Reactive Hot Pressing and Properties of Zr1−xTixB2–ZrC Composites

Reactive hot pressing was used to prepare Zr_1?xTi_xB₂–ZrC composites with advantageous microstructure and mechanical properties from ZrB₂–TiC powders. The reaction mechanisms and the effects of different levels of TiC on the physical and mechanical properties of the resulting composite were explored in detail and compared to conventionally hot‐pressed ZrB₂ and ZrB₂–ZrC. Incorporation of 10 to 30 vol% TiC enabled full densification and restrained grain growth, reducing the final average grain size from 5.6 μm in pure ZrB₂ to a minimum of 1.4 μm in samples with 30 vol% TiC. The flexural strengths and hardnesses of the composites sintered with TiC were consequently greater than the conventionally processed ZrB₂–ZrC materials, increasing from 440 MPa and 17.4 GPa to a maximum of 670 MPa and 24.2 GPa at 10 vol% TiC. However, despite a decrease in the total average grain size, the flexural strength at higher TiC levels was limited by an increase in ZrC grain growth, which was observed to determine the flexural strength of the reaction sintered composites similar to the case of ZrB₂–SiC.     

Magnetism and Transport Properties of Sr2Ru1−xCoxO4 with x ≤ 0.25

Single‐phase polycrystalline Sr₂Ru_1?xCo_xO₄ are successfully synthesized by conventional solid‐state method with doping content up to x = 0.25. Ferrimagnetism develops among the incommensurate antiferromagnetic fluctuations in the doped compounds. An abnormal coercivity–temperature relation at a high doping level (x > 0.10), in which the samples have smaller coercive field at low temperature than that at high temperature, i.e., H_C(5 K) < H_C(50 K), is observed. The Curie–Weiss temperature shows the negative value for all samples, and the susceptibility increases with Co doping content x. The exchange bias effect is detected in magnetic hysteresis loops. A three‐dimensional transport property has been derived based on the variable rang hopping theory, indicating a thermally assisted hopping of electrons between the localized states.     

Structural and Thermodynamics Properties of TiC1−xNx–TiO1−xNx Solid Solutions: X‐ray Diffraction and First‐Principles Approaches

The structural properties and mixing thermodynamic of TiC_1?xN_x and TiO_1?xN_x (0 ≤ x ≤ 1) solid solutions have been studied by X‐ray diffraction method and first‐principles calculations. The TiC_1?xN_x and TiO_1?xN_x compounds were synthesized via solid‐state reaction and the analysis of XRD patterns show the properties of continuous solid solutions over the whole composition range. Thermodynamic analyses and structural stability studies were performed based on the mixing enthalpies and electronic structures. The mixing enthalpies of TiC_1?xN_x and TiO_1?xN_x can be fitted using a second‐degree polynomial with the increasing of supercell. The first‐principles calculations results reveal that the TiO_1?xN_x shows large number vacancies segregated in TiO‐part. The charge redistributed around Ti vacancy constitutes the main contribution to the stabilization rather than the Ti–Ti bond across the O vacancy through analyzing the electron density difference plots and PDOS . These results provide theoretical basis for the development and application of the TiC_1?xN_x and TiO_1?xN_x solid solutions.     

Nanocomposites Based on Polyethylene and Polyhedral Oligomeric Silsesquioxanes, 1 – Microstructure,Thermal and Thermomechanical Properties

Nanocomposites of linear low‐density polyethylene (LLDPE), with three different amounts of polyhedral oligomeric silsesquioxanes (POSS), were prepared through melt‐mixing in a batch‐mixer at 150 °C. The structure of the prepared nanocomposites was studied by X‐ray scattering and optical microscopy. The surface morphology of the nanocomposites was investigated through field‐emission SEM. The thermal properties of the pure LLDPE and nanocomposites were studied by differential scanning calorimeter (DSC). Thermomechanical properties were assessed on a Paar‐Physics MCR501 rheometer using a solid‐state rectangular fixture. Results exhibited a significant improvement in both the storage and loss moduli of the neat LLDPE upon the incorporation of the POSS particles. A substantial improvement in thermal stability was also observed in the high‐temperature region.

