Two-step Solid-state Reaction Research Articles

Cathode performance of novel γ-LixV2O5/carbon composite in organic and aqueous electrolyte

Preparation of in-situ composites with carbon by pyrolysis of an organic precursor is an effective strategy to improve performances of insulating and semiconducting cathode materials. However, due to the property of organic precursor to act as a strong reductive agent during carbonization process, the in-situ synthesis of LiV2O5/C composite cathode material is delicate and presents a challenge for researchers, since vanadium in LiV2O5 coexists in two oxidation states, V4+ and V5+. In our research, we utilized an adopted conventional solid state method for the in-situ preparation of LixV2O5/C composite (x ≈ 0.86). By using methylcellulose polymer as a carbon source, LixV2O5/C was synthesized via two-step solid state reaction at elevated temperatures. LixV2O5 crystallized as gamma polymorph phase, and the amount of in-situ formed carbon does not exceed 3wt%. The electrochemical characteristics of the as-prepared LixV2O5/C were investigated in aqueous and non-aqueous electrolyte via cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) tests and electrochemical impedance spectroscopy (EIS). On lithium insertion/removal, the LixV2O5/C composite exhibits stable cycling performance and achieves significant storage capacity enhancement when compared to pristine LixV2O5 obtained under similar conditions. Under current densities of 0.1, 0.2, 0.3 and 1 A/g, the specific capacity enhancement is around 112, 91, 80 and 62 %, respectively. Replacing the organic electrolyte with the aqueous one has a negligible effect on the mechanism and efficiency of lithium intercalation within the LixV2O5/C, which opens up the possibility of using this material in aqueous as well as in organic-electrolyte batteries. The decay of cathode's activity evidenced during electrochemical exchange of lithium with sodium in aqueous environment comes as a result of the formation of electrochemically inactive β-NaxV2O5.

Comparative investigation of low and high pelletize pressure for (Ag)x/CuTl-1223 nanoparticles-superconductor composites

This article experimentally investigates the impact of silver (Ag) nano-particles inclusion and high pelletized pressure on the structural, morphological, and electrical properties of Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (noted CuTl-1223) bulk system. The nano-(Ag) x /CuTl-1223 composites were synthesized using a two-step solid-state reaction process with added amount of Ag nano-particles ranging from 0 to 2.0 wt% of the total mass. These nano-composites were produced at both low and high pelletize pressure of 0.202 GPa. All prepared samples were characterized using valuable techniques such as X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR), and dc-resistivity measurement at low as well as high pelletized pressure, respectively. The structural investigation via the XRD technique indicated that Ag NPs did not affect the CuTl-1223 tetragonal structure, confirmed that Ag nano-particles were settled across the grain boundaries. SEM examination revealed a fine distribution of nano-sized silver (Ag) NPs among the CuTl-1223 grains, as well as improved weak-links and density of void/pores. The position of distinct vibrational oxygen modes in FTIR spectra showed no substantial alteration, indicating that the structural nature of the host CuTl-1223 phase was preserved. The electrical properties were studied using the four-point probe technique, and the activation energy were determined using Arrhenius law. The results of measurements showed that pelletization pressure of 0.202 GPa have an impact on the critical temperature of (Ag) x /CuTl-1223 composites. The superconducting critical temperature was enhanced from 99 K to 107 K at high-pressure of pelletization (0.202 GPa) as compared to low pressure, with = 0 ∼ 2.0 wt nano-particles addition to the host CuTl-1223 phase.

