Colossal dielectric permittivity,reduced loss tangent and the microstructure of Ca1−xCdxCu3Ti4O12−2yF2y ceramics

Ca_1−xCd_xCu₃Ti₄O_12−2yF_2y (x = y = 0, 0.10, and 0.15) ceramics were successfully prepared via a conventional solid-state reaction (SSR) method. A single-phase CaCu₃Ti₄O₁₂ with a unit cell ∼7.393 Å was detected in all of the studied ceramic samples. The grain sizes of sintered Ca_1−xCd_xCu₃Ti₄O_12−2yF_2y ceramics were significantly enlarged with increasing dopant levels. Liquid-phase sintering mechanisms could be well matched to explain the enlarged grain size in the doped ceramics. Interestingly, preserved high dielectric permittivities, ∼36 279–38 947, and significantly reduced loss tangents, ∼0.024–0.033, were achieved in CdF₂ codoped CCTO ceramics. Density functional theory results disclosed that the Cu site is the most preferable location for the Cd dopant. Moreover, F atoms preferentially remained close to the Cd atoms in this structure. An enhanced grain boundary response might be a primary cause of the improved dielectric properties in Ca_1−xCd_xCu₃Ti₄O_12−2yF_2y ceramics. The internal barrier layer capacitor model could well describe the colossal dielectric response of all studied sintered ceramics.

CdF₂ defect clusters result in enhancement of dielectric properties of the Ca_1−xCd_xCu₃Ti₄O_12−2yF_2y ceramics.     

Catalytic oxidation of NO over MnOx–CoOx/TiO2 in the presence of a low ratio of O3/NO: activity and mechanism

In order to broaden the temperature range of NO oxidation reaction in flue gas and maintain high oxidation efficiency, various loading amounts of MnO_x–CoO_x/TiO₂ mesoporous catalysts were tested in the catalytic oxidation of NO. It was found that 15%MnO_x–CoO_x(2 : 1)/TiO₂ demonstrated the best adsorption performance to oxygen species and contained more oxygen vacancies, as well as the best surface oxygen mobility, thus exhibiting excellent NO catalytic oxidation activity. O₃ (O₃/NO < 1) combined with 15%MnO_x–CoO_x(2 : 1)/TiO₂ improved the oxidation efficiency of NO at 50–400 °C, especially below 250 °C. When the temperatures were less than 250 °C, the oxidation efficiencies of NO by O₃ over 15%MnO_x–CoO_x(2 : 1)/TiO₂ were 5–13% higher than the calculated theoretical efficiencies. This indicated that there was a synergistic effect between O₃ and 15%MnO_x–CoO_x(2 : 1)/TiO₂ below 250 °C. Based on the results of in situ DRIFTS studies, it was deduced that monodentate nitrates were the main intermediates that produced a synergistic effect due to the introduction of O₃. In addition, O₃ accelerated the transformation between nitrate species, decreased the decomposition temperature of nitrate species, and inhibited the accumulation of nitrate ions, thus improving the oxidation efficiency of NO.

O₃ promotes the formation of monodentate nitrates at low temperature, thus improving the efficiency of NO oxidation.     

Enhancing the thermoelectric power factor of nanostructured ZnCo2O4 by Bi substitution

Bi_xZnCo_2−xO₄ (0 ≤ x ≤ 0.2) nanoparticles with different x values have been prepared by the sol–gel method; the structural, morphological, thermal and thermoelectric properties of the prepared nanomaterials are investigated. XRD analysis confirms that Bi is completely dissolved in the ZnCo₂O₄ lattice till the x values of ≤0.1 and the secondary phase of Bi₂O₃ is formed at higher x value (x > 0.1). The synthesized nanomaterials are densified and the thermoelectric properties are studied as a function of temperature. The electrical resistivity of the Bi_xZnCo_2−xO₄ decreased with x value and it fell to 4 × 10⁻² Ω m for the sample with x value ≤ 0.1. The Seebeck coefficient value increased with the increase of Bi substitution till the x value of 0.1 and decreased for the sample with higher Bi content (x ≤ 0.2) as the resistivity of the sample increased due to secondary phase formation. With the optimum Seebeck coefficient and electrical resistivity, Bi_0.1ZnCo_1.9O₄ shows the high-power factor (α²σ_{550 K}) of 2.3 μW K⁻² m⁻¹ and figure of merit of 9.5 × 10⁻⁴ at 668 K respectively, compared with other samples. The experimental results reveal that Bi substitution at the Co site is a promising approach to improve the thermoelectric properties of ZnCo₂O₄.