     

Properties of Ca–(Y)–Si–Al–O–N–F Glasses: Independent and Additive Effects of Fluorine and Nitrogen

Thirty glasses of composition (in equivalent percent) 20‐xCa:xY:50Si:30Al:(100‐y‐z)O:yN:zF, with x = 0, 10; y = 0, 10, 20, and z = 0, 1, 3, 5, 7 were prepared by melting and casting. All glasses were X‐ray amorphous. Glass molar volumes (MV) decreased with nitrogen substitution for oxygen for all fluorine contents and, correspondingly, glass fractional compactness increased. Fluorine substitution of oxygen had virtually no effect on molar volume or fractional glass compactness for the three nitrogen contents tested. Young's modulus and microhardness were virtually unaffected by fluorine substitution for oxygen while nitrogen substitution for oxygen caused increases in these two properties. Glass‐transition temperature and dilatometric‐softening point values all decreased with increasing fluorine substitution levels, while increasing nitrogen substitution caused values for these thermal properties to increase. Correspondingly, the thermal expansion coefficient increased with fluorine and decreased with nitrogen substitution levels. Using property value differences between glasses containing fluorine and the corresponding glass containing 0 eq.% F enabled 24 data points to be used to determine the effect of fluorine on T_g,dil and T_DS. The trends were linear with a gradient for both properties of the order of ?22°C (eq.% F)^?1. For the nitrogen effect, 20 data points were analyzed for trend effects. As expected from earlier work, all trends had good linearity. Gradients were for T_g,dil and T_DS +2.5°C (eq.% N)^?1, which are fairly similar to previous results in oxynitride systems. All of the data collected and its analysis clearly shows that the substitution effects of fluorine for oxygen and nitrogen for oxygen are independent and additive with the fluorine substitution. The property trends of the glasses are discussed in terms of their implications for glass structure.     

Synthesis and Electrochemical Properties of BaFe1−xCuxO3−δ Perovskite Oxide for IT‐SOFC Cathode

A series of iron‐based perovskite oxides BaFe_1−xCu_xO_3−δ (x = 0.10, 0.15, 0.20 and 0.25, abbreviated as BFC‐10, BFC‐15, BFC‐20 and BFC‐25, respectively) as cathode materials have been prepared via a combined EDTA‐citrate complexing sol‐gel method. The effects of Cu contents on the crystal structure, chemical stability, electrical conductivity, thermal expansion coefficient (TEC) and electrochemical properties of BFC‐x materials have been studied. All the BFC‐x samples exhibit the cubic phase with a space group Pm3m (221). The electrical conductivity decreases with increasing Cu content. The maximum electrical conductivity is 60.9 ± 0.9 S cm⁻¹ for BFC‐20 at 600 °C. Substitution of Fe by Cu increases the thermal expansion coefficient. The average TEC increases from 20.6 × 10⁻⁶ K⁻¹ for BFC‐10 to 23.7 × 10⁻⁶ K⁻¹ for BFC‐25 at the temperature range of 30–850 °C. Among the samples, BFC‐20 shows the best electrochemical performance. The area specific resistance (ASR) of BFC‐20 on SDC electrolyte is 0.014 Ω cm² at 800 °C. The single fuel cell with the configguration of BFC‐20/SDC/NiO‐SDC delivers the highest power density of 0.57 W cm⁻² at 800 °C. The favorable electrochemical activities can be attributed to the cubic lattice structure and the high oxygen vacancy concentration caused by Cu doping.     

Resistivity Enhancement and Transport Mechanisms in (1 − x)BaTiO3–xBi(Zn1/2Ti1/2)O3 and (1 − x)SrTiO3–xBi(Zn1/2Ti1/2)O3

Ceramics of composition (1?x)BaTiO₃–xBi(Zn_1/2Ti_1/2)O₃ (BT‐BZT) were prepared by solid‐state synthesis; they have been shown to exhibit excellent properties suited for high‐temperature dielectric applications. The X‐ray diffraction data showed a single‐phase perovskite structure for all the compositions prepared (x ≤ 0.1 BZT). The compositions with less than 0.075 BZT exhibited tetragonal symmetry at room temperature and pseudo‐cubic symmetry above it. Most notably, a significant improvement in insulation properties was measured with the addition of BZT. Both low‐field AC impedance and high‐field direct DC measurements indicated an increase in resistivity of at least two orders of magnitude at 400°C with the addition of just 0.03 BZT (~10⁷ Ω‐cm) into the solid solution as compared to pure BT (~10⁵ Ω‐cm). This effect was also evident in dielectric loss data, which remained low at higher temperatures as the BZT content increased. In conjunction with band gap measurements, it was also concluded that the conduction mechanism transitioned from extrinsic for pure BT to intrinsic for 0.075 BZT suggesting a change in the fundamental defect equilibrium conditions. It was also shown that this improvement in insulation properties was not limited to BT‐BZT, but could also be observed in the paraelectric SrTiO₃–BZT system.     