Origin of high comprehensive electromechanical properties of novel donor and acceptor–codoped PMN–30PT ceramics

Donor and acceptor–codoped PMN–30PT ceramics with 1–3 mol% Sm and 1 mol% Mn were fabricated via a two-step solid-state reaction. The crystal structure and electrical properties were investigated in detail. Donor Sm and acceptor Mn codoping substantially enhances the electromechanical, piezoelectric, and dielectric properties with a high piezoelectric coefficient d33 = 483–680 pC/N, a high mechanical quality factor Qm = 518–642, a high field-induced strain = 0.20%–0.24 %, and a low dielectric loss tan δ = 0.54%–0.69 %. X-ray diffraction and Raman spectra reveal the coexisting triple phase composition of the rhombohedral phase, tetragonal phase, and monoclinic polar nanoregions. Thermally stimulated depolarization current verifies the formation of various defect dipole clusters such as (MnTi″–VO··)×. With enhanced local structure heterogeneity induced by Sm, the phase composition and defect chemistry are regarded as the origin of such high comprehensive performance.

The effects of Eu3+ doping on the piezoelectric property and temperature stability of the 0.15PSN-0.52PMN-0.33PT ceramics

We successfully prepared Eu2O3 doped 0.15PSN-0.52PMN-0.33PT ceramics through two-step solid state reaction, and carefully studied their phase structure, microstructure, electric performance and temperature stability. It is found that Eu3+ doped PSN-PMN-PT ceramics exhibit greatly improved piezoelectrical performance. When the Eu2O3 content is 0.02 mol, the ceramic shows the best synthetical properties: d33 = 859 pC/N, d33 * = 1078 pm/V, Ec= 5.18 kV/cm, and Tm = 139 °C. Compared with the undoped matrix ceramic, the d33 increases by nearly 78%, meanwhile, its variation rate is only 18% as the temperature rises from room temperature to 130 °C. Our results indicate that Eu3+ doped 0.15PSN-0.52PMN-0.33PT ceramics have promising candidate for practical applications.

Thermoelectric performance of Mg2.2(Ge0.9Sn0.1) ternary solid solution doped with Ag, Bi, Ni and Sb

Mg2.2(Ge0.9Sn0.1)0.94X0.06(X = Ag, Bi, Ni, Sb) ternary solid solutions were synthesized using a two-step solid state reaction followed by hot pressing. The effects elemental doping on thermoelectric properties of these compounds were studied in the temperature range of 300 to 800 K. The findings demonstrate that Bi, Sb, and Ni function as useful n-type dopants, with Bi being more efficiently in the solid solution of Mg2.2Ge0.9Sn0.1. Additionally, the findings indicate that Ag is less efficient in n-type doping. Finally, maximum ZT for the Bi-doped sample is 0.82 at 800 K because of its strong electrical conductivity and moderate Seebeck coefficient.

From Layered Antiferromagnet to 3D Ferromagnet: LiMnBi-to-MnBi Magneto-Structural Transformation

The intermetallic compound LiMnBi was synthesized by the two-step solid-state reaction from the elements. A synthesis temperature of 850 K was selected based on in situ high-temperature powder X-ray diffraction data. LiMnBi crystalizes in the layered-like PbClF structure type (a = 4.3131(7) Å, c = 7.096(1) Å at 100 K, P4/nmm space group, Z = 2). The LiMnBi structure is built of alternating [MnBi] and Li layers, as determined from single-crystal X-ray diffraction data. Magnetic property measurements and solid-state 7Li nuclear magnetic resonance data collected for polycrystalline LiMnBi samples indicate the long-range antiferromagnetic ordering of the Mn sublattice at ∼340 K, with no superconductivity detected down to 5 K. LiMnBi is air- and water-sensitive. Under aerobic conditions, Li can be extracted from the LiMnBi structure to form Li2O/LiOH and MnBi (NiAs structure type, P63/mmc). The obtained MnBi polymorph was previously reported to be one of the strongest rare-earth-free ferromagnets, yet its bulk synthesis in powder form is cumbersome. The proposed magneto-structural transformation from ternary LiMnBi to ferromagnetic MnBi involves condensation of the MnBi4 tetrahedra upon Li deintercalation and is exclusive to LiMnBi. In contrast, ferromagnetic MnBi cannot be obtained from either isostructural NaMnBi and KMnBi or from the structurally related CaMn2Bi2. Such a distinctive transformation in the case of LiMnBi is presumed to be due to its fitting reactivity to yield MnBi and a favorable interlayer distance between [MnBi] layers, while the interlayer distance in NaMnBi and KMnBi structural analogues is unfavorably long. The studies of delithiation from layered-like LiMnBi under different chemical environments indicate that the yield of MnBi depends on the type of solvent used and the kinetics of the reaction. A slow rate and mild reaction media lead to a high fraction of the MnBi product. The saturation magnetization of the “as-prepared” MnBi is ∼50% of the expected value of 81.3 emu/g. Overall, this study adds a missing member to the family of ternary pnictides and illustrates how soft-chemistry methods can be used to obtain “difficult-to-synthesize” compounds.

