Dielectric properties of Erbium doped CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> prepared by sol–gel self combustion method

The dielectric properties of Erbium doped CaCu₃Ti_(4–x)Er_xO_(12–δ) with x = 0, 0.05, 0.1 were synthesized by the sol–gel self combustion method. XRD (X-ray powder diffraction) analysis confirmed the formation of single-phase material in the samples calcined at 800 °C. Crystal structure does not change on doping with Erbium and it remains cubic in all the three compositions studied. It is found that lattice parameter increases slightly with Erbium doping. The surface morphology of CaCu₃Ti_(4–x)Er_xO_(12–δ) powders sintered at 950 °C in air for 3 h was observed using high resolution—scanning electron microscope and it shows that the grain size is in the range of 1–8 μm for these samples. Energy dispersive X-ray spectroscopy pattern confirmed the presence of Erbium with 1.9 and 4.86 atomic percentages with doping concentration. The dielectric characteristics of CaCu₃Ti_(4–x)Er_xO_(12–δ) were studied by LCR meter in the frequency range (100 Hz–1 MHz) at various temperatures (RT to 500 °C). Interestingly, the dielectric constant increases and dielectric loss had lower values than those of undoped CCTO.     

Investigation of charge transport mechanism in semiconducting La<Subscript>0.5</Subscript>Ca<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>O<Subscript>3</Subscript> manganite prepared by sol–gel method

Here in, we report the charge transport mechanism in semiconducting La_0.5Ca_0.5Mn_0.5Fe_0.5O₃ (LCMFO) polycrystalline material synthesized via sol–gel auto combustion route. X-ray diffraction (XRD) analysis confirmed the orthorhombic phase of the prepared material. Temperature dependent resistivity and impedance spectroscopy measurements have been carried out to probe the dielectric and electrical conduction mechanism which revealed a change of Mott variable range to the small polaronic hopping conduction mechanism around 303 K. The complex impedance and modulus spectra undoubtedly showed the contribution of both grain and grain boundary effect on the conduction properties of LCMFO. An equivalent circuit [(R_gbQ_gb) (R_gQ_g)] model has been used to address the electrical parameters associated with the different phases (grains and grain boundaries) having different relaxation times. The values of resistances of two phases obtained after fitting the equivalent circuit in the nyquist plot have been analyzed which confirmed the change of conduction mechanism around 303 K. The resultant change in conduction mechanism is also supported by the conductivity plots.     

Synthesis and piezoelectric properties of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> ceramics prepared by sol–gel auto-combustion method

In this study, NaNO₃, Bi(NO₃)₃·5H₂O, Ba(NO₃)₂, Ti(OC₄H₉)₄ and citric acid were successfully introduced to fabricate lead-free piezoelectric (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ [NBBT] nanopartical powders by a novel modified sol–gel auto-combustion method. The resultant products were characterized by the X-ray diffraction analysis and transmission electron microscope method. (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ + Mn(NO₃)₂ [NBBTM] can be sintered by the traditional solid-state reaction, and the effects of NBBT doped different amounts of Mn(NO₃)₂ at various sintering temperatures upon phase formation, microstructure as well as piezoelectric properties were further studied. The experimental results show that it was helpful to control their chemical ingredients and microstructure to prepare nanocrystalline single phase NBBT powders. Where is the X-ray diffraction result of the corresponding ceramics to prove the existence of the mixing between rhombohedral and tetragonal phases at the MPB compositions. Doping 0.015 mol% Mn(NO₃)₂ into NBBT at 1,090 °C, piezoelectric constant (d ₃₃) and relative dielectric constant (ε_r) reach the superior value of 159pC/N and 1,304, respectively, and dielectric loss (tan δ) and electromechanical coupling factor (K _t) are 2.5% and 65%, respectively.     

Synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powder via PVA assisted sol–gel process

CoFe₂O₄ ferrites were synthesized by sol–gel method, having metal nitrates as precursors and PVA as surfactant, followed by a heat treatment at 960 °C for 2 h. The ultrafine ferrite powders obtained have been characterized by X-ray diffraction, thermal gravimetry, differential scanning calorimetry and room temperature magnetic measurement studies. The morphology of the powder was identified by high resolution-scanning electron microscopy. X-ray diffraction results indicate that the resultant CoFe₂O₄ crystallites consist of spinel phase. Significant differences in magnetic properties of CoFe₂O₄ samples synthesized with various concentrations of PVA were observed. The magnetisation measurements show that when the PVA concentration increased, coercivity initially decreased and then increased where as retentivity and magnetisation decreased. The optimum concentration of PVA for the synthesis of CoFe₂O₄ ferrites is obtained from this investigation. Obviously this material can be used as an efficient candidate for practical recording purpose.     

Conversion reaction mechanisms of cubic bismuth phosphate Bi<Subscript>13.1</Subscript>PO<Subscript>δ</Subscript> as cathode in lithium-ion batteries

Compounds containing bismuth ions (Bi³⁺) as cathodes used in lithium-ion batteries based on chemical conversion reaction were supposed to be the most promising cathodes. They were considered to break through the storage capacity because a Bi atom could react with three Li⁺ ions and simultaneously transfer three electrons at a time during conversion reaction. In the paper, the cubic phase bismuth phosphate Bi_13.1PO_δ as cathode used in lithium-ion batteries was proposed. The results showed that the crystalline Bi_13.1PO_δ with sizes of 2–5 μm synthesized via hydrothermal method possessed excellent capacities and poor cycling stability. The initial discharge and charge capacities reached to 706 and 419 mAh g^?1 at current density of 39.06 mA g^?1. To improve the cycling stability of the cathode material, the chemical conversion process was focused on investigation. The elemental analyses indicated that the ratio of Bi:P ratio was decreased from 12.98 to 4.00, which suggests that about 8 Bi atoms participated in the reaction. Therefore, the capacities of the material were very high. The reduced Bi transformed from the beginning isolated state to ribbon or plate one, and coated on the surface of the active materials, inhibiting further conversion reaction. Consequently, the cycling stability of the cathode material was less than the capacity performance.     

The microwave absorbing properties of La<Subscript>0.8</Subscript>K<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript> synthesized by sol–gel method

In this paper, La_0.8K_0.2MnO₃ powder was synthesized by sol–gel method. The phase structure, morphology of the composite have been characterized by X-ray diffraction, field emission scanning electron microscope. Testing of the microwave absorption was carried out by using the network analyzer Agilent HP-8722ES at room temperature. The results show that the La_0.8K_0.2MnO₃ powder has excellent absorbing property. The maximum reflection loss is ?33.51 dB at about 12.22 GHz with a thickness of only 1.25 mm. Moreover, the bandwidth with the reflection loss above 10 dB reaches about 2.1 GHz.     

Comparison study on magnetic property of Co<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> powders by template-assisted sol–gel and hydrothermal methods

The nickel cobalt ferrite (Co_0.5Zn_0.5Fe₂O₄) nanopowders were synthesized by a sol–gel method and a hydrothermal method. Polyethylene glycol (PEG-4000) and carboxymethyl cellulose (CMC) were used as the templating agents for controlling the anisotropy and the microstructure of the Co_0.5Zn_0.5Fe₂O₄ nanopowders. The microstructure and magnetic property of the synthesized powders were comparatively studied. The results indicated that the synthesis technique and the template had remarkable dependence on the microstructure and the magnetic property of the nanopowders. The powder synthesized by the sol–gel method without any template had a maximum saturation magnetization of 73.6 emu g⁻¹ closing to the value of the bulk material (80 emu g⁻¹), while the PEG-4000 and CMC decreased the magnetization to 54.0 and 60.9 emu g⁻¹. The three powders showed almost same coercivity (314–343 Oe). However, the PEG-4000 and CMC in the hydrothermal process obviously decreased and increased the coercivity respectively from 1,464 Oe to 5 Oe and 4,304 Oe but had small effect of the magnetization (55.5–59.0 emu g⁻¹).     

