Two-step Solid-state Reaction Research Articles

Electrical properties of 0.94Bi0.5Na0.5TiO3–0.06Ba(Zr0.055Ti0.945)O3 lead-free ceramics with high thermal stability

Here we report the 0.94(Bi0.5Na0.5)TiO3–0.06Ba(Zr0.055Ti0.945)O3 (0.94BNT–0.06BZT) lead-free ceramics was synthesized by two-step solid state reaction route. The structural, dielectric, ferroelectric, piezoelectric and electromechanical properties of the ceramics were studied, and showed excellent electric properties (P s = 39.9 μC/cm2, P r = 33.7 μC/cm2, E c = 2.79 kV/mm, S = 0.20%, d 33 = 174 pC/N, k p = 0.33). The depolarization temperature (T d ) of the ceramics is about 65 °C, which is determined from the first hump of relative dielectric constant. The electromechanical factor k p disappears at 65 °C, is consistent with the depolarization temperature (T d ) and the ferroelectric-antiferroelectric phase transition temperature (T fe−afe ) determined from the temperature-dependent P–E and bipolar S–E curves. These results indicate the 0.94BNT–0.06BZT ceramics has a good thermal stability in range of − 60–60 °C, and meets the actual demand.

Effects of (Bi0.5Na0.5)ZrO3 addition on relaxation behavior and electrical properties of the KNN–LS ceramics

[0.94K0.48Na0.52Nb–(0.06−x)LiSbO3–xBi0.5Na0.5ZrO3, x = 0, 0.01, 0.02, 0.03, 0.04, 0.05] lead-free piezoelectric ceramics were prepared by a traditional two-step solid-state reaction method. The effects of BNZ addition on phase structure, electrical properties and dielectric relaxation of KNN–LS ceramics were investigated in this paper. X-ray diffraction patterns exhibit that the ceramics have a homogeneous perovskite structure with no other phases. (Bi0.5Na0.5)ZrO3 doping can promote grain growth, increase density and enhance the electrical properties of the KNN–LS ceramics. When the addition amount (x) of BNZ is 0.04 mol, the ceramic exhibits optimum electrical properties: d33 = 286pC/N, Kp = 42%, er = 2400, tanδ = 0.044. The dielectric constant and diffusive phase coefficient of the ceramics increase with the increase of BNZ. This indicates that the ceramics are with excellent relaxation behavior. When x is 0.01 mol, the dispersion coefficient γ reaches the maximum (1.55605) and the curie temperature of the ceramics is up to 350 °C. These results confirm that the ceramics are with the potentialities to be applied in the high temperature lead-free relaxor ferroelectrics.

LiFeP: A new anode material for lithium ion batteries

Transition metal phosphides are promising anode materials for lithium ion batteries because of their abundant natural resources and high theoretical capacities. In this study, the electrochemical properties of LiFeP as an anode material for lithium ion battery were investigated for the first time. LiFeP powders were successfully synthesized by a conventional two-step solid-state reaction method. The results of X-ray powder diffraction and selected area electron diffraction revealed that the layered plate-like LiFeP was stacked by the (001) crystal plane. As an electrode material, LiFeP delivered a superior reversible capacity of 507 mA h g−1 at a high current density of 300 mA g−1 after 300 cycles and excellent rate performance. After cycling, the layered structure can be well maintained, which would be greatly beneficial to the electrochemical performance of LiFeP. The reason for the increase in capacity was also investigated and can be attributed to the high number of conversion reactions of LiFeP and the generation of elemental P during cycling.

