Impurity Phases Research Articles

Green synthesis of aluminium-substituted calcium hexaferrite nanoparticles for high-frequency applications

As the first of their kind, Al3＋-substituted calcium hexaferrite (CaAlxFe12−xO19 (x=0, 1, 3, 5 and 7)) nanoparticles (NPs) were synthesized via a facile, economical, eco-friendly lemon juice extract-mediated green solution combustion method. The samples were calcined, followed by characterization. The Bragg reflections confirm the formation of a single-phase magnetoplumbite (M)-type hexaferrite crystal structure. No other impurity or mixed phases are observed even after the substitution of Al3＋ in the host matrix. The crystallite size decreases from 17 to 11 nm with an increase in the substitution of Al3＋ ions. Surface morphological analysis shows the presence of agglomerated irregularly shaped NPs. The direct band gap estimated with Wood and Tauc’s relation decreases from 4.22 to 3.76 eV with an increase in the substitution of Al3＋ ions. These Al3＋-substituted calcium hexaferrite NPs are predicted to be useful in high-frequency applications based on structural, dielectric, and magnetic studies.

Novel lanthanide-doped Y3-xNaxAl5-yVyO12 garnets: Synthesis, structural and optical properties

In this study the novel garnet-type Y2.47Na0.5Ln0.03Al5O12, Y2.97Ln0.03Al4.95V0.05O12, Y2.92Na0.05Ln0.03Al4.9833V0.0167O12 (Ln = Ce3+, Tb3+, Eu3+) phosphors were successfully synthesized by the sol-gel method for the first time. The structural, morphological and optical properties were characterized by using multiple characterization techniques. The XRD and FTIR results confirmed that all obtained phosphors are monophasic yttrium aluminium garnet compounds, i.e. the doping of Ce3+, Tb3+, Eu3+, Na+, V5+ ions does not induce any impurity phases, indicating the successful incorporation of these dopants into the YAG host. The formation of novel garnets was probed using 27Al, 51V, 23Na MAS NMR techniques. SEM micrographs revealed that almost in all cases, the surface of the obtained luminophores is porous and consists of homogeneously distributed irregular sphere-like shape particles, which tend to form larger agglomerates. The optical properties of obtained compounds were also investigated by recording their excitation and emission spectra and calculating the colour coordinates in the CIE 1931 colour space.

Mechanism Behind the Loss of Fast Charging Capability in Nickel-Rich Cathode Materials.

Fast charging technology for electric vehicles (EVs), offering rapid charging times similar to conventional vehicle refueling, holds promise but faces obstacles owing to kinetic issues within lithium-ion batteries (LIBs). Specifically, the significance of cathode materials in fast charging has grown because Ni-rich cathodes are employed to enhance the energy density of LIBs. Herein, the mechanism behind the loss of fast charging capability of Ni-rich cathodes during extended cycling is investigated through a comparative analysis of Ni-rich cathodes with different microstructures. The results revealed that microcracks and the resultant cathode deterioration significantly compromised the fast charging capability over extended cycling. When thick rocksalt impurity phases form throughout the particles owing to electrolyte infiltration via microcracks, the limited kinetics of Li+ ions create electrochemically unreactive areas under high-current conditions, resulting in the loss of fast charging capability. Hence, preventing microcrack formation by tailoring microstructures is essential to ensure stability in fast charging capability. Understanding the relationship between microcracks and the loss of fast charging capability is essential for developing Ni-rich cathodes that facilitate stable fast charging upon extended cycling, thereby promoting widespread EV adoption.

Large-Scale Green Synthesis of Magnesium Whitlockite from Environmentally Benign Precursor.

Magnesium whitlockite (Mg-WH) powders were synthesized with remarkable efficiency via the dissolution-precipitation method by employing an environmentally benign precursor, gypsum. Under optimized conditions, each 5.00 g of initial gypsum yielded an impressive amount of 3.00 g (89% yield) of Mg-WH in a single batch. Remarkably, no XRD peaks attributable to impurity phases were observed, indicating the single-phase nature of the sample. FT-IR analysis confirmed the presence of the PO43- and HPO42- groups in the obtained Mg-WH phase. The SEM-EDX results confirmed that Mg-WH crystals with homogeneous Ca, Mg, P, and O distributions were obtained. In previously published research papers, the synthesis of Mg-WH has been consistently described as a highly intricate process due to material formation within a narrow pH and temperature range. Our proposed synthesis method is particularly compelling as it eliminates the need for meticulous monitoring, presenting a notable improvement in the quest for a more convenient and efficient Mg-WH synthesis. The proposed procedure not only emphasizes the effectiveness of the process, but also highlights its potential to meet significant demands, providing a reliable solution for large-scale production needs in various promising applications.