Synthesis and electromagnetic wave absorption performances of a novel (Mo0.25Cr0.25Ti0.25V0.25)3AlC2 high-entropy MAX phase

• A new two-step solid state reaction process was proposed to synthesize single-phase high-entropy MAX phases. • A novel (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 high-entropy MAX phase was successfully prepared. Investigations on electromagnetic (EM) wave absorption properties and effects of oxidation on EM wave absorption performances of (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 were conducted for the first time. • (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders exhibit excellent EM wave absorption properties, whose minimum reflection loss value can reach -45.80 dB (at 1.7 mm thickness) and maximum effective absorption bandwidth is 3.60 GHz (at 1.5 mm thickness). • After oxidation at 400-800°C, (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 can retain good EM wave absorption properties in a certain frequency range. Herein, a novel kind of high-entropy MAX phases, (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders were successfully synthesized by a newly proposed two-step solid state reaction process. The oxidation experiments demonstrate that the oxidation products of Al 2 Mo 3 O 12 and rutile TiO 2 are formed at about 600 and 800 ℃, respectively. Besides, the dielectric and electromagnetic (EM) wave absorption properties of (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders and those after oxidation at different temperatures were also examined. The results show that the as-synthesized (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders possess excellent EM wave absorption performances with the minimum reflection loss ( RL ) of -45.80 dB (at 1.7 mm thickness) and the maximum effective absorption bandwidth ( E AB ) of 3.6 GHz (at 1.5 mm thickness). After oxidation at 400-800 ℃, due to the coupling of conductivity loss and polarization loss, (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders can retain good EM wave absorption properties in a certain frequency range. In this paper, the effects of oxidation on EM wave absorption properties of high-entropy MAX phases were systematically investigated for the first time. This work manifests that high-entropy MAX phases are promising EM wave absorbing candidates and can maintain good EM wave absorption performances after oxidation.

Facile Preparation, Microstructure and Dielectric Properties of La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 Perovskite High-Entropy Ceramics

Preparation and properties of La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 high-entropy ceramics are investigated. La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 high-entropy ceramics are prepared by a traditional two-step solid-state reaction method in air. La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 single-phase powders are synthesized by calcining the mixed oxides at 1000 °C for 20 h. The high-entropy ceramics are sintered at 1350–1650 °C in a muffle furnace for 4 h by using the above powders. The phase compositions of the high-entropy ceramics at different temperatures are characterized by X-ray diffraction (XRD) with Cu Kα radiation. A field-emission scanning electron microscope with energy-dispersive spectroscopy (EDS) is used to observe the microstructures and analyze the elemental distributions. The hardness and dielectric properties are measured and discussed.