Facile synthesis and systematic study of Eu2+ doped SrSi2O2N2 green-emitting phosphor based on a new method

Eu2+ doped SrSi2O2N2 green-emitting phosphors were successfully synthesized via two-step and one-step solid-state reaction method, respectively. Their crystalline structure, luminescence properties and morphologies were experimentally investigated in comparison. In particular, SrSi2O2N2:Eu2+ phosphors have an efficient green emission band that peaks at 540nm. A red shift tuning capability of emission bands was achieved by increasing the Eu2+ contents. Investigation on the thermal quenching effect suggested concentration quenching effect for Eu2+ and good thermal stability. By thoroughly comparative study, two-step method is superior to one-step method, in the aspects of elimination of interphase, thermal stability, crystal size and luminescence.

Ni Nanoparticle-Added Ni x /(Cu 0 . 5 Tl 0 . 5 )Ba2Ca2Cu3 O 10-δ Superconductor Composites and Their Enhanced Flux Pinning Characteristics

Ni nanoparticle-added Ni x /(Cu0.5Tl0.5)Ba2Ca2 Cu3 O 10-δ superconductor composites are synthesized at normal pressure by two-step solid-state reaction method. The idea for adding ferromagnetic nanoparticles was to create artificial pinning centers at grain boundaries. The samples have shown orthorhombic crystal structure in which the cell parameters increase with an increase in the added concentration of Ni nanoparticles. This shows that due to the higher reactivity, Ni nanoparticles partially diffuse into the unit cell of (Cu0.5Tl0.5)Ba2Ca2Cu3 O 10-δ superconductors. This also indicates as an evidence of the occupancy of these nanoparticles at grain boundaries. A metallic variation of resistivity from room temperature down to the onset of superconductivity is a typical feature of these samples with T c (R = 0) varying between 92 and 94 K. The magnitude of diamagnetism is significantly enhanced in 7 and 10% nanoparticle-added samples. The enhanced magnetization of ferromagnetic nanoparticles at reduced temperature plays a vital role in reducing the diamagnetism of nanosuperconductor composites. The softening of apical oxygen modes of type Cu(1)–OA–Cu(2) has confirmed the diffusion of Ni nanoparticles into the unit cell of the final compound. The excess conductivity analyses of conductivity data have shown that the values of B c (0), B c1, and J c are enhanced with the addition of Ni nanoparticles in the final compound. Variation of superconducting properties was attributed to pair breaking due to spin scattering across these ferromagnetic Ni nanoparticles. This shows that added Ni nanoparticles act as efficient pinning centers, which is also confirmed by the suppression of the London penetration depth.

BiS2-based superconductor presents ductile-like tribo-mechanical behavior

Adequate mechanical responses are decisive features for novel superconductor materials, ideally enabling their machinability and conformability capacities to produce practical devices. The recently developed polycrystalline Bi4O4S3 superconductor was prepared following a two-step solid state reaction. Grains consisted of lamellae, ∼5 μm in the planar orientation and 100–500 nm thick, presenting a tetragonal crystalline structure. The mechanical and tribological properties of the millimeter-size samples were investigated at the nanoscale using varied testing routines. Indentation hardness was about 1.6 GPa, whereas elastic modulus was 50–53 GPa. At the nanometer scale, cracks were visible through all the surface, possibly due to the structural inherent features of the material. On the other hand, it disclosed ductile-like plastic deformation features under normal loading and scratch tests up to 100 mN, as predicted by the index of plasticity H/E* ≈ 0.3. In these tests, the BiS2-based material presented some limited strain hardening, but with the absence of load-induced fractures.

The impact of anion ordering on octahedra distortion and phase transitions in SrTaO2N and BaTaO2N.

