Temperature Solid-state Reaction Research Articles

Cationic order-related magnetoresistivity and half-metallicity in bulk Pb2FeMoO6 grown by high pressure synthesis

We investigate the electric properties of Pb2FeMoO6 (PFMO), a double perovskite that can be grown in a bulk pure phase only via High Pressure/High Temperature solid-state reaction. The as-obtained PFMO is characterized by a high degree of cationic ordering at the B site between Fe3+ and Mo5+ and a ferrimagnetic transition with TN around 275 K. A semi-metallic to half-metallic transition seems to occur when the ferrimagnetic order arises thanks to the localization of a minority fraction of electrons on the Mo site. In this thermal regime, the system displays asymmetric magneto-resistivity, with selective-polarized carriers promoted by intense negative magnetic fields applied across the Néel transition during the cooling ramp. This cation-ordering related feature vanishes when the Mo-O bond length stabilizes, indicating a strong connection between the magnetic and electrical properties of this compound.

Design and fabrication of intermetallic NiCo electrocatalysts for the alkaline HER.

The design and fabrication of highly efficient electrocatalysts are crucial for reducing energy consumption, improving hydrogen production rates, and prolonging the service life of alkaline electrolyzers. In this study, intermetallic L10-NiCo electrocatalysts were designed using DFT calculations and fabricated through a one-step solid-state reaction method. The DFT calculations indicated that L10-NiCo presented a lower H adsorption Gibbs free energy and a moderate H2O dissociation barrier compared to the commonly used Ni catalyst and disordered NiCo alloy. Increasing the solid-state reaction temperature facilitated the formation of intermetallic L10-NiCo. Electrocatalytic tests for the alkaline HER demonstrated that the ECSA of L10-NiCo nanoparticles increased to 2.3 times, the overpotential decreased by 19%, the electrocatalytic activity increased to 1.5 times, and the stability improved to 2.2 times compared to those of the Ni nanoparticles. This research provides insights into the design and fabrication of highly efficient catalytic electrodes for alkaline electrolyzers.

Characteristics of Sodium Lithium Titanate Synthesized at Different Solid-State Reaction Temperature for Lithium-Ion Battery Anode

Characteristics of Sodium Lithium Titanate Synthesized at Different Solid-State Reaction Temperature for Lithium-Ion Battery Anode

A simplified and facile preparation method for the [Ca24Al28O64]4+(e-)4 electride.

Wide application of novel materials often requires low-cost preparation methods. In this study, we present a simplified and facile preparation method for the [Ca24Al28O64]4+(e-)4 electride material (C12A7:e-). Successful preparation of the C12A7:e- electride was confirmed by XRD patterns and magnetic behavior analysis. The concentration of electrons in the prepared C12A7:e- powder was calculated to be approximately 2.23 × 1021 cm-3, as evaluated by iodometry and TPD. DFT calculations provided insight into the unique electronic structure of C12A7:e-. Additionally, the substitution of the Ca reductant with CaH2 led to a reduction in the solid-state reaction temperature from 1100 to 950 °C, which can be attributed to thermodynamic effects such as a reduction in ΔG°.

How Halide Sub-Lattice Affects Li Ion Transport in Antiperovskites

Li-based antiperovskites (LiAP, Li3-x OH x X, X = Cl, Br) are an emergent class of Li-ion conductors that are potential candidates for electrolytes in all-solid-state batteries. As a material class, pLiAP shows vast compositional design freedom; however, the resulting properties are susceptible to synthesis and processing methodologies. For example, proton incorporation and halide mixing stabilize the perovskite cubic phase near room temperature, and halides mixtures near the eutectic points drive the solid-state reaction temperature down, allowing for faster synthesis and processing conditions (< 1 h). The mixed halogen compositions, such as Li2OHCl0.37Br0.63, also show a 30-fold improvement in room temperature ionic conductivity of a single halide structure, 1.5 x 10-6 vs. 4.9 x 10-8 S cm-1 (Li2OHCl). Despite the growing interest in these materials, important questions remain about LiAPs on the structure-property correlation upon halide substitution and the correlations between the OH/halide dynamics and the Li-ion transport. We thus attempted to deconvolute how proton dynamics and halide substitution enhance or impede ionic conduction in pLiAP at compositions near the halide salts' eutectic points.We combined infrared spectroscopy and nuclear magnetic resonance (NMR) with first-principles density functional theory (DFT) calculations to deconvolute halide mixing effects from local proton dynamics on Li-ion transport. The NMR results and ab initio molecular dynamics suggest that Li+ transport is more strongly correlated with halide dynamics. While the hydroxide does stabilize the highly conductive cubic structure, it limits correlative ionic transport and thus lowers Li+ conductivity.Experiment design, data analysis, and manuscript preparation (RLS) were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. Synthesis (THB and JN) were supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program. P. J. acknowledges partial support by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-96ER45579. H. F. was supported from U.S. Department of Energy (Award No. DE-EE0008865). This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The NMR characterization part of the work is supported by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, and Basic Energy Sciences. The NMR work was performed at the W. R. Wiley Environmental Molecular Sciences Laboratory, a DOE User Facility sponsored by the Office of Biological and Environmental Research, located at Pacific Northwest National Laboratory. Figure 1

