Structure and piezoelectric properties of new ternary K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–LiSbO<Subscript>3</Subscript>–CaTiO<Subscript>3</Subscript> lead-free piezoceramics

New ternary (1−x)K_0.5Na_0.5NbO₃–x(0.80LiSbO₃–0.20CaTiO₃) lead-free ceramics were fabricated by a conventional ceramic technique and their structure and piezoelectric properties were studied. The results of X-ray diffraction reveal that LiSbO₃ and CaTiO₃ diffuse into the K_0.5Na_0.5NbO₃ lattices to form a new solid solution with a perovskite structure. After the addition of LiSbO₃ and CaTiO₃, the cubic-tetragonal and tetragonal-orthorhombic phase transitions shift to lower temperatures. Coexistence of the orthorhombic and tetragonal phases is hence formed in the ceramics with 0.03 < x < 0.07 at room temperature, leading to a significant enhancement of the piezoelectric properties. For the ceramics with x = 0.04–0.06, the piezoelectric properties become optimum: d ₃₃ = 172–253 pC/N, k _P = 49.9–55.5%, k _t = 49.2–52.1% and T _C = 348–373 °C. The ceramic with x = 0.04 also exhibits a good thermal stability of piezoelectric properties.     

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).     

Good thermal stability and improved piezoelectric properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript>–Bi(Mg<Subscript>0.75</Subscript>W<Subscript>0.25</Subscript>)O<Subscript>3</Subscript> solid solutions

In this paper, (1 ? x)(K_0.5Na_0.5)NbO₃–xBi(Mg_0.75W_0.25)O₃ (x = 0–0.015) lead-free dielectric ceramics were investigated. XRD analysis certified that the Bi(Mg_0.75W_0.25)O₃ has diffused into (K_0.5Na_0.5)NbO₃ to fabricate a new solid solution. The addition of Bi(Mg_0.75W_0.25)O₃ depressed the orthorhombic–tetragonal phase transition temperature from 210 to 176 °C and tetragonal–pseudocubic phase transition temperature (Curie point) from 419 to 400 °C. As x = 0.005, the ceramics exhibited high relative permittivity (ε ~ 1325), low dielectric loss (tan δ < 2.9%) tan δ stability (Δε/ε_168°C ≤ ±15%) in the temperature range of 168 ~ 369 °C. Especially, the ceramics also showed optimized piezoelectric constant (d ₃₃ = 122 pC N^?1) and remnant polarization (P_r = 32.57 μC cm^–2). These results indicated that the BMW added ceramics have potential applications in ferroelectric and thermal stability devices.     

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 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.     

Study of structural and magnetoelectric properties of 1−x(Ba<Subscript>0.96</Subscript>Ca<Subscript>0.04</Subscript>TiO<Subscript>3</Subscript>)–x(ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>) ceramic composites

Multiferroic ceramic composites of (1?x)Ba_0.96Ca_0.04TiO₃–(x)ZnFe₂O₄ (BCT-ZF) were prepared from ferroelectric (FE) barium calcium titanate (BCT) and ferromagnetic (FM) zinc ferrite (ZF) by using the solid state reaction method with different mol% fractions of x (x?=?0.1 and 0.2). The preliminary structural studies carried out by X-ray diffraction at room temperature reveals that the samples have a tetragonal structure along with the cubic spinel ferrite phase. Raman spectra of the composites also confirm the existence of BCT phase and ZF phase. The room temperature ferroelectric polarization measurements as a function of magnetic field show the existence strong magnetoelectric coupling of 10.85 (mV/(cm.Oe).     

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.     

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.     

Enhanced dielectric and piezoelectric properties of (100) oriented Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–SrTiO<Subscript>3</Subscript> thin films

The (100) oriented and random oriented 0.755Bi_0.5Na_0.5TiO₃–0.065BaTiO₃–0.18SrTiO₃ (BNT–BT–ST) thin films were deposited on LaNiO₃ (LNO) buffered Pt(111)/Ti/SiO₂/Si substrates by the sol–gel processing technique. The orientation is controlled by the concentration of solution. The structure, dielectric and piezoelectric properties of the thin films are significantly affected by the crystallographic orientation. The (100) oriented BNT–BT–ST thin film has improved dielectric and piezoelectric properties. For the (100) oriented and random oriented BNT–BT–ST thin films, the dielectric constants are 660 and 550, the dielectric losses are 0.045 and 0.076 and the effective piezoelectric coefficients are 140 and 110 pm/V, respectively. The large piezoelectric response is attributed to the uniform microstructure and increased lattice distortion along (100) direction.     

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.     

Microstructure and electrical properties of (Na<Subscript>1.015−x</Subscript>K<Subscript>x</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

In order to obtain the morphotropic phase boundary (MPB) and good piezoelectric properties, lead-free (Na_1.015−xK_x)NbO₃ (x = 0.32–0.35) piezoceramics were synthesized by conventional solid state sintering. The x-ray diffraction results show that the lattice parameters of the monoclinic primitive cell peak at x = 0.34. The scanning electron microscopy and energy dispersive spectroscopy reveal that the excess sodium may be an important reason for the abnormal growth of the grains larger than 20 μm. All the samples exhibit double-like hysteresis loops and it may also be attributed to the excess Na⁺. Although the salient microstructure was found in the studied range, the piezoelectric and ferroelectric properties changed slightly with increasing x from 0.32 to 0.35. The values of piezoelectric coefficient d ₃₃ obtained in this study are as high as about 75 pC/N which is close to that of normally prepared (Na_0.5K_0.5)NbO₃ ceramics with MPB structure.     

Dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xBaNb₂O₆ (BNT–BN100x), a new member of the BNT-based group, was prepared by conventional solid state reaction. X-ray diffraction showed that BaNb₂O₆ (BN) diffused into the lattice of Bi_0.5Na_0.5TiO₃ to form a solid solution with perovskite-type structure. The temperature dependence of dielectric constant ε_r revealed that the solid solution underwent two phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. Both the transition temperature T _d and T _m were shifted to lower with the increasing content of BaNb₂O₆. The temperature dependence of dielectric constant at different frequency revealed that the solid solution exhibited obviously dielectric relaxation characteristics. The sample with x = 0.6 mol% exhibited excellent electrical properties, piezoelectric constant d ₃₃ = 94 pC/N; electromechanical coupling factor k _p = 0.185. The results showed that BNT–BN100x ceramics were good candidates for use as lead-free piezoelectric ceramics.     

Phase formation and dielectric properties of ceramics in the BiFeO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–Bi(Mg<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> system

We have studied the effect of Bi(Mg_0.5Ti_0.5)O₃ additions on the phase formation, structural parameters, microstructure, and dielectric properties of solid solutions in the region of a morphotropic phase boundary in the BiFeO₃–BaTiO₃ system. Single-phase samples with the perovskite structure have been obtained and the addition of Bi(Mg_0.5Ti_0.5)O₃ has been shown to raise the Curie temperature of the ceramics and improve their dielectric properties.     

Thermal and dielectric properties of the LTCC composites based on the eutectic system BaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The low-temperature co-fired ceramic (LTCC) composites containing quartz based on the eutectic system BaO–Al₂O₃–SiO₂–B₂O₃ are fabricated at the sintering temperature below 980 °C. Preparation process and sintering mechanism were described and discussed, respectively. The results indicated that the addition of quartz to the eutectic system can availably improve dielectric properties of the LTCC composites. In addition, The LTCC composites with optimum compositions, which were obtained by the regulation of an Al₂O₃ content in the composite, can express excellent dielectric properties (permittivity: 5.94, 5.48; loss: 7 × 10⁻⁴, 5 × 10⁻⁴), considerable CTE values (11.7 ppm. °C⁻¹, 10.6 ppm. °C⁻¹) and good mechanical properties (128 MPa,133 MPa).     

Ferroelectric and piezoelectric properties of new NaNbO<Subscript>3</Subscript>–Bi<Subscript>0.5</Subscript>K<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> lead-free ceramics

New lead-free ceramics (1–x)NaNbO₃–xBi_0.5K_0.5TiO₃ have been fabricated by the conventional ceramic sintering technique, and their ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction reveal that Bi_0.5K_0.5TiO₃ diffuses into the NaNbO₃ lattices to form a new perovskite-type solid solution with orthorhombic symmetry. The addition of a small amount of Bi_0.5K_0.5TiO₃ (x ≥ 0.025) transforms the ceramics from antiferroelectric to ferroelectric. The ceramic with x = 0.10 possesses the largest remanent polarization P _r and thus exhibits the optimum piezoelectric properties, giving d ₃₃ = 71 pC/N, k _p = 16.6% and k _t = 39.7%. The ceramics with low doping level of Bi_0.5K_0.5TiO₃ are normal ferroelectrics and the ferroelectric-paraelectric phase transition becomes diffusive gradually with the doping level x of Bi_0.5K_0.5TiO₃ increasing. Our results show the (1–x)NaNbO₃–xBi_0.5K_0.5TiO₃ ceramics is one of the good candidates for lead-free piezoelectric and ferroelectric materials.     

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.     

Crystal structure and properties of BaTiO<Subscript>3</Subscript>–(Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript> ceramic system

(1 − x)BaTiO₃–x(Bi_0.5Na_0.5)TiO₃ (x ranged from 0.01 to 0.96) ceramics were fabricated by the conventional ceramic technique. The crystal structure, as well as dielectric and piezoelectric properties of the ceramics were studied. All the ceramics formed single-phase solid solutions with perovskite structure after sintering in air at 1150–1250 °C for 2–4 h. The crystal structure and microstructure varied gradually with the increase of (Bi_0.5Na_0.5)TiO₃ (BNT) content. The Curie temperature, T _c, shifted monotonously to high temperature as BNT increased. The ceramics with 20–90 mol% BNT had relatively low and stable dielectric loss characteristics. The piezoelectric constant, d ₃₃, enhanced with the increase of BNT content through a maximum value in a composition of 93 mol% BNT and then tended to decrease. The maximum value, 148 pC/N, of piezoelectric constant d ₃₃ together with the electromechanical coupling factors, k _t, 19.8% and k _p, 15.8%, were obtained when BNT was 93 mol%.     

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.     

Thermodynamic and structural properties of PrBaCo<Subscript>2</Subscript>O<Subscript>5 + δ</Subscript>

The oxygen content of the double cobaltite PrBaCo₂O_{5 + δ} was determined by coulometric titration in broad temperature and oxygen pressure ranges, and the partial thermodynamic functions of oxygen were evaluated. The results on the nonstoichiometry and structural properties of PrBaCo₂O_{5 + δ} demonstrate that, at 5 + δ < 5.3, this cobaltite has a high-temperature phase with lattice parameters a = 11.774 Å, b = 11.932 Å, and c = 7.609 Å. The composition dependences of \(\Delta \bar H(O)\) and \(\Delta \bar S(O)\) indicate that the 3a_p × 3a_p × 2a_p orthorhombic structure persists in the range 5.15 ≤ 5 + δ ≤ 5.30. Some of the Co³⁺ ions are shown to disproportionate according to the scheme 2Co³⁺=Co²⁺+Co⁴⁺.     

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.