Tailoring Li2Si2O5 rod-like particles and their simultaneously strengthening and toughening effects on lithium disilicate glass-ceramics

To achieve high performance of glass-ceramics, it is urgent to open a new path to enhance the mechanical properties. In this study, Li2Si2O5 rods were successfully synthesized by a modified two-step solid-state reaction sintering method. The rod aspect ratio could be controlled by adjusting the second stage sintering time. The evolution process of such Li2Si2O5 rods and their possible formation mechanism were put forward. For the first time, the Li2Si2O5 rods were used to strengthen and toughen the homologous Li2Si2O5 glass-ceramic in a typical quaternary Li2O-SiO2-K2O-La2O3 system, which indicates a high flexural strength and toughness of 315±24 MPa and 2.42±0.6 MPa·m1/2, respectively. In this glass-ceramic, the microstructure features a densely stagger network formed by the elongated rods and smaller Li2Si2O5 crystals in the glass matrix, contributing to the improvement of mechanical properties. The results demonstrate that Li2Si2O5 rods could be an excellent candidate for strengthening and toughening glass-ceramics.

Impact of NiO nano-particles on colossal magneto-resistance of La0.70Ca0.30MnO3 composite

Mixed-valent perovskite manganite has gained considerable research interest due to the increasing demand for energy storage materials. Herein, we show that colossal magneto-resistance properties of La0.7Ca0.3MnO3 (LCMO) can be changed via nickel oxide (NiO) doping. A two-step conventional solid-state reaction method is used to synthesize LCMO-10% NiO composite. The phase purity, structural, electrical (resistivity), and magneto-transport properties of as-synthesized LCMO-10% NiO composite are detailed. NiO doping shifts metal–insulator transition temperature (TMI) from 263 K to 195 K and increases resistivity. The magneto-resistance (MR) measurements showed 10% NiO doping resulted in a maximum MR of ∼ -70.32% at 200 K (near TMI) and 10 T applied magnetic field. However, -0.0849% MR is seen at 290 K (RT) and 0.3 T. The increased ∼ -63.85% MR is found at 100 K and at 10 T, which is comparatively much higher than the pristine LCMO sample. This is due to the addition of NiO in LCMO that improves physical properties (i.e., grain size).

SnO2 modified PNN-PZT ceramics with ultra-high piezoelectric and dielectric properties

In this work, a two-step solid-state reaction method is used to prepare the 0.55 Pb(Ni1/3Nb2/3)O3-0.135PbZrO3-0.315PbTiO3/xSnO2 (PNN-PZT/xSnO2) ceramics. The influences of SnO2 on the crystalline structure, electromechanical properties, and temperature stability of PNN-PZT ceramics were studied in detail. The results demonstrate that the Sn4+ ions are successfully introduced into the PNN-PZT crystalline lattice and substitute B-site Ni2+ and Zr4+. The x = 0.0025 ceramic with the coexistence of rhombohedral, tetragonal, and pseudocubic phases exhibits the optimized comprehensive properties: the quasi-static piezoelectric constant d33, large-signal d33*, electromechanical coupling coefficients kp and kt, free dielectric constant εr, and mechanical quality factor Qm are 1123 pC/N, 1250 p.m./V, 0.63, 0.54, 9529, and 57, respectively. Meanwhile, the Curie temperature for this composition is 103 °C, almost maintaining the same level as the PNN-PZT matrix. After annealing at 75 °C, the retained d33 of x = 0.0025 ceramic is as high as 975 pC/N, superior to the PNN-PZT matrix (retained d33 ≈ 873 pC/N). Our results provide a promising piezoelectric material for board bandwidth, high sensitivity, and miniaturized medical ultrasonic transducers applications.

A correlative study between the microstructure and electrical properties of lead-free piezoceramics (1-x)BHT-xYLG driven by the synergistic action of multiple factors

Piezoceramics are important functional materials with broad applications in electronics, communication, medicine, and energy. Increasing environmental protection and human health concerns about the toxicity of lead have impelled the development of lead-free piezoceramics. At this work, in combination with phase field simulation, grain growth mechanism, ferroelectric domain wall model, and defect dipole formation mechanism, (1-x)Ba(Hf0.02Ti0.98)O3-x(Y0.5Li0.5)GeO3 [(1-x)BHT-xYLG, x = 0–0.40 mol%] lead-free piezoceramics were designed and fabricated via the two-step synthesis and solid-state reaction method, which yielded superior comprehensive electrical property. Phase field simulation respectively simulates the distribution of ferroelectric domains of O and T phase under different external electric fields (0–20 kV/mm) and the phase states under different temperatures (−100 to 150 °C). This research finds that their electrical properties are affected by the synergistic action of multiple factors, e.g., orthorhombic-tetragonal phase boundary (O-T PB), grain size (GS), domain-wall (DW), and defect dipole (DD), etc., rather than any single factor.

