Conventional Solid-state Synthesis Research Articles

Transport properties of highly dense proton-conducting BaSn1−xInxO3−δ ceramics

Doped barium stannate belongs to the perovskite-structured complex oxides with proton transport capability. Such objects are of high interest in terms of their application in various protonic ceramic electrochemical cells. In the present work, In-doped barium stannate (BaSn1−xInxO3−δ, 0 ≤ x ≤ 0.4) materials were prepared and thoroughly characterized by structural, microstructural, and electrochemical techniques. The single-phase and high-dense ceramic materials were prepared by the conventional solid-state synthesis route over the entire doping range investigated. The chemical composition of these materials was found to be in close agreement with the nominal values, indicating no evaporation of Ba-, Sn-, or In-containing phases during sintering. The high-temperature electrochemical analysis showed that the ionic conductivity of BaSn1−xInxO3−δ gradually increases with increasing the In-content without reaching a concentration maximum, even for high dopant concentrations. The relatively high activation energy values indicate that this ionic conductivity is determined by oxygen-ionic transport, which, however, becomes predominantly protonic at reduced temperatures. The determination of bulk and grain boundary transport showed that both were improved with the In-doping. The possible reasons for these observations were discussed in detail in this work. Therefore, the obtained data are important for discovering the transport properties of stannates and their potential applications.

Unveiling Crucial Chemical Processing Parameters Influencing the Performance of Solution-Processed Inorganic Thermoelectric Materials.

Production of thermoelectric materials from solution-processed particles involves the synthesis of particles, their purification and densification into pelletized material. Chemical changes that occur during each one of these steps render them performance determining. Particularly the purification steps, bypassed in conventional solid-state synthesis, are the cause for large discrepancies among similar solution-processed materials. In present work, the investigation focuses on a water-based surfactant free solution synthesis of SnSe, a highly relevant thermoelectric material. We show and rationalize that the number of leaching steps, purification solvent, annealing, and annealing atmosphere have significant influence on the Sn : Se ratio and impurity content in the powder. Such compositional changes that are undetectable by conventional characterization techniques lead to distinct consolidated materials with different types and concentration of defects. Additionally, the profound effect on their transport properties is demonstrated. We emphasize that understanding the chemistry and identifying key chemical species and their role throughout the process is paramount for optimizing material performance. Furthermore, we aim to demonstrate the necessity of comprehensive reporting of these steps as a standard practice to ensure material reproducibility.

High-pressure evolution of novel R2CuTiO6 (R = Tb – Lu) perovskite phases

Perovskite oxides of the R2CuTiO6 type with a trivalent rare earth element (R) at the A-cation site and co-occupancy of the B-cation site with the Jahn-Teller d9 Cu2+ and d0 Ti4+ transition metals, provides an interesting playground for various chemical and physical phenomena. However, conventional solid-state synthesis under ambient-pressure (AP) yields the perovskite structure only for the largest R constituents from La to Gd; with the smaller rare earth elements (Y, Tb–Lu) a non-perovskite (hexagonal BaTiO3-type) structure is formed. Here we demonstrate that through high-pressure (HP) high-temperature treatment, the hexagonal AP structure can be converted into a distorted (orthorhombic) perovskite structure for all the smaller R constituents. The critical pressure needed for the conversion increases with decreasing R3+ ion size, up to ca. 6 GPa for R = Lu. Moreover, a novel intermediate phase is found to form for most of the R constituents when pressures lower than the critical pressure are applied. We have employed both X-ray diffraction and UV–vis spectroscopy analyses to systematically follow the phase formation schemes for the different R constituents.