Microwave Dielectric Properties,Crystal Structure,and Microstructure of the Bi3Nb1−xTaxO7 Solid Solution

New, commensurate members of the fluorite‐related Bi₃Nb_1?xTa_xO₇ family were synthesized and their crystal structures, microstructures, and microwave (MW) dielectric properties were characterized. The incorporation of Ta into the tetragonal Bi₃Nb_1?xTa_xO₇ solid solution was found to gradually affect the density and the MW dielectric properties. The materials sintered at 870°C exhibited relative permittivities in the range k′ = 86–72, Q × f values from 793 to 1189 GHz and a positive temperature coefficient of resonant frequency from 88 to 12 ppm/K. The formation of the members of the fluorite‐related solid solution along the Bi₃Nb_1?xTa_xO₇ composition depends on a phase transition, and thus their properties are compared within the compositional range. The correlations between their MW dielectric properties, compositions, crystal structures, and processing parameters were discussed in detail. Optimization of MW properties can be achieved by utilizing the ability of the Bi₃Nb_1?xTa_xO₇ solid solution that it undergoes a phase transformation from cubic to tetragonal structure which are both characterized by unique properties, under certain synthesis conditions.     

ZrB2–ZrCxN1−x Eutectic Composites Produced by Melt Solidification

Ceramic eutectics are naturally occurring in‐situ composites and can offer superior mechanical properties. Here, ZrB₂–ZrC_xN_1?x quasi‐binary ceramic eutectic composites were produced by arc‐melting a mixture of ZrB₂, ZrC, and ZrN powders in an N₂ atmosphere. The arc‐melted ZrB₂–ZrC_xN_1?x composites containing 50 mol% of ZrB₂ (irrespective of the ZrC/ZrN ratio) showed rod‐like eutectic structures, where ZrC_xN_1?x single‐crystalline rods were dispersed in the ZrB₂ single‐crystalline matrices. Multiple orientation relationships between the ZrC_xN_1?x rods and the ZrB₂ matrices were observed, and one was determined as ZrB₂ {} //Zr_xN_1?x {111} and ZrB₂ < > //ZrC_xN_1?x < > . The rod‐like eutectic composites had higher hardness than the hypo‐ and hypereutectic composites and the 50ZrB₂–40ZrC–10ZrN (mol%) eutectic composite showed the highest Vickers hardness (H_v) of 19 GPa.     

Enhanced Multiferroic and Magnetocapacitive Properties of (1 − x)Ba0.7Ca0.3TiO3–xBiFeO3 Ceramics

The structures, Curie temperature, dielectric relaxor behaviors, ferroelectricity, ferromagnetism, and magnetocapacitance of the (1?x)Ba_0.70Ca_0.30TiO₃–xBiFeO₃ [(1?x)BCT–xBF, x = 0–0.90] solid solutions have been systematically investigated. The ceramics have coexisted tetragonal (T) and orthorhombic (O) phases when x ≤ 0.06, coexisted pseudocubic (PC) and O phases when x = 0.065, coexisted cubic and O phases when 0.07 ≤ x ≤ 0.12, PC phase when 0.21 ≤ x ≤ 0.42, coexisted T and rhombohedral (R) phases when 0.52 ≤ x ≤ 0.70, and R phase when x ≥ 0.75. Significantly, composition‐dependent microstructures and Curie temperature are observed, the average grain size increases from 1.9 μm for x = 0, reaches 12.0 μm for x = 0.67, and then decreases to 1.3 μm for x = 0.90. At room temperature, the ceramics with x = 0.42–0.70 show piezoelectric properties and multiferroic behaviors, characterized by the polarization‐electric field, polarization current intensity–electric field, and magnetization–magnetic field curves, the composition with x = 0.67 has maximum polarization, remnant polarization, maximum magnetization, and remnant magnetization of 15.0 μC/cm², 9.1 μC/cm², 0.33 emu/g, and 0.14 emu/g, respectively. In addition, the magnetocapacitance is evidenced by the increased relative dielectric constant with increasing the applied magnetic field (H). With ΔH = 8 kOe, the composition with x = 0.67 shows the largest values of (ε_r(H) ? ε_r(0))/ε_r(0) = 2.96% at room temperature. The structure–property relationship is discussed intensively.     