Electron density distribution influencing the electrical and magnetic properties of polycrystalline Bi0.9Sm0.1FeO3 ceramics

Abstract This article reports the structural properties that influence the electrical and magnetic behaviours of polycrystalline Bi1−x Sm x FeO3 (x = 0, 0.1) ceramics. The samples are synthesized by a two-step solid state reaction. X-ray diffraction patterns expose two characteristic peaks corresponding to (104) and (110) planes around 31°. Bi1−x Sm x FeO3 (x = 0, 0.1) samples crystalize primarily in the R3c phase along with the traces of secondary phases. The Rietveld refinement analysis reveals that the tilt angle of Bi0.9Sm0.1FeO3 reduces due to the twisting of FeO6 octahedra compared to pristine BiFeO3. The electron density distribution and type of bonding are analyzed using the maximum entropy method. The microstructural analysis reveals that the Bi0.9Sm0.1FeO3 sample has a reduced average particle size compared to pristine BiFeO3. The influence of samarium ions in the bismuth site deviates the canting angle of the modulated spiral spin arrangement and the charge density distribution of the Bi0.9Sm0.1FeO3 sample as a result, the electrical and magnetic behaviours are improved compared with bare BiFeO3.

Influence of sintering temperature on the electrochemical properties of P2-type Na0.67Mn0.7Ni0.2Mg0.1O2 cathodes for sodium-ion batteries

Sodium-ion batteries are thought to be ideal alternatives to Lithium-ion batteries due to their similar electrochemical properties. However, several technique obstacles in cathode materials still impede the commercialized adoption of Sodium-ion batteries. Herein, the Mg-doping P2-type Na0.67Mn0.7Ni0.2Mg0.1O2 cathode materials were synthesized via a two-step process, including sol-gels and solid-state reaction method. This paper pays much attention to the optimal calcination temperature in the synthesis procedure and its effects are subsequently investigated. According to the results, under a series of calcination temperatures from 800 to 950 ​°C, Na0.67Mn0.7Ni0.2Mg0.1O2 cathode materials shows different particle sizes and crystalline structures, exhibiting varied electrochemical properties. Among them, samples calcinated at 900 ​°C display a high specific discharge capacity of 120.9 ​mAh g−1, and a stable cycling performance of 67.2% retention at 1 C rate for 100 cycles. The results suggest that calcination temperature at approximately 900 ​°C could effectively promote the electrochemical performance, which provides a good reference for the synthesis of cathode materials in sodium-ion batteries.

Effect of Ni and Fe substitution on the thermal, structural, vibrational spectroscopic and electrochemical properties of LiMn2O4 cathode material

Spinel LiMn2O4, Li1.025(Mn1.95Ni0.025Fe0.025)O4, and Li1.025(Mn1.9Ni0.025Fe0.05)O4 cathodes were synthesized by a two-step solid-state reaction method. The thermal, structural, vibrational spectra and electrochemical properties of these materials were characterized by using TGA-DTA, XRD, SEM, EDS, Fourier-FT-IR spectroscopy, Raman spectroscopy, and charge-discharge test. The TGA-DTA analysis confirmed that 800°C is the suitable temperature for synthesizing all the samples using Li2CO3, Fe2O3, MnO2, and NiO precursors. The XRD analysis revealed the formation of a single-phase cubic spinel structure with Fd3¯m space group. Two distinct strong absorption peaks were identified by FT-IR analysis in the wavenumber regions of 512 to 621 cm−1. Enhancement of the discharge specific capacity due to Ni and Fe substitution into LiMn2O4 was observed. Among all samples, Li1.025(Mn1.95Ni0.025Fe0.025)O4 exhibited excellent cyclic performance (97.4%) after 50 cycles.

