ (x = 0 – 0.05 mol%) hydroxyapatite compound was synthesized by co – precipitation method. The structural analysis reveals that the prepared compound has single phase hexagonal structure with space group P6₃/m. Scanning electron microscopy images show that the grains have irregular morphology and the grain size lies between 120—800 nm. The dielectric and electrical conduction studies of hydroxyapatite compound was done over a wide range of frequency (10² – 10⁵ Hz) and temperature (50⁰C – 500⁰C) respectively. Dielectric measurement shows that orientational and space charge polarizations are the dominant polarization mechanisms. Complex impedance and electric modulus spectroscopy analysis shows that ionic conduction is the presiding conduction mechanism. Nyquist plots depict the contribution of grains rather than grain boundaries in the conduction phenomena. A.C conductivity analysis shows that hydroxyl (OH)⁻ and oxygen (O⁻²) ions were the main charge carriers responsible for conduction phenomena in hydroxyapatite compounds.

Nanocrystalline BiFeO₃ was synthesized utilizing two distinct techniques: auto-combustion and ceramic. A unique auto-combustion process employing glycine as a fuel has been used to synthesize single-phase BiFeO₃ nanoparticles. Well mixed metal nitrates combust, producing BiFeO₃ nanoparticles, which crystallize in a rhombohedral perovskite structure. The average particle size of 16 nm was estimated using Rietveld refinement of the X-ray diffraction data. The X-ray diffraction data for the solid-state prepared sample shows the formation of BiFeO₃ with the same rhombohedral perovskite structure with an average particle size of 101 nm with additional secondary phases corresponding to Bi₂Fe₄O₉/Bi₂O₃ and Bi₂₅FeO₃₉. By increasing the sintering time Bi₂Fe₄O₉/Bi₂O₃ phase disappeared after 3 h of heating and reappeared again after 5 h of sintering. The changing of sintering time was not able to reduce the Bi₂₅FeO₃₉ formation. The TEM estimated average particle size confirms the XRD analysis. M(H) hysteresis loop shows a G-type magnetic structure. Due to the small particle size, the periodicity of canted spins was broken, and the magnetization of the auto-combustion prepared sample is approximately eight times greater than the ceramic prepared one. The importance of pure phase BiFeO₃ came from its potential applications in sensors, data storage, spintronics devices, and reports of greatly enhanced ferroelectricity in epitaxially strained thin films.

The 1–3 connectivity epoxy resin modified cement based piezoelectric composites were developed to meet the requirement of concrete structural heath monitoring. The piezoelectric ceramic volume fraction on piezoelectric, dielectric and electromechanical coupling properties of the composites were discussed. The results showed that the relative permittivity of the piezoelectric composites increases linearly with increasing the PZT piezoelectric ceramic volume fraction, but the dielectric loss of the piezoelectric composites is a little bit larger than that of the PZT ceramic. The piezoelectric strain constant d₃₃ of the piezoelectric composites is mainly contributed by PZT ceramic and is in proportion to PZT volume fraction, however, the piezoelectric voltage constant ({g}_{33}) show the opposite variation. When PZT volume fraction decreases to 27.7%, ({g}_{33}) value of the piezoelectric composites reaches to 75.0 (mV)·m·N⁻¹_. When PZT ceramic volume fraction is 62.33%, the thickness electromechanical coupling coefficient k_t of the piezoelectric composites is the largest of 66.73%. The acoustic impedance Z of the piezoelectric composite is close to that of the concrete when PZT ceramic volume fraction is less than 44.44%.

In this research, hard/soft CoFe₂O₄/Ni magnetic nanocomposite samples with different concentrations of Ni were successfully produced by a two-step mechanical alloying route. Single-phase CoFe₂O₄ (CFO), having the average particle size of 35 nm, saturation magnetization of 71 emu/g, and bandgap energy of 2.6 eV was synthesized via the mechanical alloying method. A mixture of as-synthesized CFO and 10, 30 and, 50 wt. % Ni powder has been severely milled to prepare magnetic nanocomposite samples. The effects of different Ni content on the characteristics of the nanocomposite samples have been investigated. FESEM images showed that the ductile nickel powder particles get flattened after 1 h milling, whereas the brittle CFO particles get fragmented by increasing milling time to 10 h. The single-phase-like hysteresis loop, and the switching field distribution curves alongside the simultaneous enhancements of maximum energy product and remanence reflect the presence of exchange spring phenomenon in the nanocomposite samples. Also, the diffuse reflectance spectroscopy (DRS) analysis evidence the reduction of bandgap energy for 10 wt.% Ni containing nanocomposite sample from 2.44 to 2.15 eV on increasing the milling time from 1 to 10 h. Under the optimum photocatalyst operating conditions, the CFO/10 wt% Ni sample exhibited the highest photocatalytic activity of 93.6% for methylene blue (MB) degradation in comparison with the cobalt ferrite sample. Eventually, the detailed kinetic and mechanism to describe the improvement of the photocatalytic performance were suggested.

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Optical and photocatalytic applications of Al₂O₃ and TiO₂ ceramics are limited, especially under visible light, due to their wide bandgap; so, this parameter plays an important and even decisive role in these applications. In the present study, Al₂O₃-TiO₂ ball milled powders were sintered by spark plasma sintering (SPS) at 1573 K. The products were characterized using XRD, SEM, UV–Vis and electrochemical methods. The results indicated effective improvement in the light absorbing capability of the composites (up to 95%) under visible light and the decrease of the band gap down to 2.2 eV owing to the increase of oxygen vacancies, which was, in turn, due to the reduced atmosphere of the sintering process. In addition, formation of a new phase (Al₂TiO₅) during sintering greatly affected the absorption of Al₂O₃-TiO₂ composites in the visible light region due to the increase in the fraction of the charge carrier separation centers. Photo-luminescence spectroscopy also showed that tialite formation could be effective in improving the charge separation efficiency.

Piezoelectric nanogenerators (PENG) collect energy from the environment and biomechanical movements and convert this mechanical energy into electrical energy. They have become an attractive alternative to traditional rechargeable batteries for providing electrical power low energy portable devices. As PENGs became the center of attention in robots, wearable devices, medical equipment, and many other fields, the development of piezoelectric materials has become mandatory. This review reviews the basic information, structure, properties, and preparation methods of Barium Titanate, one of the most important PENGs, its development in recent years, and the progress towards high energy generation.