Influence of the La0.2Sr0.7Ti0.95Ni0.05O3 (LSTN) Synthesis Method on SOFC Anode Performance

Solid oxide fuel cells are characterized by a high efficiency for converting chemical energy into electricity and fuel flexibility. This research work focuses on developing durable and efficient anodes for solid oxide fuel cells (SOFCs) based on exsolving nickel from the perovskite structure. A-site-deficient La- and Ni-doped strontium titanates (La0.2Sr0.7Ti0.95Ni0.05O3−δ, LSTN) were synthesized using four different techniques and mixed with Ce0.8Gd0.2O2−δ (GDC) to form the SOFC anode. The synthesis routes of interest for comparison included solid-state, sol-gel, hydrothermal, and co-precipitation methods. LSTN powders were characterized via XRD, SEM, TPR, BET and XPS. In situ XRD during reduction was measured and the reduced powders were analyzed using TEM. The impact of synthesis route on SOFC performance was investigated. All samples were highly durable when kept at 0.5 V for 48 h at 800 °C with H2 fuel. Interestingly, the best performance was observed for the cell with the LSTN anode prepared via co-precipitation, while the conventional solid-state synthesis method only achieved the second-best results.

Investigation of crystal structural and magnetic properties of titanium doped Pr0.67Ba0.33MnO3 perovskite manganites

Pr0.67Ba0.33Mn1-xTixO3 (x = 0 and 0.02) were synthesized using a conventional solid-state synthesis method to investigate the effect of Ti substitution on their magnetic and electrical transport properties. All the samples were structurally evaluated by XRD diffraction Rietveld refinement method which showed an increase in unit cell volume with increasing Ni content, indicating that Ti is partially substituted at Mn. Scanning electron microscopy (SEM) and energy dispersive X-tray (EDX) are used to examine the surface morphology and identified elements in the samples' compounds. Fourier transform infrared spectroscopy (FTIR) reveals that all the samples exhibit a transmission band in the range of 590 cm-1 - 610 cm-1 . For x = 0, magnetization measurements showed paramagnetic (PM) to ferromagnetic (FM) transition at the transition temperature, TC ∼ 213 K. For Ti-substituted samples, ferromagnetic (FM) to PM transition was reduced with Curie temperature (TC), decreasing from 213 K (x = 0) to 205 K (x = 0.02). On the other hand, the M(H) showed the presence of a linear graph for x = 0 and x = 0.02 which may be related to the presence of paramagnetic at room temperature.

The interaction between Co and Mn ions on the magnetic frustration and the inducement of the double-exchange mechanism in hole-doped La0.6Dy0.1Ca0.3Co1-xMnxO3 (x = 0–1.0) cobaltite

This study investigates the interaction between Co and Mn ions on spin state behaviour and magnetic frustration in hole-doped La0.6Dy0.1Ca0.3Co1-xMnxO3 (x = 0–1.0) cobaltite. It aims to understand the inducement of the double-exchange (DE) mechanism in this system. The samples were synthesised using the conventional solid-state synthesis method, and their crystal structure and magnetic properties were analysed. Rietveld refinement of X-ray diffraction data confirmed that La0.6Dy0.1Ca0.3Co1-xO3 (x = 0.0 and 0.2) samples had rhombohedral crystals structure with R c − 3 space group. An orthorhombic (Pbnm) perovskite structure was observed for the La0.6Dy0.1Ca0.3Co1-xMnxO3 (x = 0.4 –1.0) accompanied by increasing cell volume in the samples as the substitution level of Mn increases. Temperature dependence of resistivity ρ(T) shows semiconducting behaviour in the whole temperature and composition range of x = 0.0–0.8. However, further substitution with x = 0.9 and x = 1.0 give remarkable induced MI behaviour where the MI transition temperature (TMI) increased from 75 K and 132 K, respectively. The result suggests that Mn ions play an important role in the magnetic properties of the cobaltite, and the system can be tuned by adjusting the Mn concentration.

Novel LiCa(PO3)3 and LiSr(PO3)3 microwave dielectric ceramics

Novel LiCa(PO3)3 and LiSr(PO3)3 phases were produced by conventional solid-state synthesis and formed into ceramic pellets followed by conventional sintering. The crystal structure, ceramic microstructure, microwave dielectric properties and ac conductivity were investigated. A triclinic space group P1- was obtained from Rietveld refinements, and the lattice vibration modes were determined by Raman spectroscopy. The optimum sintering conditions for LiCa(PO3)3 and LiSr(PO3)3 ceramics were 700 ℃ and 625 ℃, respectively, both for 10 h. Dense glass-free ceramic microstructures were confirmed by SEM. High relative densities of 94.6 % and 93.8 %, low microwave εr values of 5.85 and 5.62 at 14 GHz, and high quality factors Q×f of 25,200 and 23,450 GHz at 14 GHz were detected. Large negative τf of − 105 and − 106 ppm/°C were obtained, which are uncommon but highly valuable for offsetting positive τf values of other systems. Moderate Li+-ion conduction was detected in both compounds by ac impedance spectroscopy.