In this work we synthesized BaTaO2N and SrTaO2N using a two-step high-temperature solid-state reaction method and analysed the structural distortions, relative to the ideal cubic perovskite structure, according to group theory. From a complete distortion analysis/refinement using high-resolution neutron diffraction data in the temperature range 8 to 613 K, we identified tetragonal structures for BaTaO2N [P4/mmm (No. 123)] and SrTaO2N [I4/mcm (No. 140)]. In contrast to an anion-disordered cubic perovskite (Pm \overline{3}m No. 221) with Ta at the cell center, both systems show a site preference for oxygen anions in the two opposite corners (along the c axis) of the Ta-O/N octahedra rather than the four square corners in the ab plane (Γ3+ occupancy distortion), which induces a tetragonal elongation of the unit cell with the c axis being longer than the a axis. A further Ta-O/N octahedra displacement [R5-(a,0,0), rotation about the c axis] distortion was observed in SrTaO2N. This distortion mode is accompanied by an increased unit-cell distortion that decreases as the temperature increases. Ultimately a second-order phase transition caused by the loss of the R5-(a,0,0) mode was observed at 400-450 K.

Enhanced Thermoelectric Properties in BiCuSeO Oxyselenides via Zn and S Dual-Site Substitution

We report on the effect of Zn and S dual-site substitution on the thermoelectric properties of Bi1−x Zn x CuSeO1−x S x (x = 0, 0.025, 0.05, 0.075) oxyselenides prepared by conventional two-step solid-state reaction followed by inductive hot-pressing sintering. BiCuSeO phase with lath-like microstructures was observed for all samples. Upon Zn and S dual-site substitution, the electrical conductivity at 750 K was improved from 28.9 S cm−1 for pure BiCuSeO to 43.3 S cm−1 for Bi0.975Zn0.025CuSeO0.975S0.025 with highest Seebeck coefficient of 360 μV K−1 for Bi0.95Zn0.05CuSeO0.95S0.05. A maximum power factor of 4.6 μW cm−1 K−2 was achieved for Bi0.95Zn0.05CuSeO0.95S0.05 at 750 K due to its moderate electrical conductivity and high Seebeck coefficient. As the enhanced power factor compensates for the slight increase in the total thermal conductivity, the dimensionless figure of merit ZT reached a maximum value of 0.68 for Bi0.95Zn0.05CuSeO0.95S0.05 at 750 K, approximately 1.7 times larger than that of pristine BiCuSeO.

Green solid-state chemical synthesis and excellent xylene-detecting behaviors of Y-doped α-MoO3 nanoarrays

Y-doped α-MoO3 nanoarrays constructed by nanorods were simply synthesized by a facile and simple two-step solid-state chemical reaction. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy were applied to characterize the micro-structures and surface chemical composition of the as-prepared products. The results suggested that Y element had been successfully doped into the α-MoO3 nanoarrays. The gas-sensing behaviors of Y-doped nanoarrays toward seven kinds of harmful gases were also investigated. The results indicated that the Y-doped α-MoO3 nanoarrays display not only an improved response (the response value reaches 28.3 to 100ppm xylene), but also an excellent selectivity to xylene. The good xylene-detecting behaviors were attributed to smaller size and the relative larger surface area. Furthermore, the doping of Y increased the electron donor defects and oxygen vacancies, which accelerated the mobility of oxygen ions and enhanced the conductivity of material, resulting in enhanced response to xylene.

Preparation and characterization of LiFePO4·xLi3V2(PO4)3 composites by two-step solid-state reaction method for lithium-ion batteries

LiFePO4·xLi3V2(PO4)3 (LFP·xLVP, x=0, 0.05, 0.1, 0.15, 0.2) composites were prepared by the two-step solid-state method. The structure, morphology and electrochemical properties were characterized by X-ray diffraction, scanning electron microscope, cyclic voltammetry, charge-discharge performance test and electrochemical impedance spectroscopy. It was indicated that composites were presented rough in surface of ball-like particles. Two phase of LFP and LVP combination improved electrochemical properties of LFP. The LFP·0.1LVP has the highest discharge capacity of 154mAh/g at 0.2C. Compared with LFP, the rate performance of the LFP·0.1LVP increased 13% and 8% at 1C and 10C after five cycles. It possessed excellent cycle life of 99.8% after 100 cycles at 1C especially. The all preparation process without any solvent addition was easy operation, energy saving and environmentally friendly.