Microwave Absorption of SiC/HfCxN1−x/C Ceramic Nanocomposites with HfCxN1−x‐Carbon Core–Shell Particles

The dielectric properties of high‐temperature stable single‐source precursor‐derived SiC/HfC_xN_1?x/C ceramic nanocomposites are determined by microwave absorption in the X‐band (8.2–12.4 GHz) at room temperature. The samples synthesized at 1700°C, denoted as SiC/5HfC_xN_1?x/C‐1700°C and SiC/15HfC_xN_1?x/C‐1700°C ceramics, comprising ≈ 1.3 and ≈ 4.2 vol% HfC_xN_1?x, respectively, show enhanced microwave absorption capability superior to hafnium‐free SiC/C‐1700°C. The minimum reflection loss of SiC/5HfC_xN_1?x/C‐1700°C and SiC/15HfC_xN_1?x/C‐1700°C are ?47 and ?32 dB, and the effective absorption bandwidth amount to 3.1 and 3.6 GHz, respectively. Segregated carbon, including graphitic carbon homogeneously dispersed in the SiC matrix and less ordered carbon deposited as a thin film on HfC_xN_1?x nanoparticles, accounts for the unique dielectric behavior of the SiC/HfC_xN_1?x/C ceramics. Due to their large reflection loss and their high chemical and temperature stability, SiC/5HfC_xN_1?x/C‐1700°C and SiC/15HfC_xN_1?x/C‐1700°C ceramics are promising candidate materials for electromagnetic interference applications in harsh environment.     

Long‐Range Ordered Structure of Ti–B–C–N in a TiB2–TiCxN1−x Eutectic Composite

A TiB₂–TiC_xN_1?x quasi‐binary eutectic composite, with a rod‐like faceted texture and a long‐range ordered structure of Ti–B–C–N, was prepared by the arc‐melting of TiB₂, TiC, and TiN powders. Hexagonal single‐crystalline TiC_xN_1?x rods were grown in a single‐crystalline TiB₂ matrix with a crystal orientation relationship of TiB₂ //TiC_xN_1?x and TiB₂ [0001]//TiC_xN_1?x [111]. A long‐range ordered structure of Ti–B–C–N was formed by the intermixing of the coherent interplanar spacings of seven TiB₂ (0001) and nine TiC_xN_1?x (111) planes.     

Defective Y2O3−x–driven anomalous photocatalytic enhancement using Y2O3−x–TiO2−x nanorod composite composition spreads

Synergistic photocatalysis is reported, using the optimal amounts of oxygen vacancies of high‐k materials and nanoarchitecture maneuvering by employing a combinatorial sputtering approach. The highlights include (i) the successful fabrication of samples using combinatorial sputtering; (ii) a systematic investigation of the coupling effect between Y₂O_3?x and TiO_2?x; (iii) elucidating charge carrier transport through current‐voltage (I‐V) and capacitance‐voltage (C‐V) characterizations; and (iv) providing an alternative application for high‐dielectric constant (high‐k) materials in photocatalysis. The simple yet effective composition spread technique rapidly determined that Sample 6 (4 at% Y₂O_3?x‐96 at% TiO_2?x, TiO_2?x‐rich on the Y₂O_3?x–TiO_2?x nanorod composite composition spread) exhibited the highest photocatalytic efficiency (i.e., approximately 3.4 times and 1.4 times higher than that of P25 and pure TiO_2?x nanorods, respectively). The predominant factor was determined to be electron migration along defective Y₂O_3?x nanorods to the sample surface. The extracted mobility was discovered to be an order of magnitude greater than that of pure TiO_2?x. The photoelectrochemical stability and reusability were also demonstrated.     