Crystal structure of the quaternary lithogallate Sr2LiGaO4

Abstract The new quaternary lithogallate Sr2LiGaO4 was prepared by conventional solid-state synthesis in a welded tantalum ampoule at T = 850 °C. Single-crystal X-ray diffraction was used to elucidate the crystal structure of the compound, which crystallizes in the orthorhombic space group Pnma (no. 62) with the lattice parameters a = 11.2434(4), b = 5.6879(2), and c = 6.6983(2) Å. The phase composition of the powder sample was determined by Rietveld refinement based on X-ray diffraction data. The crystal structure is composed of layers of corner-sharing LiO4 and GaO4 tetrahedra with alternating orientation parallel to the crystallographic bc plane. The eightfold coordinated strontium atoms are arranged in a zigzag manner between the layers forming two types of double-capped trigonal prismatic SrO8 units with common faces. The crystal structure of Sr2LiGaO4 is isotypic to that of the lithoaluminate derivate Sr1.85Ba0.15LiAlO4.

Room temperature ferromagnetism, optical band gap widening in Mg-doped ZnO compounds for spintronics applications

In the present research work, a conventional solid-state synthesis approach was used to synthesize the polycrystalline compound of Mg-doped ZnO (Zn1-xMgxO with x = 0–0.12). The XRD analysis reveals that Mg-doped compounds have been crystallized in a single hexagonal phase. The SEM analysis revealed that these compounds are constituted with microscopic spherical particles with a size range of 1–3 μm. Raman scattering spectra of these compounds displayed a blue-shift of the Raman active E2 (low) mode attributed to the vibration of zinc atom in wurtzite ZnO, indicating Mg ions were substituted successfully into the ZnO lattice. Optical measurements revealed that the optical band gap enhanced from 3.12 to 3.17 eV, while the transmittance value improved from 87% to 96% as the Mg doping percentage is increased. The magnetization (M) versus applied field (H) measurements, done at 300 K reveals that the undoped ZnO compound exhibits weak ferromagnetic behavior, whereas all Mg-doped ZnO compounds show a strong ferromagnetism with coercivity ranging between 85Oe≤Hc≤1482Oe, and with the highest saturation magnetization of 0.255 emu/gm for 12% Mg-doped sample.

Cost-effective microwave-assisted O3- type sodium-based layered oxide cathode materials for sodium-ion batteries

In this work, phase pure and highly crystalline O3-type layered oxide material (Na1Ni0.33Mn0.33Fe0.33O2-NNMF) was developed using; (i) a conventional solid-state synthesis route and (ii) a facile microwave-assisted sol–gel technique. A comparison of structural, thermal, and electrochemical properties is presented to elucidate the usefulness of the microwave-assisted sol–gel synthesis technique. A remarkable reduction in the sintering process time is noticed in the microwave-assisted sol–gel synthesis technique without compromising on the structural, thermal and electrochemical properties when compared to the conventional solid-state synthesis route confirming its decent cost-effectiveness. It is further noticed that NNMF developed through microwave-assisted sol–gel synthesis technique demonstrates superior thermal stability and comparable electrochemical performance as compared to the same material produced through the conventional sintering process. The decent electrochemical properties induced in NNMF during the microwave-assisted sol–gel synthesis technique can be attributed to the efficient diffusion of Na+ ions into/from the host structure during the intercalation/de-intercalation process as indicated by the high value of sodium diffusion coefficient (1 × 109-3.58 × 109m2s−1). The Potentiostatic Intermittent Titration Technique (PITT) analysis confirms single-phase Na+ intercalation/deintercalation in the host structure, regardless of the synthesis process. Finally, EIS analysis confirms the capacity fading of the developed materials during the cycling process is essentially due to an increase in the resistance with the increasing number of cycles due to the gradual thickening of formed SEI layer. The microwave-assisted sol–gel synthesis technique can be effectively employed for the production of many families of cathode materials at competitive cost facilitating their commercialization.