Understanding microwave dielectric properties of (1\u2212x)CaTiO3\u2013xLaAlO3 ceramics in terms of A/B-site ionic-parameters

We prepared (1−x)CaTiO3–xLaAlO3 (0 ≤ x ≤ 1) microwave dielectric ceramics using a conventional two-step solid-state reaction method, and investigated microwave dielectric properties of the ceramics in terms of A/B-site ionic-parameters. Ionic-parameters such as ionic polarizability, A-site bond valence, and ionic rattling were linked to the microwave dielectric properties. As the LaAlO3 content x in the (1−x)CaTiO3–xLaAlO3 ceramics increased from 0.3 to 0.7, the dielectric constant gradually decreased, which was attributed to the decrease of polarizability deviation and suppression of the cation rattling. The temperature coefficient of the resonant frequency decreased as the content of LaAlO3 increased because of the increase of A-site cation bond valence. The quality factor value (Q × f) increased as LaAlO3 content increased because of the enhancement of the order degree of B-site cation. A significant deterioration of the temperature coefficient of the resonant frequency and Q × f value was observed at the composition x = 0.5. These decreases were attributed to a phase transition from orthorhombic crystal (for x ≤ 0.5) to rhombohedral crystal (for x > 0.5).

P-type transparent LaCuOS semiconductor synthesized via a novel two-step solid state reaction and sulfurization process

A novel and simple two-step preparation method has been successfully developed to synthesize high quality oxychalcogenide LaCuOS, a direct-gap p-type transparent semiconductor. We first successfully synthesized CuLaO2 using cheap Cu2O and La2O3 via solid state reaction, and then achieved high quality LaCuOS through sulfurization at an optimum temperature of 860°C without using conventional hazardous H2S or CS2 gas. With the use of easily available and relatively more stable starting materials of Cu2O, La2O3 and S, this method is less costly than conventional solid state reaction route for obtaining oxychalcogenides. The synthesized LaCuOS of high purity has a band gap of 3.1eV and gives a resistivity of 0.25MΩcm and high seebeck coefficient of +515µV/K. Moreover, it demonstrates strong luminescence at room temperature. The success of this novel two-step synthesis method also opens a door for environmental friendly synthesis of other high performance oxychalcogenides.

Enhanced thermoelectric properties and electronic structures of p-type BiCu1−xAgxSeO ceramics

The thermoelectric properties and electronic structures were investigated on p-type BiCu1-xAgxSeO (x=0, 0.02, 0.05, 0.08) ceramics prepared using a two-step solid state reaction followed by inductively hot pressing. All the samples consist of single BiCuSeO phase with lamella structure and no preferential orientation exists in the crystallites. Upon replacing Cu+ by Ag+, maximum values of electrical conductivity of 36.6Scm−1 and Seebeck coefficient of 350μVK−1 are obtained in BiCu0.98Ag0.02SeO and BiCu0.92Ag0.08SeO, respectively. Nevertheless, a maximum power factor of 3.67μWcm−1K−2 is achieved for BiCu0.95Ag0.05SeO at 750K owing to the moderate electrical conductivity and Seebeck coefficient. Simultaneously, this oxyselenide exhibits a thermal conductivity as low as 0.38 Wm−1K−1 and a high ZT value of 0.72 at 750K, which is nearly 1.85 times as large as that of the pristine BiCuSeO. The enhancement of thermoelectric performance is mainly attributed to the increased density of states near the Fermi level as indicated by the calculated results.

A two-step solid-state reaction to synthesize the yellow persistent Gd3Al2Ga3O12:Ce3+ phosphor with an enhanced optical performance for AC-LEDs.

By using a two-step solid-state reaction to synthesize the yellow-persistent Gd3Al2Ga3O12:Ce3+ phosphor, both the luminescence and afterglow properties were greatly enhanced. Its internal quantum efficiency reaches as high as 81.9%, indicating its promising application in reducing the flicker effect in AC-LED-based white light systems.