Nanostructuring and Bi substitution have considerably increased the thermoelectric power factor and ZT of Bi_xZnCo_2−xO₄; Bi_1.9ZnCo_1.9O₄ shows a higher power factor than that of other Bi substituted samples.     

Microwave dielectric properties of low-temperature-fired MgNb2O6 ceramics for LTCC applications

MgNb₂O₆ ceramics doped with (Li₂O–MgO–ZnO–B₂O₃–SiO₂) glass were synthesized by the traditional solid phase reaction route. The effects of LMZBS addition on microwave dielectric properties, grain growth, phase composition and morphology of MgNb₂O₆ ceramics were studied. The SEM results show dense and homogeneous microstructure with grain size of 1.72 μm. Raman spectra and XRD patterns indicate the pure phase MgNb₂O₆ ceramic. The experimental results show that LMZBS glass can markedly decrease the sintering temperature from 1300 °C to 925 °C. Higher density and lower porosity make ceramics have better dielectric properties. The MgNb₂O₆ ceramic doped with 1 wt% LMZBS glass sintered at 925 °C for 5 h, possessed excellent dielectric properties: ε_r = 19.7, Q·f = 67 839 GHz, τ_f = −41.01 ppm °C⁻¹. Moreover, the favorable chemical compatibility of the MgNb₂O₆ ceramic with silver electrodes makes it as promising material for low temperature co-fired ceramic (LTCC) applications.

MgNb₂O₆ ceramics doped with (Li₂O–MgO–ZnO–B₂O₃–SiO₂) glass were synthesized by the traditional solid phase reaction route.     

Effect of the itinerant electron density on the magnetization and Curie temperature of Sr2FeMoO6 ceramics

The itinerant electron density (n) near the Fermi level has a close correlation with the physical properties of Sr₂FeMoO₆. Two series of single-phase Sr_(2−y)Na_yFeMoO₆ (y = 0.1, 0.2, 0.3) and Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆ (y = 2x; y = 0.1, 0.2, 0.3) ceramics were specially designed and the itinerant electron density (n) of them can be artificially controlled to be: n = 1 − y and n = 1 − y + 3x = 1 + 0.5y, respectively. The corresponding crystal structure, magnetization and the ferromagnetic Curie temperature (T_C) of two subjects were investigated systematically. The X-ray diffraction analysis indicates that Sr_(2−y)Na_yFeMoO₆ (y = 0.1, 0.2, 0.3) have comparable Fe/Mo anti-site defect (ASD) content in spite of decreased n. However, a drastically improved Fe/Mo ASD can be observed in Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆ (y = 2x; y = 0.1, 0.2, 0.3) caused by the intrinsic wrong occupation of normal Fe sites with excess Mo. Magnetization–magnetic field (M–H) behavior confirms that it is the Fe/Mo ASD not n that dominantly determines the magnetization properties. Interestingly, approximately when n ≤ 0.9, T_C of Sr_(2−y)Na_yFeMoO₆ (y = 0.1, 0.2, 0.3) exhibits an overall increase with decreasing n, which is contrary to the T_C response in electron-doped SFMO. Such abnormal T_C is supposed to relate with the ratio variation of n(Mo)/n(Fe). Moreover, when n ≥ 1, T_C of Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆ (y = 2x; y = 0.3) exhibits a considerable rise of about 75 K over that of Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆ (y = 2x; y = 0.1), resulting from improved n caused by introducing excess Mo into Sr_(2−y)Na_yFeMoO₆. Maybe, our work can provide an effective strategy to artificially control n and ferromagnetic T_C accordingly, and provoke further investigation on the FeMo-baseddouble perovskites.

T _C of C6 exhibits a significant rise of 75 K over that of C2, resulting from introducing excess Mo in Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆.     