A comparative study of the effect of synthesis method on the formation of P2- and P3-Na0.67Mn0.9Mg0.1O2 cathodes

Na-ion batteries offer a way to develop large-scale energy storage necessary for the increased adoption of renewable energy sources. Layered transition metal oxide materials for electrodes can be synthesised using abundant and non-toxic materials, decreasing costs and risks compared to lithium-ion batteries. Solid state processing is commonly used for synthesis, using long calcinations at high temperatures (>800 °C). Other synthetic routes, such as biotemplating, offer the opportunity to reduce reaction temperatures and times, and can enable access to different polymorphs. Here, we compare the properties of Na0.67Mn0.9Mg0.1O2 synthesised by both solid state and biotemplating, producing both P2 and P3 polymorphs to understand the differences which arise as a result of synthesis and temperature choice. We show that biotemplated P3-Na0.67Mn0.9Mg0.1O2 offers increased discharge capacity over the more commonly reported P2 phase for 50 cycles at C/5, 103 mAh g−1 for biotemplated P3-NMMO. Furthermore, the biotemplating samples demonstrate improved capacity after 50 cycles at C/5, and higher capacity delivered at 5C in both P2 and P3 phases over conventional solid state synthesis.

On the photoluminescence of the solid solution LiBaLa1-xPrxWO6 (x = 0.0–1.0)

A set of compositions belonging to the solid solution LiBaLa1-xPrxWO6 (x = 0–1) were prepared by conventional solid state synthesis. Optical spectroscopy on single phase samples revealed that this solid solution delivers the most efficient member at a Pr3+ concentration of about 7%, which is rather high for a Pr3+ activated material. The decay time of the 3P0 → 3F2 transition is at 2,1 μs at 3 K, which can be considered as the radiative decay time due to the low temperature. From temperature dependent spectroscopy a thermal quenching temperature (T1/2) of 230 K could be derived. Due to the high density of about 7.22 g/cm3 also the luminescence upon 50 kV x-ray excitation was investigated. It turned out these materials show interesting luminescent behaviour upon x-ray excitation, with the resulting emission spectra being strongly dependent on the Pr3+ concentration.

Sub-10 nm Mixing and Alloying of Cu-Ag and Cu-Ni via Accelerated Solid Diffusion.

Development of nanoscale multicomponent solid inorganic materials is often hindered by slow solid diffusion kinetics and poor precursor mixing in conventional solid-state synthesis. These shortcomings can be alleviated by combining nanosized precursor mixtures and low temperature reaction, which could reduce crystal growth and accelerate the solid diffusion at the same time. However, high throughput production of nanoparticle mixtures with tunable composition via conventional synthesis is very challenging. In this work, we demonstrate that ∼10 nm homogeneous mixing of sub-10 nm nanoparticles can be achieved via spark nanomixing at room temperature and pressure. Kinetically driven Spark Plasma Discharge nanoparticle generation and ambient processing conditions limit particle coarsening and agglomeration, resulting in sub-10 nm primary particles of as-deposited films. The intimate mixing of these nanosized precursor particles enables intraparticle diffusion and formation of Cu/Ni nanoalloy during subsequent low temperature annealing at 100 °C. We also discovered that cross-particle diffusion is promoted during the low-temperature sulfurization of Cu/Ag which tends to phase-segregate, eventually leading to the growth of sulfide nanocrystals and improved homogeneity. High elemental homogeneity, small diffusion path lengths, and high diffusibility synergically contribute to faster diffusion kinetics of sub-10 nm nanoparticle mixtures. The combination of ∼10 nm homogeneous precursors via spark nanomixing, low-temperature annealing, and a wide range of potentially compatible materials makes our approach a good candidate as a general platform toward accelerated solid state synthesis of nanomaterials.