Preparation of α-cordierite through mechanochemical activation of MgO–Al2O3–SiO2 ternary system

Samples of the ternary system MgO–Al2O3–SiO2 with stoichiometric composition in relation to α-cordierite (Mg2Al4Si5O18), consisting of 22.2 mol% MgO, 22.2 mol% Al2O3, and 55.6 mol% SiO2, were activated in a low energy mill with a constant speed of 100 rpm, in an aqueous medium. The precursors used were corundum (Al2O3), silica gel HF254 type 60 (SiO2), and periclase (MgO). The objective of the present study was to evaluate the effect of mechanochemical activation on the solid-state synthesis of α-cordierite, using a low energy ball mill. Another objective was to shed light on the effect of mechanochemical activation on the steps of α-cordierite formation. For this end several grinding conditions were evaluated, varying the time and mass ratio of precursors/grinding elements, as well as calcination at different temperatures between 950 °C and 1350 °C for 2 h. The samples were analyzed for the determination of the formed phases by Infrared (IR) and X-ray Diffraction (XRD). The phases identified in uncalcined samples were brucite (Mg(OH)2), forsterite (Mg2SiO4), enstatite (MgSiO3), spinel (MgAl2O3), amorphous silica (SiO2), corundum (α-Al2O3), and zirconia (monoclinic and tetragonal ZrO2). The lowest temperature corresponding to the formation of α-cordierite (α-Mg2Al4Si5O18) was 1150 °C and a considerable amount of this phase (16.2%) was observed at this temperature, for the sample with the higher mechanochemical activation. In a solid-state reaction, α-cordierite is normally obtained at around 1400 °C, therefore, the formation of this phase at 1150 °C confirms that the mechanochemical activation method, using a low-cost ball mill, is efficient in reducing the solid-state reaction temperature.

NaYTe2O7: A new compound with mixed valence of tellurium and large birefringence

A new compound with mixed valence of tellurium, namely, NaYTe2O7 has been successfully synthesized by the high−temperature solid state reaction through adopting substitution strategy. This compound crystallizes in the monoclinic space group of P21/n, and features two−dimensional [Te2O7]4− layer which is composed of TeVIO6 octahedra and TeIVO4 dispheniods. The anionic layers stack along [101] direction and interlinked by Y3+ and Na+ cations. The opposite arranged active lone pairs of TeIV and the layered anionic structure together induce the large birefringence which is estimated to be 0.18 at 1000 nm by first−principle calculation. This result indicates that the proper arrangement of lone pairs and directional covalent structure favor the increase of crystal’s birefringence. Furthermore, optical diffuse reflectance spectrum, infrared spectrum, thermal analysis and DFT calculations were also accomplished.

Improvement in the Crystallographic Phase Content and Superconducting Properties of Mechanically Alloyed MgB2

In this paper, the results of the superconductivity evaluation of MgB2 intermetallic-based superconducting materials prepared through mechanical alloying are reported. The formation of the MgB2 intermetallic phase took place through an intermediate phase reaction at the solid-state reaction temperature, which tends to favor single-phase materials. The annealing of mechanically milled Mg and B powders resulted in the highest mass fraction of MgB2 observed in this study, reaching more than 90% after annealing at 900 °C for 1 h. At that point, there were still second phases present consisting of Mg, MgO, and Fe2B. Improved superconducting properties were obtained in samples sintered at temperatures of 850 °C and 900 °C that had a low resistivity, low critical temperature gap values, and a high residual resistivity ratio (RRR).