Preparation and heat-insulating properties of Al2O3–ZrO2(Y2O3) hollow fibers derived from cogon using an orthogonal experimental design

Bionic design is efficient to develop high-performance lightweight refractories with sophisticated structures such as hollow ceramic fibers. Here, we report a four-stage procedure for the preparation of Al₂O₃–ZrO₂(Y₂O₃) hollow fibers using the template of cogon—a natural grass. Subsequently, to optimize the thermal performance of the fibers, four sets of preparation parameters, namely, x(Al₂O₃), solute mass ratio of the mixture, dry temperature, and sintering temperature were investigated. Through an orthogonal design, the optimal condition of each parameter was obtained as follows: x(Al₂O₃) was 0.70, solute mass ratio of the mixture was 15 wt%, dry temperature was 80 °C, and sintering temperature was 1100 °C. Overall, Al₂O₃–ZrO₂(Y₂O₃) hollow fibers show relatively low thermal conductivity (0.1038 W m⁻¹ K⁻¹ at 1000 °C), high porosity (95.0%), and low density (0.05–0.10 g cm⁻³). The multiphase compositions and morphology of Al₂O₃–ZrO₂(Y₂O₃) hollow fibers, which may contribute to their thermal properties, were also discussed.

Lightweight Al₂O₃–ZrO₂(Y₂O₃) hollow fibers with low thermal conductivity were prepared by a natural template—cogon grass.     

Dielectric and photoluminescence properties of fine-grained BaTiO3 ceramics co-doped with amphoteric Sm and valence-variable Cr

(Ba_1−xSm_x)(Ti_1−xCr_x)O₃ (BSTC) and (Ba_1−xSm_x)(Ti_{1−(x−0.01)}Cr_x−0.01)O₃ (BSTC1) ceramics with a single-phase perovskite structure were prepared using a traditional solid state based method. The structure, microstructure, site occupations, valence states of Cr, photoluminescence, and dielectric properties of these ceramics were investigated using XRD, SEM, EDXS, RS, EPR, XPS, and dielectric measurements. All ceramics exhibit a fine-grained microstructure (0.7 μm). Three valence states of Cr ions were confirmed and Cr predominates as Cr³⁺ enter the Ti⁴⁺ sites with a stronger EPR signal (1.974). The RS bands of high-wavenumber were attributed to photoluminescence from Sm³⁺ ions. The formation of defect complexes play leading roles in the removal of prevent the grain growth, and photoluminescence quenching. (Ba_1−xSm_x)(Ti_{1−(x−0.01)}Cr_x−0.01)O₃ (BSTC1) ceramics with amphoteric Sm³⁺ ions exhibit a regular diffuse phase transition behavior, rapid T_m-shifting rate of −24.3 °C/at% (Sm/Cr), higher lower tan δ and x = 0.04 and 0.05 met the EIA Y5V specification.

(Ba_1−xSm_x)(Ti_1−xCr_x)O₃ (BSTC) and (Ba_1−xSm_x)(Ti_{1−(x−0.01)}Cr_x−0.01)O₃ (BSTC1) ceramics with a single-phase perovskite structure were prepared using a traditional solid state based method.     

Single crystal growth and structure analysis of type-I (Na/Sr)–(Ga/Si) quaternary clathrates

Single crystals of (Na/Sr)–(Ga/Si) quaternary type-I clathrates, Na_8−ySr_yGa_xSi_46−x, were synthesized by evaporating Na from a mixture of Na–Sr–Ga–Si–Sn in a 6 : 0.5 : 1 : 2 : 1 molar ratio at 773 K for 12 h in an Ar atmosphere. Electron-probe microanalysis and single-crystal X-ray diffraction revealed that three crystals from the same product were Na_8−ySr_yGa_xSi_46−x with x and y values of 7.6, 2.96; 8.4, 3.80; and 9.1, 4.08. It was also shown that increasing the Sr and Ga contents increased the electrical resistivity of the crystal from 0.34 to 1.05 mΩ cm at 300 K.

Single crystals of (Na/Sr)–(Ga/Si) quaternary type-I clathrates, Na_8−ySr_yGa_xSi_46−x, were synthesized by evaporating Na from a mixture of Na–Sr–Ga–Si–Sn in a 6 : 0.5 : 1 : 2 : 1 molar ratio at 773 K for 12 h in an Ar atmosphere.     

