Crystalline phases and magnetic properties of Cu-Bi-Zn co-doped Co2Z ferrites

The effects of Cu, Bi and Zn substitutions on the crystalline phase and magnetic properties of hexagonal ferrites with a composition of 3(Ba_1−xBi_xO)2(Co_1−yCu_yO)12(Fe_2-(x/4)Zn_(x/4)O₃) were investigated. The results showed that the addition of Bi and Zn can significantly promote Z phase formation. The Z phase may be triggered to decompose into U and W phases resulting from the evaporation of Bi and segregation of Co-rich ferrites at high sintering temperatures for samples with large amounts of Bi and Zn. The initial permeability decreased with increasing x value because the Bi substitution promoted Z phase decomposition into U and W phases.     

Microwave dielectric properties of temperature stable Li2ZnxCo1−xTi3O8 ceramics

The Li₂Zn_xCo_1−xTi₃O₈ (x = 0.2-0.8) solid solution system has been synthesized by the conventional solid-state ceramic route and the effect of Zn substitution for Co on microwave dielectric properties of Li₂CoTi₃O₈ ceramics has also been investigated. The microwave dielectric properties of these ceramics show a linear variation between the end members for all compositions. The optimized sintering temperatures of Li₂Zn_xCo_1−xTi₃O₈ ceramics increase with increasing content of Zn. The specimen with x = 0.4 sintered at 1050 °C/2 h exhibits an excellent combination of microwave dielectric properties with ?_r = 27.7, Q_u × f = 57,100 GHz and τ_f = −1.0 ppm/°C.     

Power factor enhancement in Zn-doped Na0.8CoO2

The thermoelectric properties of Na_0.8Zn_xCo_1−xO₂/(ZnO)_y (x ≤ 0.01, 0 ≤ y ≤ 0.14) have been systematically investigated. The results suggest that doping divalent Zn ions within solubility limit x^* ∼ 0.01 leads to simultaneous reduction in resistivity and enhancement of thermopower. Analysis of the results show that the reduction of resistivity may be attributed to improved mobility of carriers, while the enhancement of thermopower may originate from the geometric relaxation of distorted CoO₆ octahedra caused by partial Zn substitution, leading to a narrower band width in the strongly correlated environment, consequently resulting in a remarkable 20% improvement in power factor.     

Low temperature sintering and microwave dielectric properties of (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics with BaCu(B2O5) additions

The effects of BaCu(B₂O₅) additives on the sintering temperature and microwave dielectric properties of (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics were investigated. The (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics were not able to be sintered below 1000 °C. However, when BaCu(B₂O₅) were added, they were sintered below 1000 °C and had the good microwave dielectric properties. It was suggested that a liquid phase with the composition of BaCu(B₂O₅) was formed during the sintering and assisted the densification of the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics at low temperature. BaCu(B₂O₅) powders were produced and used to reduce the sintering temperature of the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics. Good microwave dielectric properties of Q × f = 35,000 GHz, ?_r = 18.5.0 and τ_f = −51 ppm/°C were obtained for the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics containing 7 wt.% mol% BaCu(B₂O₅) sintered at 950 °C for 4 h.     

High sintering resistance of a novel thermal barrier coating

Sintering resistance of a novel thermal barrier coating Nd_xZr_1 − xO_y with Z dissolved in, where 0 < x < 0.5, 1.75 < y < 2 and Z is an oxide of a metal selected from Y, Mg, Ca, Hf and mixtures thereof, was studied. The coatings of Nd_xZr_1 − xO_y and typical 7YSZ were deposited by electron beam physical vapor deposition (EB-PVD) and air plasma spray (APS). The samples with the coating system of EB-PVD Nd_xZr_1 − xO_y or 7YSZ overlaid onto a MCrAlY bond coat were cyclically sintered at 1107 °C for 706 hours. The freestanding coatings of EB-PVD Nd_xZr_1 − xO_y and 7YSZ were isothermally sintered at 1371 °C for 500 hours. The microstructure of EB-PVD Nd_xZr_1 − xO_y before and after the sintering was evaluated and compared with EB-PVD 7YSZ. The sintering resistance of freestanding APS Nd_xZr_1 − xO_y coating was also investigated after isothermal sintering at 1200 °C for 50 and 100 hours. The results demonstrated that the new coatings of Nd_xZr_1 − xO_y applied with both EB-PVD and APS have higher sintering resistance than EB-PVD and APS 7YSZ, respectively.     