Fabricating Uniform Tetragonal Barium Titanate Nanocrystals via Sand Milling Assisted by an Innovative Two-Step Calcination

Sand-milling machine was firstly utilized to crush and disperse the raw materials. A homogenous and well-dispersed mixture of TiO2 and BaCO3 (&lt;30nm) was obtained. The solid state reaction temperature can be reduced by 200°C for nanosized reactants compared with coarse ones. In order to increase tetragonality of nanosized BaTiO3, an innovative two-step calcination method, which includes solid state reaction process between reactants at a low temperature T1 and phase transition process at a high temperature T2, was subsequently adopted. The microstructure evolution of BaTiO3 by two-step calcination was investigated as a function of T2 and corresponding dwelling time t2. Pure-perovskite BaTiO3 nanopowders with the mean particle size as small as 75nm and tetragonality (c/a ratio) higher than 1.0096 could be fabricated by two-step calcination through altering T2 and/or its dwelling time t2.

Effects of solid-state reaction temperature on the activation energy and DC-bias superposition of NiCuZn ferrites based on master sintering curve

This work reports our recent studies on the microstructure and properties of NiCuZn ferrites, with particular interests in effects of solid-state reaction temperature on the sintering activation energy and DC-bias superposition characteristic. The theory of master sintering curve was used to investigate the densification evolutions of NiCuZn ferrites during sintering process. Experimental results demonstrated that materials with solid-state reaction temperature of 850°C exhibited the lowest value of activation energy, 577.6 kJ mol−1. When the solid-state reaction temperature was lower than 800°C, reaction could not be perfectly completed, which would hinder the consolidation process during heating up. In addition, increased solid-state reaction temperature could facilitate the homogeneous grain growth, reduce the final grain size and improve DC-bias superposition characteristic. Possible mechanisms behind are discussed.

Molten salt synthesis of Zn1.8Mn0.2SiO4 luminescent materials in NaCl–ZnCl2 eutectic salt

A low-temperature molten salt method has been used to synthesis Zn2SiO4:Mn (ZSM) powders in NaCl–ZnCl2 eutectic salts by using calcined SBA-15 as silica source without any post-treatment. Characterizations of the samples were carried out by X-ray diffraction, high resolution selection electron microscopy, Raman Spectroscopy and Photoluminescence. Our study revealed that the well crystalline ZSM was obtained at 450°C, much lower than the conventional solid-state reaction temperature but also get better crystallinity when the temperature increased to 500°C. The SEM micrographs of ZSM are comprised of irregular rod-like structure with different length–diameter ratio, which showed the average length is about 1μm and the average diameter is around 100nm. Besides, the UV excitation spectra showed that the ZSM phosphor exhibited a strong green emission around 527nm and reached the highest luminescence intensity with the Mn doping concentration of 0.2. In addition, the luminescence decay time of Zn1.8Mn0.2SiO4 (x=0.2) around 527nm lasted for 14.25ms upon 245nm excitation.

Solid-state synthesis of Li4Ti5O12 whiskers from TiO2-B

In this work, Li4Ti5O12 (LTO) was synthesized from the precursors of TiO2-B and anatase whiskers, respectively. The synthesized LTO whiskers from TiO2-B whiskers via a solid state reaction at 650°C have a high degree of crystallinity with an average diameter of 300nm. However, when anatase whiskers were used as the precursor, only particle morphology LTO was produced at 750°C. The further analysis of the precursors, the intermediate products and the final products reveal that the crystal structure of the anatase hinders the diffusion of lithium, leading to a typical reaction–diffusion process. Under this condition, only particle morphology LTO can be produced. However, the crystal structure of the TiO2-B is easy for lithium diffusion and the process is performed in two separated steps (i.e., diffusion and reaction), which makes it possible to decrease the solid-state reaction temperature down to 650°C and then maintain the morphologies of whiskers.