Copper–cobalt catalysts supported on mechanically mixed HZSM-5 and γ-Al2O3 for higher alcohols synthesis via carbon monoxide hydrogenation

Mechanically mixed γ-Al₂O₃ and HZSM-5 (Si/Al = 50) with different mass ratio were utilized as support for Cu–Co higher alcohol synthesis catalysts prepared through incipient wetness impregnation. The textural and structural properties were studied using Ar low temperature adsorption and desorption, H₂-temperature programmed reduction (H₂-TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and catalytic performance measurements. The results indicated that the mechanically mixed HZSM-5 and γ-Al₂O₃ supported copper–cobalt catalysts were superior to either γ-Al₂O₃ or HZSM-5 supported ones with the same metal loading. The results revealed that using HZSM-5 and γ-Al₂O₃ mechanically mixed benefited the dispersion of metallic phases and stronger synergetic functions between smaller nanoparticles containing copper and/or cobalt, which is essential for HAS from CO hydrogenation. Under working conditions of P = 5.0 MPa, T = 300 °C, V(H₂) : V(CO) : V(N₂) = 4 : 2 : 1 and GHSV = 7200 mL g⁻¹ h⁻¹, mechanically mixed HZSM-5 and γ-Al₂O₃ supported catalysts showed higher catalytic activity than those over single support. For CuCo catalysts upon support containing 50.0 wt% HZSM-5 and 50.0 wt% γ-Al₂O₃, the CO conversion was 21.3% and the C₂₊ alcohol selectivity was 41.8%.

CuCo bimetallic catalysts over the mixed supports showed smaller average particle size, better dispersion of cobalt and copper species, and good activity for higher alcohols synthesis.     

Enhanced ferroelectric and piezoelectric performance of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead-free ceramics upon Ce and Sb co-doping

(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9−xCe_x)O₃+ySb (abbreviated as BCZTC_xS_y) ceramics were prepared by the conventional solid-state reaction. The effect of the co-doping of Ce and Sb on the phase structure, microstructure, dielectric, and ferroelectric and piezoelectric performances of BCZTC_xS_y ceramics were investigated systematically. The results indicated that the obtained ceramics are composed of coexisting rhombohedral and tetragonal phases. Significant improvements were also observed in the growth of grain, relative density, as well as electrical performance. After co-doping 0.05 mol% Ce and 0.10 mol% Sb, the sizes of crystalline grains reached the maximum. The following optimal properties were obtained: ε_r = 2353, tan δ = 0.026, T_c = 109.4 °C, P_max = 17.65 μC cm⁻², P_r = 10.43 μC cm⁻², E_c = 2.88 kV cm⁻¹, S_max = 0.125%, = 417 pm V⁻¹, d₃₃ = 372 pC N⁻¹. With the increase in dopants, the diffuseness γ increased from 1.663 to 1.733, indicating a more relaxed ferroelectric characteristic. All improvements show that BCZT ceramics co-doped with Ce and Sb could be promising candidates in lead-free devices.

(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9−xCe_x)O₃+ySb ceramics prepared by the conventional solid-state reaction.     

Structure of bismuth tellurite and bismuth niobium tellurite glasses and Bi2Te4O11 anti-glass by high energy X-ray diffraction

Glass and anti-glass samples of bismuth tellurite (xBi₂O₃–(100 − x)TeO₂) and bismuth niobium tellurite (xBi₂O₃–xNb₂O₅–(100 − 2x)TeO₂) systems were prepared by melt-quenching. The bismuth tellurite system forms glasses at low Bi₂O₃ concentration of 3 to 7 mol%. At 20 mol% Bi₂O₃, the glass forming ability of the Bi₂O₃–TeO₂ system decreases drastically and the anti-glass phase of monoclinic Bi₂Te₄O₁₁ is produced. Structures of glass and the anti-glass Bi₂Te₄O₁₁ samples were studied by high-energy X-ray diffraction, reverse Monte Carlo simulations and Rietveld Fullprof refinement. All glasses have short short-range disorder due to the existence of at least three types of Te–O bonds of lengths: 1.90, 2.25 and 2.59 Å, besides a variety of Bi–O and Nb–O bond-lengths. The medium-range order in glasses is also disturbed due to the distribution of Te–Te pair distances. The average Te–O co-ordination (N_Te–O) in the glass network decreases with an increase in Bi₂O₃ and Nb₂O₅ mol% and is in the range: 4.17 to 3.56. The anti-glass Bi₂Te₄O₁₁ has a long-range order of cations but it has vibrational disorder and it exhibits sharp X-ray reflections but broad vibrational bands similar to that in glasses. Anti-glass Bi₂Te₄O₁₁ has an N_Te–O of 2.96 and is significantly lower than in glass samples.