Microwave dielectric properties of (1 − x)ZnMoO4-xTiO2 composite ceramics

(1 − x)ZnMoO₄-xTiO₂ (x = 0.0, 0.05, 0.158, 0.25, and 0.35) composite ceramics were synthesized by the conventional solid state reaction process. The sintering behavior, phase composition, chemical compatibility with silver, and microwave dielectric properties were investigated. All the specimens can be well densified below 950 °C. From the X-ray diffraction analysis, it indicates that the triclinic wolframite ZnMoO₄ phase coexists with the tetragonal rutile TiO₂ phase, and it is easy for silver to react with ZnMoO₄ to form Ag₂Zn₂(MoO₄)₃ phase and hard to react with TiO₂. When the volume fraction of TiO₂ (x value) increasing from 0 to 0.35, the microwave dielectric permittivity of the (1 − x)ZnMoO₄-xTiO₂ composite ceramics increases from 8.0 to 25.2, the Q_f value changes in the range of 32,300-43,300 GHz, and the temperature coefficient τ_f value varies from −128.9 to 157.4 ppm/°C. At x = 0.158, the mixture exhibits good microwave dielectric properties with a ?_r = 13.9, a Q_f = 40,400 GHz, and a τ_f = +2.0 ppm/°C.     

Structural, elastic and electronic properties of Mg(Cu1−xZnx)2 alloys calculated by first-principles

The structural, elastic and electronic properties of Mg(Cu_1−xZn_x)₂ alloys (x = 0, 0.25, 0.5,and 0.75) were investigated by means of first-principle calculations within the framework of density functional theory (DFT). The calculation results demonstrated that the partial substitution of Cu with Zn in MgCu₂ leaded to an increase of lattice constants, and the optimized structural parameters were in very good agreement with the available experimental values. From energetic point of view, it was found that with increase of Zn content the structural stability of Mg(Cu_1−xZn_x)₂ alloys decreased apparently. The single-crystal elastic constants were obtained by computing total energy as a function of strain, and then the bulk modulus B, shear modulus G, Young's modulus Y and Poisson's ratio ν of polycrystalline aggregates were derived. The calculated results showed that among the Mg(Cu_1−xZn_x)₂ alloys, MgCuZn exhibited the largest stiffness, while Mg₂Cu₃Zn showed the best ductility. Finally, the electronic density of states (DOSs) and charge density distribution were further studied and discussed.     

Effects of Tl-filling into the voids and Rh substitution for Co on the thermoelectric properties of CoSb3

In order to enhance the thermoelectric (TE) properties of CoSb₃, we tried to reduce the lattice thermal conductivity (κ_lat) by filling Tl into the voids and substitution of Rh for Co. We prepared polycrystalline samples of Tl_x(Co_1−yRh_y)₄Sb₁₂ (x = 0, 0.05, 0.10, 0.15, 0.20 and y = 0.1, 0.2) and examined their TE properties from room temperature to 750 K. All the samples indicated negative values of the Seebeck coefficient (S). Both the electrical resistivity and the absolute values of the S decreased with increasing the Tl-filling ratio. The Tl-filling and Rh substitution reduced the κ_lat, due to the rattling and the alloy scattering effects. The minimum value of the κ_lat was 1.54 W m⁻¹ K⁻¹ at 550 K obtained for Tl_0.20(Co_0.8Rh_0.2)₄Sb₁₂. Tl_0.20(Co_0.8Rh_0.2)₄Sb₁₂ exhibited the best TE performance; the maximum value for the dimensionless figure of merit ZT was 0.58 at around 600 K.     