Designing lead-free Barium Strontium Titanate-based weakly coupled relaxor ferroelectric ceramics with simultaneous high energy density and efficiency via Bi3+ lone pair covalent effect

Barium Strontium Titanate (Ba1-xSrxTiO3, BST) possesses the advantages of high permittivity, low remnant polarization and dielectric loss, suggesting great potential in the application of power capacitors. However, the low maximum polarization severely restricts the achievement of outstanding energy storage properties (ESP). Herein, we design a lead-free bulk ceramic: (1-x)Ba0.55Sr0·45TiO3-xBi0.5Na0.5TiO3 [(1-x)BST-xBNT] (x = 0.1–0.4), prepared by two-step solid-state reaction method. The introduction of BNT contributes to (1) the boost of maximum polarization (from 21 μC/cm2 up to 32.6 μC/cm2) due to Bi3+ lone pair covalent effect (2) strong relaxor behavior (1.71≪γ1.84) derived from weakly coupled nanopolar regions, which can be verified by high activation energy Ea = 0.341 eV at x = 0.3, improves the ESP and thermal stability of the ceramics. According to the above strategies, high Wrec = 1.73 J/cm3 and η = 84.4% are achieved in the 0.7BST-0.3BNT ceramics at 206 kV/cm, which is preferable to the previous results regarding BST-based bulk ceramics. The excellent thermal stability (20–120 °C), frequency stability (1–500 Hz), as well as anti-fatigue characteristic (cycling number: 105) were obtained in the 0.7BST-0.3BNT. Furthermore, 0.7BST-0.3BNT ceramics exhibit high-power density (PD = 44.9 MW/cm3) and rapid discharge rate (t0.9 = 99.2 ns) from 20 °C to 120 °C. This work provides a feasible way to achieve good energy storage and charge-discharge properties for pulse power energy storage systems.

MgPd2Sb : A Mg-based Heusler-type superconductor

We report the synthesis and physical properties of a full Heusler compound, MgPd$_2$Sb, which we found to show superconductivity below $T_c$ = 2.2 K. MgPd$_2$Sb was obtained by a two-step solid-state reaction method and its purity and cubic crystal structure (Fm-3m, a=6.4523(1) \r{A}) were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The results show that MgPd$_2$Sb is a type-II, weak coupling superconductor ($\lambda_{e-p}$ = 0.53). The observed pressure dependence of $T_c$ ($\Delta T_c / p \approx $ -0.23 K/GPa) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons, and electron-phonon coupling in MgPd$_2$Sb were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters tothose of all reported Heusler-type superconductors.

Synthesis, Luminescent Properties and White LED Fabrication of Sm3+ Doped Lu2WMoO9

In this paper, Sm3+ doped Lu2W0.5Mo0.5O6, Lu2WMoO9, and Lu2(W0.5Mo0.5O4)3 materials were synthesized by using a two-step solid-state reaction method. The synthesized materials were characterized by X-ray diffraction (XRD) patterns, field emission scanning electronic micrograph (FE-SEM) pictures, photoluminescence (PL) excitation and emission spectra, and temperature-dependent emission intensities. Orange-reddish light could be observed from the phosphors under ultraviolet (UV) 365 nm light. The Sm3+ doped Lu2WMoO9 had enhanced PL intensities compared to the other two materials. The excitation, the energy transfer, the nonradiative relaxation, and the emission processes were illustrated by using schematic diagrams of Sm3+ in Lu2MoWO9. The optimal Sm3+ doping concentration was explored in the enhancing luminescence of Lu2WMoO9. By combing the Sm3+ doped Lu2WMoO9 to UV 365 nm chips, near white lighting emitting diode (W-LED) were obtained. The phosphor can be used in single phosphor-based UV W-LEDs.