Significant Improvement of Superconducting Properties in Nano‐NiFe2O4‐Doped Y–Ba–Cu–O Single‐Grain Superconductor

Introduction of refined second‐phase particles in superconducting YBa₂Cu₃O_7?x (Y‐123) matrix is known to be an effective route to improve the δl‐type pinning and the performance of Y–Ba–Cu–O (YBCO) single‐grain superconductors, while the δT_c‐type pinning induced by spatial fluctuations in matrix composition is also important and contributes to the in‐field J_c performance and high‐field applications of bulk superconductors. In this communication, chemical doping of nano‐sized NiFe₂O₄ (mean size 50 nm) in single‐grain YBCO superconductor is performed using a novel top‐seeded infiltration growth (TSIG) technique based on a solid source pellet (SSP) of nano‐Y₂O₃ + BaCuO₂. The results indicate that, significant improvement of bulk performances including levitation force (33.93 N) and trapped field (0.3628 T) has been observed in the 0.2 wt% nano‐NiFe₂O₄‐doped sample, which are much higher than the undoped sample (28.81 N and 0.2754 T). T_c measurement indicates that, a decreased onset T_c of about 87.5 K and a broadened transition width of about 5 K are observed in the NiFe₂O₄‐doped sample, indicating appearance of weak superconducting regions in superconducting matrix caused by Ni and Fe substitutions in Y‐123 crystal lattice. This study supplies a practical approach to increase the YBCO bulk performance significantly.     

Structural and Piezoelectric Properties of (1−x)Pb(Zr1−yTiy)O3–xPb(Zn0.4Ni0.6)1/3Nb2/3O3 Ceramics Near Triple Point

The crystal structure and piezoelectric properties of (1?x)Pb(Zr_1?yTi_y)O₃‐xPb(Zn_0.4Ni_0.6)_1/3Nb_2/3O₃ [(1?x)PZ_1?yT_y‐xPZNN] ceramics were investigated. The 0.665PZ_0.45T_0.55‐0.335PZNN ceramic has the triple point composition, where the rhombohedral, pseudocubic, and tetragonal structures coexist. Maximum d₃₃ and k_p values of 770 pC/N and 0.69, respectively, were observed from this specimen; it also exhibited a large ε^T₃₃/ε_o value of 3250. Although the maximum d₃₃ value was obtained from the triple point composition specimen, its g₃₃ and d₃₃ × g₃₃ values were relatively small because of its large ε^T₃₃/ε_o value. However, the 0.665PZ_0.46T_0.54‐0.335PZNN ceramic, which has a rhombohedral structure, exhibited a large g₃₃ value of 43 × 10^?3 Vm/N and a d₃₃ × g₃₃ value of 27 000 × 10^?15 m²/N. Therefore, this ceramic is a good candidate for multilayer actuators and piezoelectric energy harvesters.     

Variation of Band Gap and Lattice Parameters of β−(AlxGa1−x)2O3 Powder Produced by Solution Combustion Synthesis

Single‐phase monoclinic aluminum–gallium oxide powders, β?(Al_xGa_1?x)₂O₃, have been produced by solution combustion synthesis for Al fraction 0 ≤ x < 0.8. α?(Al_xGa_1?x)₂O₃ is observed for x = 1, with mixed α + β for x = 0.8. The contraction in lattice parameters and increase in band gap with increasing Al concentration were characterized by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS), respectively, and are compared with a first‐principles density‐functional theory calculation. A novel filtering procedure is described to reduce the uncertainty involved in measuring band gap using photoemission, and to remove asymmetry in XPS line shapes caused by differential charging of loose powder. The lattice parameters vary linearly with Al fraction, but exhibit a change in slope at x = 0.5 that is attributed to the difference between aluminum occupying tetrahedral and octahedral sites in the monoclinic lattice. The band gap changes linearly with local stoichiometry, including increasing when aluminum content at the surface is enriched relative to the interior, with a range of over 1.8 eV.     