Te–O, Bi–O and Nb–O bond lengths, co-ordinations in bismuth tellurite, bismuth niobium tellurite glasses and Bi₂Te₄O₁₁ anti-glass by HEXRD, RMC and Riteveld analysis.     

Studies on structural,dielectric and optical properties of (Ba0.95Ca0.05)1−x(Ti0.8Sn0.2)1−xNaxNbxO3 lead-free ceramics

(Ba_0.95Ca_0.05)_1−x(Ti_0.8Sn_0.2)_1−xNa_xNb_xO₃ (BCNTSNO₃) lead-free ceramics with compositions (x = 0.75, 0.8 and 0.85) were synthesized through the traditional solid-state reaction method. X-ray powder diffraction analysis showed the formation of a single phase compound crystallized in tetragonal space group P4mm. The evolution of Raman spectra displayed a disorder introduced into the structure, which favors a ferroelectric relaxor behavior. The dependence of the dielectric properties on temperature exhibited two composition ranges with different behaviors. Ferroelectric relaxor properties were observed for the compositions x < 0.85 and the classical ferroelectric behavior for x = 0.85. Lead free (Ba_0.95Ca_0.05)_1−x(Ti_0.8Sn_0.2)_1−xNa_xNb_xO₃ ceramics exhibited larger dielectric constants than those of parent crystal NaNbO₃, suggesting that it is a good candidate for lead-free ceramics in several industrial applications. Using UV-Vis spectroscopy, the optical band gap energy of ceramics (Ba_0.95Ca_0.05)_1−x (Ti_0.8Sn_0.2)_1−xNa_xNb_xO₃ is found at 2.89, 2.92, and 3.05 eV for x = 0.75, 0.8 and 0.85, respectively.

(Ba_0.95Ca_0.05)_1−x(Ti_0.8Sn_0.2)_1−xNa_xNb_xO₃ (BCNTSNO₃) lead-free ceramics with compositions (x = 0.75, 0.8 and 0.85) were synthesized through the traditional solid-state reaction method.     

Structure,dielectric, and piezoelectric properties of K0.5Na0.5NbO3-based lead-free ceramics

Lead-free ceramics based on the (1 − x)K_0.5Na_0.5NbO₃–xBi(Zn_0.5Ti_0.5)O₃ (KNN–BZT) system obtained via the conventional solid-state processing technique were characterized for their crystal structure, microstructure, and electrical properties. Rietveld analysis of X-ray diffraction data confirmed the formation of a stable perovskite phase for Bi(Zn_0.5Ti_0.5)O₃ substitutions up to 30 mol%. The crystal structure was found to transform from orthorhombic Amm2 to cubic Pm$\bar{3}$m through mixed rhombohedral and tetragonal phases with the increase in Bi(Zn_0.5Ti_0.5)O₃ content. Temperature-dependent dielectric behavior indicated an increase in diffuseness of both orthorhombic to tetragonal and tetragonal to cubic phase transitions as well as a gradual shift towards room temperature. The sample with x ≈ 0.02 exhibited a mixed rhombohedral and orthorhombic phase at room temperature. A high-temperature X-ray diffraction study confirmed the strong temperature dependence of the phase coexistence. The sample with the composition 0.98(K_0.5Na_0.5NbO₃)–0.02(BiZn_0.5Ti_0.5O₃) showed an improved room temperature piezoelectric coefficient d₃₃ = 109 pC/N and a high Curie temperature T_C = 383 °C.

Room temperature powder X-ray diffraction patterns of (1 – x)K_0.5Na_0.5NbO₃–xBi(Zn_0.5Ti_0.5)O₃ system.     