Optimizing the Mechanoluminescent Properties of CaZnOS:Tb via Microwave-Assisted Synthesis: A Comparative Study with Conventional Thermal Methods.

Recent developments in lighting and display technologies have led to an increased focus on materials and phosphors with high efficiency, chemical stability, and eco-friendliness. Mechanoluminescence (ML) is a promising technology for new lighting devices, specifically in pressure sensors and displays. CaZnOS has been identified as an efficient ML material, with potential applications as a stress sensor. This study focuses on optimizing the mechanoluminescent properties of CaZnOS:Tb through microwave-assisted synthesis. We successfully synthesized CaZnOS doped with Tb3+ using this method and compared it with samples obtained through conventional solid-state methods. We analyzed the material's characteristics using various techniques to investigate their structural, morphological, and optical properties. We then studied the material's mechanoluminescent properties through single impacts with varying energies. Our results show that materials synthesized through microwave methods exhibit similar optical and, primarily, mechanoluminescent properties, making them suitable for use in photonics applications. The comparison of the microwave and conventional solid-state synthesis methods highlights the potential of microwave-assisted methods to optimize the properties of mechanoluminescent materials for practical applications.

Rationalizing the alkali ions distribution along the honeycomb layered (Li,Na)2SnO3 pseudo solid solution

Alkali-rich layered oxides Li2SnO3 and Na2SnO3 are isostructural, but no alkali-mixed compositions have been reported so far. While the thermodynamic stability of such mixed compositions is predicted by DFT calculations mainly for the sodium-rich side, single-phase compounds Li2-xNaxSnO3 were successfully obtained in the whole composition range (0 ≤ x ≤ 2) by conventional solid-state synthesis thanks to a quenching procedure at the end of the heat treatment. From Li2SnO3 to Na2SnO2, the evolution of the cell parameters and the DFT calculations demonstrate that the lithium-to-sodium substitution occurs firstly inside the alkali layer up to Li0.5Na1.5SnO3 and then in the honeycomb layer.

Synthesis and Characterization of Oxide Chloride Sr2VO3Cl, a Layered S = 1 Compound.

The mixed-anion compound with composition Sr2VO3Cl has been synthesized for the first time, using the conventional high-temperature solid-state synthesis technique in a closed silica ampule under inert conditions. This compound belongs to the known Sr2 TmO3Cl (Tm = Sc, Mn, Fe, Co, Ni) family, but with Tm = V. All homologues within this family can be described with the tetragonal space group P4/nmm (No. 129); from a Rietveld refinement of powder X-ray diffraction data on the Tm = V homologue, the unit cell parameters were determined to a = 3.95974(8) and c = 14.0660(4) Å, and the atomic parameters in the crystal structure could be estimated. The synthesized powder is black, implying that the compound is a semiconductor. The magnetic investigations suggest that Sr2VO3Cl is a paramagnet at high temperatures, exhibiting a μeff = 2.0 μB V-1 and antiferromagnetic (AFM) interactions between the magnetic vanadium spins (θCW = -50 K), in line with the V-O-V advantageous super-exchange paths in the V-O layers. Specific heat capacity studies indicate two small anomalies around 5 and 35 K, which however are not associated with long-range magnetic ordering. 35Cl ss-NMR investigations suggest a slow spin freezing below 4.2 K resulting in a glassy-like spin ground state.

Microwave-assisted fast synthesis and red-emitting properties of a borotellurate-based phosphor with excellent thermostability

At present, with the increasing application needs of phosphor-converted white light-emitting diode (w-LED), the synthetic efficiency and thermal stability of phosphor become urgent problems. Herein, this research reports a microwave-assisted fast synthesis approach to obtain a Sm3+-activated borotellurate Na2Y2TeO4(BO3)2 (NYTB) red phosphor with high crystallinity, excellent thermostability, and low chromaticity shift. For the NYTB-based phosphor, in contrast to the conventional solid-state synthesis, the microwave-assisted synthesis method involves lower synthesis temperature and shorter processing time. Additionally, the concentration quenching mechanism was determined. The w-LED device packaged with the studied phosphor exhibits a near-standard white light with proper CCT and high Ra parameters.