Effects of Sb2O3 on the microstructure and electrical properties of ZnO–Bi2O3-based varistor ceramics fabricated by two-step solid-state reaction route

In this work, the ZnO–Bi2O3–Cr2O3–Co2O3–MnO2 varistors doped with different content of Sb2O3 were prepared by two-step solid-state reaction route, including a pre-calcining of the mixtures of nanosized ZnO and the other additives at an optimized temperature, followed by a consequent sintering process at different temperatures. Meanwhile, the effects of Sb2O3 on the sintering temperature, microstructure and electrical properties of the objective varistors were investigated. It was found the densification temperature went up in a proper range and the content of pyrochlore phase, spinel phase and β-Bi2O3 phase increased with the increasing content of Sb2O3, while the grain size of ZnO–Bi2O3-based varistor reduced. The results demonstrated that at the same sintering temperature, the second particles increased with the increasing amount of Sb2O3, which was helpful to control the grain growth, leading to a higher breakdown voltage. However, the decrease of α-Bi2O3 phase (melting point of α-Bi2O3 phase is 825 °C), which is the main component of the liquid Bi2O3 phase in the sample during sintering process, leads to the increase of the sintering temperature of the green pallet. As a result, the ZnO varistor doped with 3.0 mol% Sb2O3 sintered at 1000 °C exhibited the highest breakdown voltage of 1863.3 V/mm. By contrast, the ZnO varistor without Sb2O3 doping sintered at 900 °C had the optimum nonlinear coefficient of 59.8.

Effect of Magnesium Doping to Reduce the Charge Reservoir Layer in Cu0.5Tl0.5(Ba2−xMgx)Ca2Cu3Oy (x = 0, 0.15, 0.25, 0.35) Superconductors

The charge reservoir layer plays a crucial role in the charge transfer mechanism in high-temperature superconductors. The effect of reducing the thickness of the Cu0.5Tl0.5Ba2O4−δ charge reservoir by replacing Ba with Mg atom in Cu0.5Tl0.5-1223 crystal has been studied. Cu0.5Tl0.5(Ba2−xMgx)Ca2Cu3Oy (x = 0, 0.15, 0.25, 0.35) superconductor samples were synthesized by a two-step solid-state reaction method. The as-grown samples showed orthorhombic crystal structure in which the c-axis lattice parameter and unit cell volume were systematically suppressed with increasing incorporation of Mg into the final compound, thereby resulting in suppression of the charge reservoir. The room-temperature resistivity increased with the Mg doping content, while the Tc and Tc-onset values decreased according to both resistivity and alternating-current (AC) susceptibility measurements. Fourier-transform infrared (FTIR) absorption measurements revealed three phonon modes related to vibrations of Tl–OA–Cu(2), Cu(1)–OA–Cu(2), and CuO2 planar oxygen atoms at around 420 cm−1, 480 cm−1 to 540 cm−1, and 580 cm−1, respectively. The apical oxygen mode of Tl–OA–Cu(2) type was hardened whereas the position of the latter two modes remained unchanged with increasing Mg doping in the final compound. Excess conductivity analyses showed a significant decrease in the onset temperature for Cooper pair formation (T*2D−SW). The coherence along the c-axis ξc(0), the interlayer coupling J, and the Fermi velocity vF of superconducting carriers increased with increasing Mg doping at Ba sites. These result suggest that the transfer mechanism of charge carriers from the Cu0.5Tl0.5Ba2O4−δ charge reservoir layer to the conducting CuO2 planes became more efficient, as evidenced by the increased coherence length ξc(0) and Fermi velocity vF of the carriers. However, the suppression of parameters such as Bc0(T), Bc1(T), Jc0(0), and τφ indicates that the density of pinning centers was suppressed with increasing Mg doping in the final compound.