Synthesis and characterization of MWCNTs/Co1−xZnxFe2O4 magnetic nanocomposites and their use in hydrogels

A novel magnetic nanocomposite of multiwalled carbon nanotubes (MWCNTs) decorated with Co_1−xZn_xFe₂O₄ nanocrystals was synthesized successfully by an effective solvothermal method. The as-prepared MWCNTs/Co_1−xZn_xFe₂O₄ magnetic nanocomposite was used for the functionalization of P/H hydrogels as a prototype of device to show the potential application of the nanocomposites. The nanocomposites were characterized by X-ray diffraction analysis, transmission electron microscopy and vibrating sample magnetometer. The results show that the saturation magnetization of the MWCNTs/Co_1−xZn_xFe₂O₄ magnetic nanocomposites increases with x when the Zn²⁺ content is less than 0.5, but decreases rapidly when the Zn²⁺ content is more than 0.5. The saturation magnetization as a function of Zn²⁺ substitution reaches a maximum value of 57.5 emu g⁻¹ for x = 0.5. The probable synthesis mechanism of these nanocomposites was described based on the experimental results.     

A new temperature stable microwave dielectric ceramics: ZnTiNb2O8 sintered at low temperatures

The phases, microstructure and microwave dielectric properties of ZnTiNb₂O₈-xTiO₂ composite ceramics with different weight percentages of BaCu(B₂O₅) additive prepared by solid-state reaction method have been investigated using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results showed that the microwave dielectric properties were strongly dependent on densification, grain sizes and crystalline phases. The sintering temperature of ZnTiNb₂O₈ ceramics was reduced from 1250 °C to 950 °C by doping BaCu(B₂O₅) additive and the temperature coefficient of resonant frequency (τ_f) was adjusted from negative value of −52 ppm/°C to 0 ppm/°C by incorporating TiO₂. Addition of 2 wt% BaCu(B₂O₅) in ZnTiNb₂O₈-xTiO₂ (x = 0.8) ceramics sintered at 950 °C showed excellent dielectric properties of ?_r = 38.89, Q × f = 14,500 GHz (f = 4.715 GHz) and τ_f = 0 ppm/°C, which represented very promising candidates as LTCC dielectrics for LTCC applications.     

Chemical synthesis, structural and magnetic properties of nano-structured Co-Zn-Fe-Cr ferrite

Nanoparticles of Co_1−xZn_xFe_2−xCr_xO₄ (x = 0.0-0.5) ferrites were prepared by chemical co-precipitation technique using metal sulphates. The structural and magnetic properties were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and AC susceptibility measurements. X-ray diffraction patterns indicate that the samples possess single phase cubic spinel structure. The lattice constant initially increases for x ≤ 0.3 and thereafter for x > 0.3 it decreases with increasing x. The saturation magnetization (Ms), magneton number (n_B) and coercivity (Hc) decreases with increasing Cr-Zn content x. Curie temperature deduced from AC susceptibility data decreases with increasing x.     

Growth and characterization of chemical bath deposited Cd1−xZnxS thin films

Cd_1−xZn_xS (0 ≤ x ≤ 1) thin films have been deposited by chemical bath deposition method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 80 ± 5 °C and after annealed at 350 °C. The structural, morphological, compositional and optical properties of the deposited Cd_1−xZn_xS thin films have been studied by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) and UV-vis spectrophotometer, respectively. X-ray diffraction analysis shows that for x < 0.8, the crystal structure of Cd_1−xZn_xS thin films was hexagonal structure. For x > 0.6, however, the Cd_1−xZn_xS films were grown with cubic structure. Annealing the samples at 350 °C in air for 45 min resulted in increase in intensity as well as a shift towards lower scattering angles. The parameters such as crystallite size, strain, dislocation density and texture coefficient are calculated from X-ray diffraction studies. SEM studies reveal the formation of Cd_1−xZn_xS films with uniformly distributed grains over the entire surface of the substrate. The EDX analysis shows the content of atomic percentage. Optical method was used to determine the band gap of the films. The photoluminescence spectra of films have been studied and the results are discussed.     