Effect of V substitution on microstructure and ferroelectric properties of Bi<Subscript>3.6</Subscript>Ho<Subscript>0.4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films prepared by sol–gel method

Bi_3.6Ho_0.4Ti₃O₁₂ and (Bi_0.9Ho_0.1)_4−x/3Ti_3−x V _x O₁₂ (BHTV) (x = 0.3, 1.2, 3.0 and 6.0%) thin films were prepared on Pt/Ti/SiO₂/Si substrates by sol–gel method. The effect of V content on their microstructure and ferroelectric properties were investigated. All the BHTV samples consisted of the single phase of Bi-layered Aurivillius phase. The B-site substitution with high-valent cation of V⁵⁺, in Bi_3.6Ho_0.4Ti₃O₁₂ films, enhanced the remanent polarizations (2P_r) and reduced the coercive field (2E_c). The BHTV film with x = 0.3% exhibited the better electrical properties with 2P_r 45.5 μC/cm², 2E_c 257 kV/cm, good insulting behavior, as well as the fatigue-free characteristic.     

Hydrothermal process fabrication of NiO–NiCoO<Subscript>2</Subscript>–Co<Subscript>3</Subscript>O<Subscript>4</Subscript> composites used as supercapacitor materials

A composite consisting of Co₃O₄, NiCoO₂ and NiO is prepared by a simple and easy hydrothermal method followed by calcining at 300?°C. The composition, morphology and microstructure of NiO–NiCoO₂–Co₃O₄ composites are examined by X-ray diffraction, field emission scanning electron microscope and transmission electron microscopic. The electrochemical performances of NiO–NiCoO₂–Co₃O₄ composites are characterized by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy in 3 M KOH electrolyte. The results of electrochemical measurements show that the NiO–NiCoO₂–Co₃O₄ composites exhibit a high specific capacitance of 990 and 580 F/g at the current densities of 1.0 and 10 A/g, respectively. About 50% of the maximum specific capacitance can still be retained after 1000 continuous CD cycles at 10 A/g. It reveals a great potential of NiO–NiCoO₂–Co₃O₄ composites used in high-performance energy-storage systems.     

Crystallographic and magnetic properties of Fe-doped SnO<Subscript>2</Subscript> nanopowders obtained by a sol–gel method

We prepared Sn_1?x Fe _x O₂ (x = 0, 0.03, 0.05, 0.10, and 1.0) nanoparticles by the polymeric precursor method based on the modified Pechini process. Two types of starting reactants for both tin and iron were explored: Sn(II)/Fe(II) and Sn(IV)/Fe(III) precursors. Thermogravimetric analysis revealed that the precursor powders prepared from Sn(IV) have higher excess in ethylene glycol in comparison to precursor samples prepared from Sn(II). XRD patterns for those samples prepared from Sn(IV) and Fe(III) were adequately fitted by introducing only the cassiterite phase of SnO₂. Micro-Raman spectra also support these findings, and additionally it is found that the presence of iron broadened and reduced the intensities of the principal bands. ¹¹⁹Sn Mössbauer spectra indicated only the presence of Sn⁴⁺, whereas RT ⁵⁷Fe Mössbauer spectra suggested the presence of two Fe³⁺ sites located at different distorted sites. On the other hand, micro-Raman and ⁵⁷Mössbauer spectrometry showed the formation of hematite as impurity phase for those samples with iron concentrations above ~5 at.%, prepared from Fe(II) and Sn(II) precursors. In addition, their XRD patterns revealed larger average grain sizes for the cassiterite phase of SnO₂ in comparison to those samples prepared from Sn(IV) and Fe(III).     

Effect of sol–gel method on colour properties of the classical cobalt olivine (Co<Subscript>2</Subscript>SiO<Subscript>4</Subscript>) ceramic pigment

A sol–gel method based on (H ₂ S _{2 5}) _{a q} as silicon precursor in the presence of NaCl and KCl mineralizers was used for the synthesis of the classical cobalt olivine (Co ₂ SiO ₄ ) ceramic pigment. The effect of this synthesis route on the colour properties was studied. Highly pure olivine phase was obtained after firing at 1200 ^° C for 3 h. The resulting powders exhibited very intense violet colour, while their addition at only 1 wt% to an industrial transparent glaze was enough to produce a very intense blue–violet colouration. Based on the aspect of glazed ceramics, addition of pigments even at 0.5 wt% to the glaze resulted in a very interesting colour and opacity. By this appropriate minimization of the used pigment amount without compromising the colouring properties required during application, the obtained Co olivine could be more efficient, less toxic and less expensive.     