Effect of Nd<sub>2</sub>O<sub>3</sub> on the Microwave Dielectric Properties of 0.67CaTiO<sub>3</sub>-0.33LaAlO<sub>3</sub> Ceramics

0.67CaTiO3-0.33LaAlO3 ceramics doped with Nd2O3 were prepared using a conventional two-step solid-state reaction, and the effect of Nd2O3 doping on the microwave dielectric properties were studied. A single phase of perovskite structure was confirmed with the Nd2O3 doping. The results showed that the addition of Nd2O3 obviously improved the density and Q×f values of CTLA ceramics. The dielectric constant were almost not affected and the τf values were close to zero with the increase of the doping amount. CTLA ceramics with 0.2 wt% Nd2O3 doping sintered at 1380 °C for 4 h exhibited the optimal microwave dielectric properties of εr = 45.36, Q×f = 37,890 GHz, τf = 7.80 ppm/°C.

Sintering Behavior and Microwave Dielectric Properties of Li<sub>2</sub>O-B<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Doped 0.67CaTiO<sub>3</sub>-0.33LaAlO<sub>3</sub> Ceramics

A low temperature sintering method was used to avoid the relatively high sintering temperatures typically required to prepare 0.67CaTiO3-0.33LaAlO3 (CTLA) ceramics. 0.67CaTiO3-0.33LaAlO3 ceramics doped with Li2O-B2O3-SiO2 (LBS) were prepared by a conventional two-step solid-state reaction process. The sintering behavior, crystal structure, surface morphology, and microwave dielectric proprieties of the prepared ceramics were studied. As the small amount of LBS content increased, the small amount of liquid phase formed in an amorphous state around the surface of the grain boundaries. With the increase the content of LBS glass, the quality factor (Q×f) value decreased. CTLA+0.05 wt.% LBS ceramics sintered at 1320°C for 4h exhibited the optimal microwave dielectric properties of dielectric permittivity (εr) = 45.02, quality factor (Q×f) = 37400 GHz, and temperature coefficient of resonant frequency (τf) = 9.84 ppm/°C. .

Effect of Mn-doping on the structure and electric properties of 0.64Pb(In0.5Nb0.5)O3-0.36PbTiO3 ceramics

In order to study the effect of defect dipoles on relaxor-based ferroelectrics, 0.64Pb(In0.5Nb0.5)O3-0.36Pb(Ti1−xMnx)O3 (x=0−0.15) ferroelectric ceramics were synthesized using the two-step solid state reaction method. The phase structure, ferroelectric, piezoelectric and dielectric properties were investigated. Upon increasing the Mn content, the phase of the ceramics transforms from tetragonal to rhombohedral symmetry, the magnitude of remnant polarization and piezoelectric coefficient decreasing because of the hardening effect of the defect dipoles and the variation of composition. The coercive field, however, decreases from 22kV/cm to 12.5kV/cm with x≤0.04 initially owing to a phase transition, and then increasing since the defect dipoles provided a driving and stabilizing force for domain stability. The stabilizing force also resulted in constricted hysteresis loops for samples with composition of x≥0.04 after aging. The temperature dependence of dielectric properties showed that the Curie temperature decreased from 312°C (x=0) to 237°C (x=0.15), and the degree of relaxor behavior was enhanced with increase of Mn content. It indicates that the defect dipoles, confirmed by the existence of oxygen vacancies, play an important role in the electrical properties of Mn-doping PIN-PT ceramics.