Low-Temperature Ion Exchange Synthesis of Layered LiNiO2 Single Crystals with High Ordering

Layered Ni-rich oxide cathode materials are being explored in an effort to boost the energy density of lithium-ion batteries, especially for automotive applications. Among them, the ternary-phase LiNiO2 (LNO) is a promising candidate but brings along various issues, such as poor structural stability. The material is prone to disordering (Li off-stoichiometry) when prepared by conventional solid-state synthesis, leading to the presence of Ni2+ in the Li layer. These point defects negatively affect the utilization of the Li inventory, thereby limiting the practical specific capacity. In this work, we report on a two-step synthesis approach that avoids the formation of nickel substitutional defects. First, NaNiO2 (NNO) is prepared, showing no such defects due to larger differences in ionic radii between Ni2+/Ni3+ and Na+. NNO is then subjected to Na+/Li+ exchange under mild conditions. In so doing, monolithic LNO particles free of NiLi• defects can be produced at relatively low temperatures. Notably, this route allows for tailoring of the grain size, a strategy that may be used to gain insights into the structure–size–property relations in single-crystalline LNO.

Machine learning accelerated discovery of high transmittance in (K0.5Na0.5)NbO3-based ceramics

High optical transmittance (T%) has always been an important indicator of transparent-ferroelectric ceramics for optoelectronic coupling. However, the pathway of pursuing high transparency has been at the experimental trial-and-error stage over the past decades, manifesting major drawbacks of being time-consuming and resource-wasting. The present work introduces a machine learning (ML) accelerated development of highly transparent-ferroelectrics by taking potassium-sodium niobate (KNN)-based ceramics as the model material. It is highlighted that by using a small data set of 118 sample data and four key features, we predict the T% of un-synthesized KNN-based ceramics and evaluate the importance of key features. Meanwhile, the screened (K0.5Na0.5)0.956Tb0.004Ba0.04NbO3 ceramics were successfully realized by the conventional solid-state synthesis, and the experimental measured T% is in full agreement with the predicted results, exhibiting a satisfactory high T% of ~78% at 800 nm. In addition, ML is also used to explore the best experimental parameters, and the prediction results of T% are particularly sensitive to changes in sintering temperature (ST). Eventually, the predicted optimal ST is highly consistent with the experimental one. This study constructs a new avenue for exploring high T% ferroelectric KNN ceramics based on ML, ascertaining optimal process parameters, and guiding the development of other transparent-ferroelectrics in optoelectronic fields.

Centrosymmetric Tetragonal Tungsten Bronzes A4Bi2Nb10O30 (A = Na, K, Rb) with a Bi 6s Lone Pair

A first-principles study of the tetragonal tungsten bronze (TTB) K4Bi2Nb10O30 has suggested that the Bi 6s lone pair causes in-plane polarization (within the a–b plane), corresponding to the one found in Pb5Nb10O30 (PN), in contrast to the out-of-plane polarization (along c) found in most TTBs. Replacing PN with KBN potentially opens for a lead-free analogue to morphotropic phase boundaries known in TTBs based on PN. Here, we report on the synthesis and properties of A4Bi2Nb10O30 (ABN, A = Na, K, Rb) with the objective to determine the structure and electrical properties, paying particular attention to the role of the Bi 6s lone pair. The ABN materials were synthesized via conventional solid-state synthesis in a two-step process. Convergent-beam electron diffraction demonstrated a centrosymmetric tetragonal space group for the two compounds KBN and RBN, and ferroelectric polarization–electric field measurements confirmed the lack of hysteretic behavior in line with the observed centrosymmetric symmetry. Non-ambient powder X-ray diffraction demonstrated the signature of a phase transition for KBN and RBN, as several weak satellite reflections vanished during heating and reappeared upon cooling. Dielectric spectroscopy supported the observation of an anomaly due to the presence of a weak maximum in the electrical permittivity at temperatures corresponding to the disappearance of the satellite reflections. Possible explanations for the absence of polarization in ABN TTBs are discussed with particular attention to the suppression of the 6s2 lone pair effect of Bi and the size of A-site cations in the TTB crystal structure.