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).     

Rational synthesis and tailored optical and magnetic characteristics of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Au composite nanoparticles

To minimize saturation magnetization (Ms) degradation and simultaneously maintain the optical and magnetic responsiveness characteristics of Fe₃O₄/Au nanocomposites, we successfully prepared Fe₃O₄–Au seeds composite nanoparticles (NPs) by a novel seed deposition process. The effects of gold seeds coating amounts and the concentration of Fe₃O₄ NPs on the morphologies of final products are extensively characterized. The results of energy-dispersive spectrometry mapping show that the gold seeds are uniformly adhered onto the Fe₃O₄ NPs surfaces in precisely controlled amount. Importantly, with the electronic redistribution between Fe₃O₄ and Au NPs interfaces, the obvious position shifting of Fe 2p and Au 4f electronic binding energy peaks is observed. Upon increasing surface coatings of gold seeds, the electron deficiency on the gold NPs leads to the redshift of the absorption peak. Though Ms declines slightly due to the diamagnetic contribution from decorated gold seeds, the developed Fe₃O₄–Au seeds composite NPs possess the robust magnetic responsiveness and they are amenable to be separated and recycled by the external magnet, which facilitates great potential applications in biological, medical and photocatalytic fields.     

Enhanced antibacterial performance of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Ag and MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>–Ag nanocomposites

In this work, we have described the antibacterial activities of Fe₃O₄ nanoparticles with different organic parts, including Humic acid (HA), Nicotinic acid (Nico) and Histidine (His), and the antibacterial activity of MnFe₂O₄ nanoparticles coated with PANI and SiO₂ against different bacteria and some standard antibacterial drugs. The present study revealed that the newly fabricated various Fe₃O₄ and MnFe₂O₄ nanocomposites, when combined with some different organic parts, are superiour antibacterial agents. Also, the synthesized nanocomposites can be easily separated from aqueous solution by magnetic filtration without any contamination of the medium.     

Comparative study of multilayered ZnO/TiO<Subscript>2</Subscript>/ZnO and TiO<Subscript>2</Subscript>/ZnO/TiO<Subscript>2</Subscript> thin films prepared by sol–gel dip coating method

The aim of this research work is to represent the comparative study of ZnO/TiO₂/ZnO (ZTZ) and TiO₂/ZnO/TiO₂ (TZT) thin films deposited by sol–gel dip coating on FTO substrates. After deposition, the films were annealed at 500 °C for 1 h. Structural, surface morphology, optical and electrical properties of these films were studied by X-ray diffractrometer (XRD), Raman spectra, atomic force microscope (AFM), photoluminescence spectra (PL) and four point probe technique respectively. XRD and Raman spectra confirmed the anatase, brookite phases of TiO₂ and cubic phase of ZnO. AFM confirmed the formation of nano particles with average sizes of 18.4 and 47.2 nm of TZT and ZTZ films respectively. According to PL spectra, both the multilayer films slowdown the electron hole recombination rate and enhances the optoelectronic properties of the materials. Also it showed the peaks in the visible region of spectrum. The four point probe results showed that the average sheet resistivity of the films is 450 and 120 (ohm-m) respectively.     

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.     

Nanostructured Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> composite synthesized by sol–gel technique: powder processing and microstructure

Al₂O₃–ZrO₂ composite gel powder was prepared by sol–gel route. The gel precursor compositions were preferred to achieve yield of 5–15 mol% zirconia after calcination of respective powders. The precursor gel was characterized by Differential Thermal Analysis (DTA)/Thermo Gravimetric (TG), IR and X-ray Diffraction study (XRD). The analysis reveal the gel contained pseudoboehmite and amorphous Zr(OH)₄, which was decomposed in three and two stages respectively. The phase transformation of alumina during calcination followed the sequence of pseudoboehmite → bayerite → boehmite → γ-Al₂O₃ → θ-Al₂O₃ → α-Al₂O₃, while that of ZrO₂ follows amorphous ZrO₂ → t-ZrO₂ → (t + m) ZrO₂. Fourier Transform Infrared Spectroscopy (FTIR) studies showed that the number of M–OH and M–O bond increases with zirconia due to a change in the cationic charge of the composite powder. Transmission Electron Microscopy (TEM) photograph of calcined powder exhibited the presence of dispersed as well as agglomerated nano sized spherical particles. SEM and Electron Probe Microscope Analysis (EPMA) confirmed the near uniform distribution of zirconia particles in the alumina matrix.     