Effect of solid-state reaction temperature on electrochemical performance of LiMn2O4 submicro-rods as cathode material for Li-ion battery by using γ-MnOOH submicro-rods as self-template

LiMn2O4 submicro-rods are synthesized via solid-state reaction by using γ-MnOOH submicro-rods as self-template, which is prepared via a solvothermal process in the presence of ethanol/water solvent by using KMnO4 and MnCl2 as raw materials. It is found that the ethanol content in a certain ethanol/water volume ratio range has no obvious influence on the crystal phase and morphology of γ-MnOOH submicro-rods derived from the solvothermal process, and a proper solid-state reaction temperature range for the preparation of spinel LiMn2O4 submicro-rods by using γ-MnOOH submicro-rods as self-template is 500∼700°C. Moreover, the effects of reaction temperature on structure, crystal phase and electrochemical performance of the obtained LiMn2O4 submicro-rods as cathode material of Li-ion battery are studied in detail, and the LiMn2O4 submicro-rods obtained at 600°C exhibit the best electrochemical performance with an initial capacity of 125.6 mAh g−1 and 95.6% capacity retention after 100 cycles at 3C. Importantly, the rod-like nanostructure and crystal phase can be well preserved after prolonged the charge/discharge cycling time at a relatively high current rate, indicating its good structural stability as cathode material. Further development of this γ-MnOOH submicro-rod self-templating method may be interesting for the commercial production of LiMn2O4 for Li-ion batteries with superior high-rate capability and good cycling stability.

Ordered LiNi0.5Mn1.5O4 hollow microspheres as high-rate 5 V cathode materials for lithium ion batteries

Ordered LiNi0.5Mn1.5O4 hollow microspheres have been synthesized by an impregnation method followed by a simple solid-state reaction, and their electrochemical performance is investigated as cathode material for lithium ion batteries. The morphologies of the LiNi0.5Mn1.5O4 products prepared at different temperatures reveal that the formation for the hollow structure is tightly relative to the temperature for the solid-state reaction. Then ordered LiNi0.5Mn1.5O4 hollow microspheres are formed under the solid-state reaction temperature of 800°C along with post-annealing at 700°C, but the sample prepared without post-annealing exists at the form of disordered structure. When the ordered LiNi0.5Mn1.5O4 hollow microspheres were applied as the cathode materials for lithium ion batteries, they exhibited superior rate capability (116 mAh g−1 at 5C, 85 mAh g−1 at 10C for charge and discharge) and good cyclability, which are much better than the disordered sample. The durable high-rate capability was attributed to their single-crystal surface configuration that benefits fast Li insertion/extraction kinetics.

Correlation between processing conditions, microstructure and charge transport in half-Heusler alloys

Abstract Five bulk samples of n-type Zr 0.25 Hf 0.75 NiSn 0.975 Sb 0.025 half-Heusler (HH) alloy were fabricated by reacting elemental powders via (1) high temperature solid state (SS) reaction and (2) mechanical alloying (MA), followed by densification using spark plasma sintering (SPS) and/or hot pressing (HP). A portion of the sample obtained by SS reaction was mechanically alloyed before consolidation by hot pressing (SS–MA–HP). X-ray powder diffraction and transmission electron microscopy studies revealed that all SS specimen (SS–SPS, SS–HP, SS–MA–HP) are single phase HH alloys, whereas the MA sample (MA–SPS) contains metallic nanoprecipitates. Electronic and thermal transport measurements showed that the embedded nanoprecipitates induce a drastic increase in the carrier concentration ( n ), a large decrease in the Seebeck coefficient (S) and a marginal decrease in the lattice thermal conductivity ( κ l ) of the MA–SPS sample leading to lower ZT values when compared to the SS–HP samples. Constant values of S are observed for the SS series regardless of the processing method. However, a strong dependence of the carrier mobility ( μ ), electrical conductivity ( σ ) and κ l on the processing and consolidation method is observed. For instance, mechanical alloying introduces additional structural defects which enhance electron and phonon scattering leading to moderately low values of μ and large reduction in κ l . This results in a net 20% enhancement in the figure of merit (ZT=0.6 at 775 K). HH specimen of the same nominal composition with higher ZT is anticipated from a combination of SS reaction, MA and SPS (SS–MA–SPS).