Efficient in situ generation of H2O2 by novel magnesium–carbon nanotube composites

Hydrogen peroxide (H₂O₂) is widely employed as an environmentally friendly chemical oxidant and an energy source. In this study, a novel magnesium–carbon nanotube composite was prepared by a ball milling process in argon atmosphere using polyvinylidene fluoride (PVDF) as a binder. The resulting material was then tested for the in situ generation of H₂O₂. The preparation and operation conditions of the composite were systemically investigated and analyzed to improve the efficiency of the in situ generation of H₂O₂. Under the optimized conditions, while aerating with oxygen for 60 min, a maximum H₂O₂ concentration of 194.73 mg L⁻¹ was achieved by the Mg–CNTs composite prepared using Mg : CNT : PVDF with a weight ratio of 5 : 1 : 2.4. In the Mg–CNTs/O₂ system, dissolved oxygen molecules were reduced to H₂O₂, while magnesium was oxidized owing to the electrochemical corrosion. In addition, a part of dissolved magnesium ions converted into magnesium hydroxide and precipitated as nanoflakes on the surfaces of CNTs. A mechanism was proposed, suggesting that the formation of a magnesium/carbon nanotubes corrosion cell on the Mg–CNT composite promoted the in situ synthesis of H₂O₂. Overall, this study provides a promising and environmentally friendly strategy to fabricate magnesium/CNT composites for the in situ generation of H₂O₂, which could be applied in energy conversion and advanced oxidation processes for refractory wastewater treatment.

Mg–CNTs composite prepared by ball milling with PVDF promoted the in situ synthesis of H₂O₂.     

A novel resource utilization method using wet magnesia flue gas desulfurization residue for simultaneous removal of ammonium nitrogen and heavy metal pollutants from vanadium containing industrial wastewater

In the present study, a novel resource utilization method using wet magnesia flue gas desulfurization (FGD) residue for the simultaneous removal of ammonium nitrogen (NH₄–N) and heavy metal pollutants from vanadium (V) industrial wastewater was proven to be viable and effective. In this process, the wet magnesia FGD residue could not only act as a reductant of hexavalent chromium [Cr(vi)] and pentavalent vanadium [V(v)], but also offered plenty of low cost magnesium ions to remove NH₄–N using struvite crystallization. The optimum experimental conditions for Cr(vi) and V(v) reduction are as follows: the reduction pH = 2.5, the wet magnesia FGD residue dose is 42.5 g L⁻¹, t = 15.0 min. The optimum experimental conditions for NH₄–N and heavy metal pollutants removal are as follows: the precipitate pH = 9.5, the n(Mg²⁺) : n(NH₄⁺) : n(PO₄³⁻) = 0.3 : 1.0 : 1.0, t = 20.0 min. Finally the NH₄–N, V and Cr were separated from the vanadium containing industrial wastewater by forming the difficult to obtain, soluble coprecipitate containing struvite and heavy metal hydroxides. The residual pollutant concentrations in the wastewater were as follows: Cr(vi) was 0.047 mg L⁻¹, total Cr was 0.1 mg L⁻¹, V was 0.14 mg L⁻¹, NH₄–N was 176.2 mg L⁻¹ (removal efficiency was about 94.5%) and phosphorus was 14.7 mg L⁻¹.

A novel resource utilization method using wet magnesia flue gas desulfurization residue for the simultaneous removal of ammonium nitrogen and heavy metal pollutants from vanadium industrial wastewater was proven to be viable and effective.     

The rapid microwave-assisted hydrothermal synthesis of NASICON-structured Na3V2O2x(PO4)2F3−2x (0 < x ≤ 1) cathode materials for Na-ion batteries