Thermoelectric properties of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9+δ</Subscript> with Lu substitution

A series of Ca_3−xLu_xCo₄O_9+δ (x = 0, 0.1, 0.2, and 0.4) has been prepared by sol–gel method. The effects of Lutetium substitution on thermoelectric properties of Ca₃Co₄O_9+δ have been systematically investigated from 4 to 335 K. With the partial substitution of Lu³⁺ for Ca²⁺, the resistivity and thermopower for Lu-doped samples increase, while their thermal conductivity decreases. The dimensionless figure of merit for Ca_2.8Lu_0.2Co₄O_9+δ material (ZT = 0.032) is about five times better than that for Ca₃Co₄O_9+δ (ZT = 0.007) at 335 K. Strikingly, for Lu-doped samples, the thermopower exhibits a steeper upturn at low temperatures.     

Microstructure,dielectric and photoluminescence properties of Tm-doped Ba<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>TiO<Subscript>3 </Subscript>thin films fabricated by sol–gel method

Ba_0.8Sr_0.2TiO₃ thin films doped by Tm from 0 to 7 mol% were fabricated by sol–gel method on silicon and Pt/Ti/SiO₂/Si substrates. X-ray diffraction, scanning electron microscopy, and Raman spectroscopy have been used to study variations of crystal structure, surface morphologies, and phase stability of Tm-doped BST films, respectively. The residual stress in BST films on silicon substrates can be reduced by Tm doping, as demonstrated by the blueshift of phonon peaks in Raman spectra. The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 1 kHz to 1 MHz. The grain size and dielectric constant decreased with increasing Tm concentration. While the variation of dielectric loss, tunability and the figure of merit were nonlinear with increasing Tm concentration. In addition, the photoluminescence property of 0.2 mol% Tm-doped BST was also studied. The effect of Tm doping on the microstructure, dielectric and photoluminescence properties were analyzed.     

MOF-derived carbon coating on self-supported ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript>–ZnO nanorod arrays as high-performance anode for lithium-ion batteries

The C–ZnCo₂O₄–ZnO nanorod arrays (NRAs), which consist of MOF-derived carbon coating on ZnCo₂O₄–ZnO NRAs, are rational designed and synthesized via a facile template-based solution route on Ti foil and used as high-performance anode for lithium-ion batteries (LIBs). The uniform coated MOF-derived carbon layers on the ZnCo₂O₄–ZnO nanorods surface can serve as a conductive substrate as well as buffer layer to restrain volume expansion during charge–discharge process. When tested as anodes for LIBs, the C–ZnCo₂O₄–ZnO NRAs show high reversible capacity of 1318 mA h g^?1 at 0.2 A g^?1 after 150 charge–discharge cycles. Furthermore, C–ZnCo₂O₄–ZnO NRAs also exhibit brilliant rate performance of 886.2, 812.8, 732.2 and 580.6 mA h g^?1 at 0.5, 1, 2 and 5 A g^?1, respectively. The outstanding lithium storage performance of C–ZnCo₂O₄–ZnO NRAs could be ascribed to the stimulated kinetics of ion diffusion and electron transport originated from the shortened lithium-ion diffusion pathway and improved electronic conductivity benefit from uniformly coating MOF-derived carbon.     

Synthesis of thorn-like Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>·H<Subscript>2</Subscript>O by hydrothermal method

Thorn-like polycrystalline Ca₂B₂O₅·H₂O microspheres with nano-sized slices were synthesized using boric acid and calcium hydroxide as reactants by a facile catalyst-free hydrothermal method at low temperature. The products were characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern reveals that the Ca₂B₂O₅·H₂O is a monoclinic phase polycrystalline with cell parameters a = 0·6702, b = 0·5419 and c = 0·3558 nm. SEM also reveals that the monoclinic phase polycrystalline are thorn-like microspheres composed of many flakes with an average thickness of <100 nm. Possible reaction and growth mechanism were also discussed.     