Preparation and Optimization of Long Persistent Luminescent Sr&lt;SUB&gt;4&lt;/SUB&gt;Al&lt;SUB&gt;14&lt;/SUB&gt;O&lt;SUB&gt;25&lt;/SUB&gt;:(Eu,Dy) Phosphor Materials

Sr4Al14O25:(Eu,Dy) phosphor materials were prepared by solid state reaction. The dependence of long per- sistent luminescence from Sr4Al14O25:(Eu 2+ , Dy 3+ ) on the amounts of H3BO3, the solid state reaction temperature, and the contents of Eu were studied. It was found that the addition of H3BO3 as the flux agent was critical for the formation of the blue-green emitting Sr4Al14O25 phase. Sr4Al14O25 phosphors with persistent luminescence of 490 nm and after- glow time more than 24 h was obtained for the sample prepared at 1400℃ with the doping amounts of H3BO3 of 10at% and Eu/Al atomic ratio of 0.03, respectively. Furthermore, the dependence of persistent luminescence intensity on Eu content indicates that the persistent luminescence process is mainly controlled by the electron transition rate from deep traps to Eu 2+ levels.

Structure and luminescence properties of Mn-doped Zn 2SiO 4 prepared with extracted mesoporous silica

Zn 2SiO 4:Mn powders were prepared by solid-state reaction using extracted SBA-15 as silica source. The well crystalline willemite Zn 2SiO 4:Mn can be obtained at 800 °C, much lower than the conventional solid-state reaction temperature and lower than using the calcined SBA-15. This can be attributed to the high reactive activity of the extracted SBA-15 due to its high density silanol groups, large surface areas, and non-crystalline structure. Ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectra reveal the host lattice absorption band around 162 nm and the charge transfer transition band around 245 nm. The Zn 2SiO 4:Mn phosphor exhibits a strong green emission around 527 nm. The Zn 2SiO 4:Mn phosphor with an Mn doping concentration of 0.06, i.e., Zn 1.94Mn 0.06SiO 4, shows the highest relative emission intensity. Upon 147 nm excitation, the luminescence decay time of the green emission of Zn 1.94Mn 0.06SiO 4 around 527 nm is 8.87 ms.

Optical properties of SnO2 nanoparticles

In recent times, considerable research efforts have been focused on the exploration of novel optical properties of nanocrystalline SnO2 particles such as photoluminescence (PL). In the present work, spherical SnO2 nanoparticles are synthesized by solid state reaction at different temperatures using tin chloride dihydrate and sodium hydroxide flakes as precursors. Transmission electron micrograph shows uniform and spherical SnO2 nanoparticles of diameter 30–40 nm. Micro-Raman spectra show an inverse relationship of line-width with SnO2 particle size. The band gap of SnO2 is calculated by plotting (αhν)2vs. hν and extrapolating the linear portion of it to α = 0 and found it to be 3.76–4.24 eV. Photoluminescence intensity increases with the increase of solid state reaction temperature up to 873 K. This is attributed to the generation of the oxygen ion vacancies in SnO2.

Comparison of Characteristics of Gd2BaCuO5 Powders Prepared by Different Processes

Abstract Ultra-fine Gd 2 BaCuO 5 (Gd211) powders were prepared by three different routes including low temperature combustion synthesis (LCS), coprecipitation and solid state reaction. The powders were characterized in terms of morphology, chemical purity, specific surface area and particle size. The results show that LCS process yields the most weakly agglomerated powder with smallest average particle size. The microstructure and superconductor property of GdBa 2 Cu 3 O 5 (Gd123) bulk material fabricated from the precursor of Gd211 powders were also studied. It is found that the employment of fine Gd211 starting powder is effective for the size reduction of Gd211 particles in the bulk samples. Gd123 bulk produced from LCS powder achieved the largest critical current density ( J c ) value compared with those from other two powders.

Multitwinned Spinel Nanowires by Assembly of Nanobricks via Oriented Attachment: A Case Study of Zn2TiO4

Nanowires with twinned morphology have been observed in many cubic-phase materials including spinel. We study systematically the formation of multitwinned Zn(2)TiO(4) nanowires based on a solid-solid reaction of ZnO nanowires with a conformal shell of TiO(2), which is deposited by atomic layer deposition (ALD). By varying the solid-state reaction temperature, reaction time, and TiO(2) shell thickness, the formation process is carefully analyzed with the help of transmission electron microscopy. It is found that the multitwins develop through an oriented attachment of initially separated spinel nanobricks and a simultaneous Ostwald ripening process. The oriented assembly of the individual bricks is strongly dependent on annealing conditions, which is required to favor the motion and interaction of the bricks. This mechanism differs dramatically from those proposed for twinned nanowires grown with the presence of metal catalysts. Our result provides new insights on controlling the morphology and crystallinity of designed 1-D nanostructures based on a solid-state reaction route.