NASICON-structured Na₃V₂O_2x(PO₄)₂F_3−2x (0 < x ≤ 1) solid solutions have been prepared using a microwave-assisted hydrothermal (MW-HT) technique. Well-crystallized phases were obtained for x = 1 and 0.4 by reacting V₂O₅, NH₄H₂PO₄, and NaF precursors at temperatures as low as 180–200 °C for less than 15 min. Various available and inexpensive reducing agents were used to control the vanadium oxidation state and final product morphology. The vanadium oxidation state and O/F ratios were assessed using electron energy loss spectroscopy and infrared spectroscopy. According to electron diffraction and powder X-ray diffraction, the Na₃V₂O_2x(PO₄)₂F_3−2x solid solutions crystallized in a metastable disordered I4/mmm structure (a = 6.38643(4) Å, c = 10.62375(8) Å for Na₃V₂O₂(PO₄)₂F and a = 6.39455(5) Å, c = 10.6988(2) Å for Na₃V₂O_0.8(PO₄)₂F_2.2). With respect to electrochemical Na⁺ (de)insertion as positive electrodes (cathodes) for Na-ion batteries, the as-synthesized materials displayed two sloping plateaus upon charge and discharge, centered near 3.5–3.6 V and 4.0–4.1 V vs. Na⁺/Na, respectively, with a reversible capacity of ∼110 mA h g⁻¹. The application of a conducting carbon coating through the surface polymerization of dopamine with subsequent annealing at 500 °C improved both the rate capability (∼55 mA h g⁻¹ at a discharge rate of 10C) and capacity retention (∼93% after 50 cycles at a discharge rate of C/2).

NASICON-structured Na₃V₂O_2x(PO₄)₂F_3−2x (0 < x ≤ 1) solid solutions have been prepared using a microwave-assisted hydrothermal (MW-HT) technique.     

Fatigue endurance enhancement of Sn-doped Pb(Lu1/2Nb1/2)O3–PbTiO3 ceramics

Several mechanisms and methods have been proposed to study the nature of electric fatigue in ferroelectric materials with perovskite structure, including defect agglomeration, field screening and the reorientation of defect dipoles. To ascertain the effect of defect, defect dipoles in particular on the fatigue behavior in perovskite ferroelectrics, 0.51Pb(Lu_1/2Nb_1/2)O₃–0.49PbTi_1−xSn_xO₃ ferroelectric ceramics were fabricated in this work. It is found that the fatigue endurance has been enhanced after Sn-doping. An abnormal strong self-rejuvenation of polarization was also detected for un-poled and un-aged samples resulting from the reorientation of defect dipoles. The defect dipoles were determined by the confirmed change of the valence of Sn ions and the appearance of oxygen vacancies. The reorientation was also confirmed by the internal bias of P–E hysteresis loops during the fatigue process. With more Sn doped into the matrix, the symmetry changed from a coexistence of rhombohedral and tetragonal phase to a rhombohedral phase. The remnant polarization decreased, while the coercive field first decreased then increased as x increased, which resulted from the composition variance and the effect of defect dipoles. It indicates that the defect dipoles play an important role in the electric fatigue behavior of Sn-doping PLN–PT ceramics.

Fatigue endurance has been enhanced of Sn-doped Pb(Lu_1/2Nb_1/2)O₃–PbTiO₃ ceramics, exhibiting an abnormal self-rejuvenation of remnant polarization.     

Improved electrical transport properties of polycrystalline La0.8(Ca0.12Sr0.08)MnO3 ceramics by Ag2O doping

Polycrystalline La_0.8(Ca_0.12Sr_0.08)MnO₃:mol%Ag_x (LCSMO:Ag_x, x = 0, 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized by the sol–gel technique. Structural, electrical and magnetic properties of the LCSMO:Ag_x ceramics were investigated in detail. X-ray diffraction (XRD) data analyses revealed that all the samples were crystalized in the orthorhombic structure with space group of Pnma. With the increase in Ag doping (x), the grain sizes of the LCSMO:Ag_x samples increased and the amount of grain boundaries (GBs) decreased accordingly. At the same time, the Mn–O bond distance and the Mn–O–Mn bond angles changed correspondingly, leading to the slight increase in the lattice constants (a, b and c) and slight expansion of cell volume (V). For the LCSMO:Ag_x sample with x = 0.3, the optimal values of temperature coefficient of resistivity (TCR) and magnetoresistance (MR) reached 16.22% K⁻¹ (265.1 K) and 42.07% K⁻¹ (270.48 K), respectively. In addition, the fitting analysis of ρ–T curves showed that the experimental data were consistent with the theoretical calculation data. In the T < T_MI (metal-insulator transition temperature) region, the electrical conduction mechanism of LCSMO:Ag_x was clarified by electron-magnon, electron–electron and electron-phonon scattering. In the T > T_MI region, the resistivity data were interpreted by using the adiabatic small-polaron hopping model. Furthermore, in the entire temperature range, the phenomenological equation called the percolation model was used to explain the resistivity data and the phase-separation mechanism of ferromagnetic metallic (FM) and paramagnetic insulating (PI) phases. All the obtained results indicated that the improvement in the electrical properties of the LCSMO:Ag_x samples was attributed to the doping of Ag, which changed the A-site (La, Ca and Sr ions) average ion radius, the Mn–O–Mn bond angles and the Mn–O bond distance. In addition, the grain size increased, which led to improvement in the Mn⁴⁺ ion concentration and the GBs connectivity in the LCSMO:Ag_x polycrystalline ceramics.