Effect of A site and B site doping on structural, thermal, and dielectric properties of BiFeO3 ceramics

Polycrystalline Bi_1−xBa_xFe_1−yM_yO₃ (M = Co and Mn; x = 0.1, y = 0.1) were synthesized by solid-state route method to study the compositional driven structural transformations in multiferroics. Room temperature X-ray diffraction patterns confirmed the formation of perovskite structure. Rietveld-refined crystal structure parameters revealed the existence of rhombohedral R3c symmetry for both the samples. The samples were found to be nearly free from any other secondary phases. Raman analysis reveals that Ba atom substitutes Bi site and Mn and Co atom substitutes Fe site into the BiFeO₃ with the shifting of phonon modes. The red shift is attributed to Co or Mn doping where as blue shift occurs from Ba doping. The differential scanning calorimetry reveals the corresponding Neel temperature 370 °C and 326 °C for Co and Mn doped samples. Ba and Co substitution with x = 0.1 and y = 0.1 has not affected the Neel temperature of the parent BiFeO₃ as well of Ba and Mn substitution. The variation of frequency dispersion in permittivity and loss pattern due to A-site and B-site substitution in BiFeO₃ was observed in the dielectric response curve.     

High-Q microwave dielectrics in the (Mg1−xZnx)Al2O4 (x = 0-0.1) system

The microwave dielectric properties and the microstructures of (Mg_1−xZn_x)Al₂O₄ (x = 0-0.1) ceramic system prepared by the conventional solid-state route were investigated. The forming of spinel-structured (Mg_1−xZn_x)Al₂O₄ (x = 0-0.1) solid solutions was confirmed by the XRD patterns and the measured lattice parameters, which linearly varied from a = b = c = 8.0815 Å for MgAl₂O₄ to a = b = c= 8.0828 Å for (Mg_0.9Zn_0.1)Al₂O₄. By increasing x, the Q × f of (Mg_1−xZn_x)Al₂O₄ can be tremendously boosted from 82,000 GHz at x = 0 to a maximum of 156,000 GHz at x = 0.05. The Zn substitution was effective in reducing the dielectric loss without detrimental effects on the ?_r and τ_f values of the ceramics.     

Properties of praseodymium-doped bismuth potassium titanate (Bi0.5K0.5TiO3) synthesised using the soft combustion technique

Bismuth potassium titanate (Bi_0.5K_0.5TiO₃; BKT) and praseodymium-doped BKT (Bi_0.5(1−x)Pr_xK_0.5TiO₃; BPKT) powders were synthesised using the soft combustion technique. Fine particles of 10-100 nm of BKT and BPKT were produced. A single phase BKT was obtained with a minimum of 0.5 mol of glycine. Various compounds of Bi_0.5(1−x)Pr_xK_0.5TiO₃ where x = 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20 were prepared. Pure BKT and BPKT powders were obtained after calcination at 800 °C for 3 h. After sintering at 1050 °C for 5 h, pure BKT and BPKT pellets were obtained for x = 0 and 0.01. However, for BPKT with x = 0.03, 0.05, 0.10, 0.15 and 0.20, a minor amount of Bi₄Ti₃O₁₂ (BIT) secondary phase was present after sintering at 1050 °C for 5 h. The crystallite size and grain size of all the samples followed similar trends, first increasing from x = 0 (undoped BKT) to x = 0.05 and then decreasing above x = 0.05. Among the undoped and doped samples, BPKT with x = 0.05 had the highest dielectric properties (?_r = 713.87) due to its large crystallite size (68.66 nm), large grain size (∼435 nm) and high relative density (93.39%).     

Dielectric properties and crystal structure of La(Mg1/2Ti1/2)O3 ceramics with Mg substituted by Co

Solid solutions of (1 − x)La(Co_1/2Ti_1/2)O₃-xLa(Mg_1/2Ti_1/2)O₃ were used to prepare La(Mg_1−xCo_x)_1/2Ti_1/2O₃ using solid-state synthesis. X-ray diffraction patterns of the sintered samples revealed single phase formation. A maximum density of 6.01 g/cm³ was obtained for La(Mg_1−xCo_x)_1/2Ti_1/2O₃ (x = 1) ceramics sintered at 1375 °C for 4 h. The maximum values of the dielectric constant (?_r = 29.13) and the quality factor (Q × f = 80,000 GHz) were obtained for La(Mg_1−xCo_x)_1/2Ti_1/2O₃ with 1 wt% ZnO additive sintered at 1375 °C for 4 h. The temperature coefficient of resonant frequency τ_f was −59 ppm/°C for x = 0.3.     