Synthesis and microwave absorption enhancement of yolk–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@C microspheres

Rational design on the microstructure of microwave-absorbing materials is paving the way for upgrading their performances in electromagnetic pollution prevention. In this study, a Fe₃O₄/C composite with unique yolk–shell microstructure (YS-Fe₃O₄@C) is successfully fabricated by a silica-assisted route. It is found that carbon shells in this composite can make up the shortages of Fe₃O₄ microspheres in dielectric loss ability, while they may more or less attenuate the intrinsically magnetic loss of Fe₃O₄ microspheres. The microwave absorption properties of YS-Fe₃O₄@C are evaluated in the frequency range of 2.0–18.0 GHz in terms of the measured complex permittivity and complex permeability. The results demonstrate that YS-Fe₃O₄@C can exhibit much better performance than bare Fe₃O₄ microspheres and individual carbon materials, as well as core–shell Fe₃O₄/C composite (CS-Fe₃O₄@C), where strong reflection loss and wide response bandwidth can be achieved simultaneously. With an absorber thickness of 2.0 mm, the maximum reflection loss is ?73.1 dB at 14.6 GHz and a bandwidth over ?10.0 dB is in the range of 12.3–18.0 GHz. It can be proved that the unique yolk–shell microstructure is helpful to reinforce the dielectric loss ability and create an optimized matching of characteristic impedance in the composite.     

Structure of SrCo<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>O<Subscript>3 − δ</Subscript>-based composites prepared by sol-gel and mechanochemical processes

X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy have been used to investigate the structural phase transformations of SrCo_0.5Fe_0.5O_{3 ? δ}-based mixed-oxide nanocomposites containing fine iron oxide particles. The nanocomposites have been prepared using sol-gel and mechanochemical processes. The addition of iron(III) oxide sol to SrCo_0.5Fe_0.5O_{3 ? δ} xerogel is shown to enhance the thermal stability of the resultant cubic perovskite phase. The stabilization is due to partial shielding of the perovskite surface with a thin Fe₂O₃ layer, which hinders cobalt diffusion to the surface, preventing Co₃O₄ formation.     

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.     

Crystallization and microstructural evolution of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–La<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-ceramics

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2Al₂O₃·2.8SiO₂·1.2TiO₂·xLa₂O₃ (x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different La₂O₃ concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the “regions” (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the “regions” is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of La₂O₃, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

Compositional dependence of the structural and dielectric properties of Li<Subscript>2</Subscript>O–GeO<Subscript>2</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

(10Li₂O–20GeO₂–30ZnO–(40-x)Bi₂O₃–xFe₂O₃ where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant ε′, loss tan δ, AC conductivity, σ _ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T _g and onset of crystallization temperature T _x increase with the variation of concentration of Fe₂O₃ referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe₂O₃ content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO₃, BiO₆, ZnO₄, GeO₄, and GeO₆. The structural changes observed by varying the Fe₂O₃ content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi₂O₃, GeO₂, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe₂O₃ content.     

Synthesis and photocatalytic behaviors of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>–CNT/TiO<Subscript>2</Subscript> composite materials under visible light

Cr₂O₃–CNT/TiO₂ composites derived from chromium acetylacetonate, multi-walled carbon nanotubes (MWCNT) and titanium n-butoxide (TNB) were prepared, and the photocatalytic activity of the Cr₂O₃–CNT and CNT/TiO₂ composites was examined. The Cr₂O₃–CNT/TiO₂ composites were characterized by BET surface area measurement, X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray analysis. The photocatalytic activity was determined from the decomposition of methylene blue (MB) under visible light irradiation. Methylene blue was photodegraded successfully in the presence of the Cr₂O₃–CNT/TiO₂ composite under visible light irradiation.     

Preparation,structure and microwave dielectric properties of 3MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–3TiO<Subscript>2</Subscript> ceramics

3MgO–Al₂O₃–3TiO₂ (MAT) ceramics were prepared by a conventional solid-state reaction method. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and network analyzer. MAT ceramics contained the coexistence of three phases, including MgAl₂O₄, MgTiO₃ and MgTi₂O₅. The ceramics sintered at 1350 °C for 4 h presented excellent comprehensive performances with relative permittivity (ε _r ) of 15.4, quality factor (Q × f) of 91,000 GHz and temperature coefficient of resonant frequency (τ _f ) about ?55.1 ppm/°C.     

Preparation and microwave absorbing performance of TiO<Subscript>2</Subscript>/ NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> /hollow glass microsphere composite with core–shell structure

Microwave absorbing TiO₂/NiFe₂O₄/HGM composite with core–shell structure was prepared via a facile two-step method. The obtained composite was then investigated by SEM, TEM, XRD, XPS, VSM and a vector network analyzer. The results indicated that HGM was completely coated by NiFe₂O₄ nanospheres after the hydrothermal reaction, and TiO₂/NiFe₂O₄/ HGM composite with core–shell structure was also successfully synthesized. The composite exhibited excellent magnetic performance and microwave absorption capacity. Measurement of VSM suggested that the saturated magnetization values (Ms) of TiO₂/NiFe₂O₄/HGM was 27.79 emu.g^??1. When the frequency was 10.3 GHz, the R _L value of TiO₂/NiFe₂O₄/HGM composite with the thickness of 2.6 mm could reach up to ?20 dB. The obtained composite exhibited excellent microwave absorbing properties, which could be used as a promising EM wave absorber.     