Polycrystalline La_0.8(Ca_0.12Sr_0.08)MnO₃:mol%Ag_x (LCSMO:Ag_x, x = 0, 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized by the sol–gel technique.     

Structural and morphological studies,and temperature/frequency dependence of electrical conductivity of Ba0.97La0.02Ti1−xNb4x/5O3 perovskite ceramics

Conductivity measurements of our polycrystalline perovskite ceramic systems with a composition of Ba_0.97La_0.02Ti_1−xNb_4x/5O₃ (x = 5, 7 and 10, in mol%) were performed, in order to investigate frequency and temperature dependence. Our ferroelectric ceramics were fabricated by the molten-salt method (chemical reaction followed by an evaporation and filtration reaction); X-ray diffraction patterns indicated that a single phase was formed for pure BaLT_1−xNb_4x/5 ceramics. The electrical behavior of the ceramics was studied by impedance spectroscopy in the 500–610 K temperature range. The conductivity was investigated which can be described by the Jonscher law. Both AC and DC electrical conductivities are completely studied as a function of frequency and temperature. The conductivity exhibits a notable increase with increasing Nb-rates. The low-frequency conductivity results from long-range ordering (close to frequency-independent) and the high-frequency conductivity is attributable to the localized orientation hopping process. Impedance analysis was performed revealing conductivity data which fitted the modified power, σ_AC(ω) = Aωⁿ. The frequency dependence of the conductivity plot has been found to obey the universal Jonscher power law. Both AC and DC electrical conductivities are thoroughly studied as a function of frequency as well as temperature. The AC conductivity reveals that correlated barrier hopping (CBH) and non-overlapping small polaron tunneling (NSPT) models are suitable theoretical models to elucidate the conduction mechanisms existing in our compounds. Significantly, by increasing the temperature, the DC conductivity was increased, which verifies the semiconducting nature of the materials.

The frequency- and temperature-dependent conductivity of our polycrystalline perovskite ceramic systems with a composition of Ba_0.97La_0.02Ti_1−xNb_4x/5O₃ (x = 5, 7 and 10, in mol%) was investigated.     

Investigation of BaO reinforced TiO2–p2O5–li2O glasses for optical and neutron shielding applications

The optical and radiation shielding characteristics of 15TiO₂-70P₂O₅ – (15 − x) Li₂O-x BaO x = (0 ≤ x ≤ 10 mol%) glasses were reported in this study. The glass status of the investigated samples was established by XRD. Although the molar volume decreases within 39.8–31.2 cm³ mol⁻¹, the density was increased from 2.908 to 4.11 g cm⁻³ with the addition of BaO. UV-Vis-NIR spectroscopy was utilized for the examination of the optical characteristics of all compositions. E^indir_opt. and E^dir_opt. both increased from 2.7 to 3.07 eV and 2.79 to 3.31 eV, while E_u decreased from 0.368 to 0.295 eV. Furthermore, the Phy-X/PSD code was used to evaluate the gamma-ray shielding parameter. Within the energy range of 15 keV to 15 MeV, the equivalent atomic number, as well as the EBF and EABF parameters, was evaluated. Overall, excellent material properties were detected for a glass with a high BaO content, which could be useful for future optical, shielding, and fast neutron shielding properties.

The optical and radiation shielding characteristics of 15TiO₂–70P₂O₅ – (15 − x) Li₂O-x BaO x = (0 ≤ x ≤ 10 mol%) glasses were reported in this study.