Crystal structure and dielectric properties of La(Mg1−xZnx)1/2Ti1/2O3 ceramics at microwave frequencies

Ceramics in the system La(Mg_1−xZn_x)_1/2Ti_1/2O₃ with B₂O₃ additions (1 wt.%) have been investigated by the conventional solid-state route. The XRD patterns of the sintered samples (0.3 ≤ x ≤ 1.0) revealed single phase formation with a structure. The unit cell volume slightly increased with increasing Zn content (x). La(Mg_1−xZn_x)_1/2Ti_1/2O₃ were found to form perovskite solid solutions in the whole compositional range. The maximum values of the dielectric constant and the quality factor multiples resonant frequency (Q × f) can be obtained when the La(Mg_0.7Zn_0.3)_1/2Ti_1/2O₃ with 0.5 wt.% B₂O₃ additive were sintered at 1475 °C for 4 h. The temperature coefficient of resonant frequency τ_f (−63 ppm/°C) was measured for x = 0.7.     

The photocatalytic activity of sprayed Zn1 − xMgxO thin films

ZnO has received much attention in the degradation and complete mineralization of environmental pollutants. For the purpose of increasing the photocatalytic efficiency of ZnO, Mg was doped into ZnO thin films.Zn_1 − xMg_xO thin films were prepared by spray pyrolysis method on glass substrates. The deposition temperature was 500 °C. Mg concentration was varied in the range of 0.0 to 0.3 in intervals of 0.05. The pure ZnO films were polycrystalline with preferred orientation (100). Zn_1 − xMg_xO becomes amorphous with increasing Mg concentration. The optical band gap of Zn_1 − xMg_xO changes from 3.26 to 3.59 eV with increasing Mg content. Also, the photocatalytic activity increased with Mg, and the film with x = 0.3 showed the best result.     

Effect of Ag-doping on crystal structure and high temperature thermoelectric properties of c-axis oriented Ca3Co4O9 thin films by pulsed laser deposition

Ag-doped Ca₃Co₄O₉ thin films with nominal composition of Ca_3−xAg_xCo₄O₉ (x = 0∼0.4) have been prepared on sapphire (0 0 0 1) substrates by pulsed laser deposition (PLD). Structural characterizations and surface chemical states analysis have shown that Ag substitution for Ca in the thin films can be achieved with doping amount of x ≤ 0.15; while x > 0.15, excessive Ag was found as isolated and metallic species, resulting in composite structure. Based on the perfect c-axis orientation of the thin films, Ag-doping has been found to facilitate a remarkable decrease in the in-plane electrical resistivity. However, if doped beyond the substitution limit, excessive Ag was observed to severely reduce the Seebeck coefficient. Through carrier concentration adjustment by Ag-substitution, power factor of the Ag-Ca₃Co₄O₉ thin films could reach 0.73 mW m⁻¹ K⁻² at around 700 K, which was about 16% higher than that of the pure Ca₃Co₄O₉ thin film.     

Structural, optical and electrical properties of N-doped ZnO thin films prepared by thermal oxidation of pulsed filtered cathodic vacuum arc deposited ZnxNy films

In this study, N-doped ZnO thin films were fabricated by oxidation of Zn_xN_y films. The Zn_xN_y thin films were deposited on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) using metallic zinc wire (99.999%) as a cathode target in pure nitrogen plasma. The influence of oxidation temperature, on the electrical, structural and optical properties of N-doped ZnO films was investigated. P-type conduction was achieved for the N-doped ZnO obtained at 450 °C by oxidation of Zn_xN_y, with a resistivity of 16.1 Ω cm, hole concentration of 2.03 × 10¹⁶ cm⁻³ and Hall mobility of 19 cm²/V s. X-ray photoelectron spectroscopy (XPS) analysis confirmed the incorporation of N into the ZnO films. X-ray diffraction (XRD) pattern showed that the films as-deposited and oxidized at 350 °C were amorphous. However, the oxidized films in air atmosphere at 450-550 °C were polycrystalline without preferential orientation. In room temperature photoluminescence (PL) spectra, an ultraviolet (UV) peak was seen for all the samples. In addition, a broad deep level emission was observed.