The effect of Fe contents on the local structure and crystallization behavior of SiO<Subscript>2</Subscript>–CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The glass and glass ceramics containing SiO₂–CaO–Fe₂O₃–P₂O₅ were prepared by sol–gel method. The influence of the Fe contents on the crystallization and local structure of the glass and glass ceramics was systematically investigated. The crystal structure of the glass ceramics was identified by XRD characterization. Hematite phase can be precipitated from the glass matrix in all glass ceramics with various Fe contents, and the crystallographic parameters of hematite were determined by XRD Rietveld refinement. The crystallization kinetics of the glasses was investigated in detail. Relative low activation energies were obtained at low Fe contents. The local structure evolution of the glass and glass ceramics has been studied in-depth by means of FTIR and Mössbauer spectroscopy. Fe element is present both as network former and network modifier which significantly influenced the crystallization activation energies of the glasses. The results of this work may be of great significance for the material design and practical applications of bioactive magnetic glass ceramics for hyperthermia.     

Enhanced microwave dielectric properties of Ba<Subscript>0.40</Subscript>Sr<Subscript>0.60</Subscript>TiO<Subscript>3</Subscript>–Zr<Subscript>0.80</Subscript>Sn<Subscript>0.20</Subscript>TiO<Subscript>4</Subscript> composite ceramics

The (1−x) Ba_0.40Sr_0.60TiO₃ (BST)−xZr_0.80Sn_0.20TiO₄ (ZST) composite ceramics with x = 10, 20, 30, and 40 wt% were fabricated by conventional solid-state reaction method. With increasing of ZST content, the dielectric constant of composite ceramics was decreased and dielectric loss increases. The effect of ZnO addition to 70 wt% BST–30 wt% ZST composition on the microstructure and dielectric properties was investigated. The improvements in dielectric constant, dielectric loss, and microwave dielectric properties of composite ceramics can be achieved by ZnO addition. The sample with 98 wt% (70 wt% BST–30 wt% ZST)–2 wt%ZnO composition exhibits promising dielectric properties, with dielectric constant, loss tangent and tunability at 4 kV/mm, of 125, 0.0016 and 12%, at 10 kHz and room temperature. At ~2 GHz, it possesses a dielectric constant of 101 and a Q factor of 187, which makes it a good candidate for tunable microwave device applications.     

Phase formation and dielectric properties of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> by slow injection sol–gel technique

A simple sol–gel process incorporating slow precursor injection technique was employed to synthesize homogeneous Ba_0.5Sr_0.5TiO₃ nano powders. The Ba_0.5Sr_0.5TiO₃ samples were subjected to calcination temperatures from 600 to 1,100 °C and sintering temperatures from 1,250 to 1,350 °C for the study of phase formation, crystallite size, particle distribution, and dielectric properties. Single phase Ba_0.5Sr_0.5TiO₃ with a cubic perovskite structure was successfully synthesized after calcination at 800 °C. The average size of the nano particles is 42 nm with a narrow size distribution, and a standard deviation of 10%. The highest values recorded within the investigated range for dielectric constant, and dielectric loss measured at 1 kHz are 1,164 and 0.063, respectively, for Ba_0.5Sr_0.5TiO₃ pellets calcined at 800 °C and sintered at 1,350 °C. Leakage current density measured at 5 V for the Ba_0.5Sr_0.5TiO₃ pellet was found to be 49.4 pA/cm².     

Evaluation of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Na<Subscript>2</Subscript>O–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> bioglass-ceramics for hyperthermia application

Magnetic bioglass ceramics (MBC) are being considered for use as thermoseeds in hyperthermia treatment of cancer. While the bioactivity in MBCs is attributed to the formation of the bone minerals such as crystalline apatite, wollastonite, etc. in a physiological environment, the magnetic property arises from the magnetite [Fe₃O₄] present in these implant materials. A new set of bioglasses with compositions 41CaO · (52 ? x)SiO₂ · 4P₂O₅  · xFe₂O₃ · 3Na₂O (2 ≤ x ≤ 10 mol% Fe₂O₃) have been prepared by melt quenching method. The as-quenched glasses were then heat treated at 1050°C for 3 h to obtain the glass-ceramics. The structure and microstructure of the samples were characterized using X-ray diffraction and microscopy techniques. X-ray diffraction data revealed the presence of magnetite in the heat treated samples with x ≥ 2 mol% Fe₂O₃. Room temperature magnetic property of the heat treated samples was investigated using a Vibrating Sample Magnetometer. Field scans up to 20 kOe revealed that the glass ceramic samples had a high saturation magnetization and low coercivity. Room temperature hysteresis cycles were also recorded at 500 Oe to ascertain the magnetic properties at clinically amenable field strengths. The area under the magnetic hysteresis loop is a measure of the heat generated by the MBC. The coercivity of the samples is another important factor for hyperthermia applications. The area under the loop increases with an increase in Fe₂O₃ molar concentration and the. coercivity decreases with an increase in Fe₂O₃ molar concentration The evolution of magnetic properties in these MBCs as a function of Fe₂O₃ molar concentration is discussed and correlated with the amount of magnetite present in them.