Photocatalytic degradation of diverse organic dyes by sol–gel synthesized Cd<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> nanostructures

Cd₂V₂O₇ nanostructures have been fabricated by Cd(NO₃)₂·4H₂O, NH₄VO₃ as precursor and diverse carboxylic acids as both fuel and capping agent via the simple and novel sol–gel route. Effect of carboxylic acid type and calcination temperature were studied to reach optimum condition. The Cd₂V₂O₇ nanostructures synthesized by citric acid as optimum size and morphology is composed of particles with the diameter in a range of 10–20 nm. The purity, crystalline phase, morphology, and optical properties were characterized by X-ray diffraction (XRD), Fourier transform IR (FT-IR), energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, and Photoluminescence. The photocatalytic property was performed using degradation of Erythrosine, Eriochrome Black T and Eosin Y aqueous solution under UV irradiation. The optimum removal efficiency is 77% in degradation of Eriochrome Black T.     

Effect of Zn<Superscript>2+</Superscript> doping on the structural,magnetic and dielectric properties of MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by the sol–gel method

Mn_1?xZn_xFe₂O₄ (x?=?0.2–0.8) ferrite samples were successfully prepared by the sol–gel method. X-ray diffraction study reveals that single cubic spinel phase was formed in Mn_1?xZn_xFe₂O₄ samples. The SEM micrographs revealed that the microstructures change significantly with different Zn²⁺ doping concentration and sintering temperature while the grain size grow up to 9.48 μm for Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C. Further, the dielectric and magnetic measurements indicated that both Zn²⁺ doping and sintering temperature could affect both electrical and magnetic parameters such as dielectric constant and saturation magnetization in a great manner. The Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C for 8 h is found to show the largest M _s value (77.30 emu/g) in this work. These results indicate that Zn²⁺ doping or sintering temperature can adjust the microstructures, dielectric and magnetic properties of Mn_1?xZn_xFe₂O₄ ferrites.     

Structure,dielectric property and impedance spectroscopy of La<Subscript>2/3</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics by sol–gel method

La_2/3Cu₃Ti₄O₁₂ (LCTO) precursor powders were synthesized by the sol–gel method. Effect of sol conditions and sintering process on microstructure and dielectric properties of LCTO powders or ceramics were investigated systematically. The optimum sol conditions for the synthesis of precursor powders were as follows: the Ti⁴⁺ concentration of 1.00 mol/L, the molar ratio of water and titanium of 5.6:1 and the sol pH of 1.0, respectively. After sintered at 1105 °C for 15 h, the LCTO ceramics exhibited more homogeneous microstructure, much higher dielectric constant (ca 09–1.6 × 10⁴) and lower dielectric loss (ca 0.057). The higher dielectric constant of the LCTO ceramics might be due to the internal barrier layer capacitor effect. The LCTO ceramics showed two kinds of conductivity activation energy for grain boundary conductivity from complex impedance analysis. The transition temperature of two activation energy values occured between 170 and 210 °C. The temperature range of 170–210 °C was critical pseudocritical region of the dielectric constant, dielectric loss and activation energy. Furthermore, it was concluded that the grain boundary play an important role for electrical properties.     

Very low loss tangent and giant dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics prepared by the sol–gel process

The pure phase of CaCu₃Ti₄O₁₂ (CCTO) powder can be successfully synthesized by the sol–gel process. CCTO ceramic samples were synthesized at different sintering temperatures of 1015 and 1050?°C and sintering times of 8 and 10 h. X-ray diffraction results indicated a pure phase for all ceramic samples. Rietveld refinements were adopted for the calculation of lattice constants. Scanning electron microscopy micrographs revealed the effect of sintering conditions on the microstructural evolution of ceramic samples. X-ray absorption near edge spectroscopy was performed to determine the oxidation state of Cu and Ti ions in ceramic samples. The dielectric and non-linear current voltage properties of CCTO ceramic samples were systematically investigated. Interestingly, very low loss tangent (tanδ?<?0.017 at 30?°C and 1 kHz) and giant dielectric constant (ε′?～?10,942) with temperature coefficients less than ±15% in a wide temperature range of ?60 to 125?°C were obtained in the CCTO ceramic sample sintered at 1015?°C for 10 h (CCTO1-10). This suggests a potential use for CCTO1-10 sample in capacitor applications. All CCTO ceramic samples display non-linear characteristic with non-linear coefficient (α) and breakdown field (E _b ) values in the range of 5.69–11.02 and 1415–4294, respectively.