Structural Investigation and Functional Properties of MgxNi1−xFe2O4 Ferrites

The preparation, structural, microstructural, dielectric, and low temperature magnetic properties of Mg_xNi_1?xFe₂O₄ (x = 0, 0.17, 0.34, 0.50, 0.66, 0.83, 1) ferrites synthesized by using a self‐combustion sol–gel method is presented. Good insulating properties were found for all the compositions at high frequencies (kHz and MHz range), which might drive the present ceramics as interesting for RF/microwaves applications. By increasing the Mg²⁺ concentration, the total resistivity strongly increases (from ~10⁶ Ωm for the Ni ferrite to 10⁹ Ωm for the Mg ferrite), corresponding to conductivities in the range 10^?9–10^?6 S/m at f = 1 Hz. Typical ferrimagnetic character with a small coercivity and saturation magnetization in the range (30–50) Am²/kg, which slightly decreases with increasing the Mg content, were found. On the basis of the combined results from the infrared spectroscopy and XRD analysis, it was shown that the magnetic properties depend on the Mg²⁺ ions distribution on the octahedral and tetrahedral sites and the experimental saturation magnetization allowed to compute the cation distribution for the Mg_xNi_1?xFe₂O₄ ferrites.     

Investigation on Crystallization and Optical Properties of Ca1−xLaxF2+x Glass‐Ceramics

Transparent oxyfluoride glass‐ceramics containing Er³⁺, Yb³⁺:Ca_1?xLa_xF_2+x nanocrystals, which may have potential applications in the fields of solid‐state laser and luminescence, were prepared. Crystallization of Ca_1?xLa_xF_2+x and behavior of Yb³⁺ and Er³⁺ during the heat treatment was investigated. Results showed that alumina content had a significant effect on crystallization of Ca_1?xLa_xF_2+x in the SiO₂–Al₂O₃–CaF₂–LaF₃ system. Due to the size of phase‐separated areas, the size of the crystals during the heat treatment did not change significantly. After crystallization of Ca_1?xLa_xF_2+x in the glass, the majority of Er³⁺ ions incorporated into the Ca_1?xLa_xF_2+x crystals during the heat‐treatment process. Time‐resolved luminescence of Er³⁺ ions in the samples around 842 nm showed that the solubility of Er³⁺ ions in Ca_1?xLa_xF₃ crystals is higher than pure CaF₂ crystals. The glass undergoes an enormous phase separation, which keeps the Yb³⁺ ions within the other separated phase. Therefore, only at high temperatures (790°C) or with a long heat‐treatment time (72 h), there is a possibility for Yb³⁺ ions to be incorporated into the fluorine phase.     

Structural and Mössbauer Investigation of Nanocrystalline SrFe1−xTixO3−δ

Crystal structure and cation distribution of nanocrystalline SrFe_1?xTi_xO_3?δ (0 ≤ x ≤ 0.3) synthesized by combined high‐energy ball milling and solid‐state reactions are investigated using Neutron powder diffraction and Mössbauer spectroscopy. Ti doping stabilizes the single phase tetragonal structure with I4/mmm space group up to x = 0.3. The neutron and Mössbauer data confirm that Fe exists in three different sites both crystallographically as well as magnetically in all the four compositions. The cation distribution at various sites is established through Rietveld refinement.     

Tailoring Strain Properties of (0.94−x)Bi1/2Na1/2TiO3–0.06BaTiO3–xK0.5Na0.5NbO3 Ferroelectric/Relaxor Composites

A remarkable progress in the quest of lead‐free piezoceramics for actuator applications has been made with the development of incipient piezoceramics featured by giant strains. A drawback, however, is the high electric field required to generate this giant strain. A powerful approach to overcoming this drawback lies in relaxor/ferroelectric (FE) composites comprised such giant strain materials (matrix) and a FE or nonergodic relaxor (seed). In this study, we investigate the effect of K_0.5Na_0.5NbO₃ content in the matrix and the volume ratio of seed to matrix using composites of 0.93Bi_1/2Na_1/2TiO₃–0.07BaTiO₃ as a seed and (0.94 ? x)Bi_1/2Na_1/2TiO₃–0.06BaTiO₃–xK_0.5Na_0.5NbO₃ as a matrix. The strain of all matrices, independent of their K_0.5Na_0.5NbO₃ content, was found to be enhanced by adding a certain amount of seed. An optimum strain is achieved for the composite comprised of a matrix with x = 0.02 K_0.5Na_0.5NbO₃ and 10% seed. By means of a differential analysis on the temperature‐dependent dielectric permittivity, it was shown that the seed phase is still present in the composites despite the naturally expected diffusion process during sintering.