The Role of Mass of Doped Atoms in the Superconductivity of Cu0.5Tl0.5Ba2Ca2Cu3O10−d and Cu0.5Tl0.5Ba2Ca2Cu1.5 M1.5O10−d (M = Cd, Zn, and Ni)

For the investigation of any possible role of the mass of atoms in the mechanisms of higher T c superconductivity, we have synthesized Cu0.5Tl0.5Ba2Ca2Cu3O10−d and Cu0.5Tl0.5Ba2Ca2Cu1.5 M 1.5O10−d (M = Cd, Zn, and Ni) samples by two-step solid-state reaction method at 860°C. The synthesized samples have shown orthorhombic crystal structure, and the unit cell volume increases with the doping of M atoms. A suppression in the onset temperature of superconductivity and zero-resistivity critical temperature is observed with the doping of Cd; whereas, these parameters are enhanced with the doping of Ni and Zn. In FTIR absorption measurements, the apical oxygen mode of type Tl–OA–Cu(2) mode is hardened with the incorporation of M = Cd, Zn, and Ni atoms, confirming the doping of these elements in the final compound. In excess conductivity analyses, a suppression is observed in the values of coherence length ξ c (0), inter-layer coupling J and the Fermi velocity V F of carriers with the doping of Cd; whereas the values of these parameters are enhanced with Zn and Ni doping. However, Cd atoms have also been found to induce the enhancements of flux-pinning characters as B c0 (T), B c1 (T), and J c (0); whereas the values of these parameters are suppressed in Ni- and Zn-doped samples. A suppression of magnetic field penetration depth (λ p.d) and the Ginzburg-Landau (GL) parameter κ are observed in Cd-doped samples. The energy required to break apart the Cooper pairs is suppressed in the Cd-doped samples showing that Cd-doped samples promotes weak superconductivity These studies confirm that doped Cd atoms induce anharmonic oscillations in the solid-state medium which suppress the density of phonons and hence the density of Cooper pairs that stress the importance of electron-phonon interaction in the mechanism of high T c superconductivity.

Enhancing the performance of high-voltage LiCoMnO4 spinel electrodes by fluorination

Abstract With the aim of improving the electrochemical properties of the LiCoMnO4 high-voltage spinel for lithium ion battery applications, LiCoMnO4-yFy (y = 0, 0.05, 0.1) compounds were synthesized by a two-step solid-state reaction at 800 °C. The stoichiometry of the samples was verified by nuclear reaction analysis for the fluorine stoichiometry, inert gas fusion analysis for the oxygen stoichiometry, and inductively coupled plasma optical emission spectroscopy for the cation stoichiometry. X-ray diffraction analysis and scanning electron microscopy revealed increasing phase purity and changing microstructure upon fluorine incorporation. Electrochemical characterizations were carried out in battery test cells using a liquid electrolyte. The samples show poor coulombic efficiency, due to liquid electrolyte decomposition. However, fluorinated spinels demonstrated significantly improved capacities of up to 18% and improved cycling stability of up to 20%, compared to their non-fluorinated counterparts.

Synthesis and luminescence characterization of Y2 BaZnO5 :RE (RE=Eu3+ , Tb3+ , Pr3+ and Sm3+ ) phosphors.

Modified synthesis and luminescence of Y2 BaZnO5 phosphors activated with the rare earths (RE) Eu3+ , Tb3+ , Pr3+ and Sm3+ are reported. RE2 BaZnO5 phosphors have attracted attention because of their interesting magnetic and optical properties; and are usually prepared using a two-step solid-state reaction. In the first step, carbonates or similar precursors are thoroughly mixed and heated at 900°C to decompose them to oxides. To eliminate the unwanted phases like BaRE2 O4 , the resulting powders are reheated at 1100°C for a long time. We prepared Y2 BaZnO5 phosphors activated with various activators by replacing the first step with combustion synthesis. The photoluminescence results are presented. The photoluminescence results for Eu3+ , Tb3+ and Pr3+ are in good agreement with the literature. However, photoluminescence emission from Sm3+ has not been documented previously. The excitation spectrum of Eu3+ is dominated by a charge transfer band around 261nm, and an additional band around 238nm is always present, irrespective of the type of activator. The presence of this band for all these different types of activators was interpreted as host absorption.