Charting the Irreversible Degradation Modes of Low Bandgap Pb‐Sn Perovskite Compositions for De‐Risking Practical Industrial Development

AbstractThe commercialization of a solar technology necessitates the fulfillment of specific requirements both regarding efficiency and stability to enter and gain space in the photovoltaic market. These aims are heavily dependent on the selection of suitable materials, which is critical for suppressing any reliability risks arising from inherent instabilities. Focusing on the absorber material, herein the most suitable low bandgap lead‐tin composition candidate for all‐perovskite tandem applications is investigated by studying their degradation mechanisms with both widely available and advanced characterization techniques. Three irreversible degradation processes are identified in narrow bandgap Pb‐Sn perovskite absorbers: 1) Tin (Sn) oxidation upon air exposure, 2) methylammonium (MA) loss upon heat exposure, and 3) formamidinium (FA) and cesium (Cs) segregation leading to impurity phase formation. From an industrial perspective, it is proposed to refocus attention on FASn0.5Pb0.5I3 which minimizes all three effects while maintaining a suitable bandgap for a bottom cell and good performance. Moreover, a practical and highly sensitive characterization method is proposed to monitor the oxidation, which can be deployed both in laboratory and industrial environments and provide useful information for the technological development process, including, the effectiveness of encapsulation methods, and the acceptable time windows for air exposure.

Synthesis of nano-selenium and its effects on germination and early seedling growth of four crop plants

In this work, nano-selenium (NSe) with different shapes (wires, rods, and spherical particles) was synthesized by a wet chemical method. These synthesized products were characterized by x-ray powder diffraction (XRD) analysis, a field emission scanning electron microscope (FE-SEM) with an energy dispersive x-ray analyzer, and Raman spectroscopy. FE-SEM images revealed that nanowires with an average diameter of 30–50 nm and length of 3–5 µm, nanorods with lengths of 400–800 nm and diameters of about 20–50 nm, and spherical-shaped nanoparticles (NPs) with diameters ranging from 40 to 60 nm were successfully synthesized. The XRD and Raman analysis confirmed that all the produced NSe samples exhibited hexagonal single-phase crystalline structure with no impurity phase. All three NSe products (SeNWs, SeNRs, and SeNPs) with a concentration range of 25–150 mg/l were used to investigate the impact of shape and concentration on seed germination and seedling vigor of four different crop species, namely, green bean, okra, wheat, and radish. The results revealed that NSe at low concentrations (≤50 mg/l for SeNWs and ≤100 mg/l for SeNRs and SeNPs) can promote seed germination, plant growth, and development of all the studied crop species. However, NSe can adversely affect the growth of plants at higher concentrations (≥75 mg/l for SeNWs).

Enhanced photocatalytic degradation of pure and Cu-doped ZnO nanoparticles prepared under Co-precipitation method

The key goal of this study is to innovate the pure and 0.05, 0.10 and 0.15 wt.% of Cudoped ZnO NPs through co-precipitation technique. PXRD pattern shows the hexagonal crystal structure with no any phase impurity were observed for all the synthesized samples. From UV-Vis DRS spectra, band gap was obtained as 3.18, 3.24, 3.29 and 3.33 eV respectively for undoped, Cu-doped ZnO NPs (0.05, 0.10 and 0.15 wt.%). From SEM analysis, the agglomeration of rod-like morphology for pure ZnO NPs, spherical-like morphology for Cu-doped ZnO NPs (0.05 wt.%) and flake-like morphology for Cu-doped ZnO NPs (0.10 wt.%) and flower-like morphology for Cu-doped ZnO NPs (0.15 wt.%). The photocatalytic performance of the synthesized NPs was studied by the dye degradation of Methylene Blue (MB) under UV irradiation. The result exposed that, 0.15 wt.% of Cu-doped ZnO NPs is found to have efficient degradation candidate materials.

All‐Inorganic Perovskite Solar Cells: Modification Strategies and Challenges

Cesium‐based all‐inorganic wide‐bandgap perovskite solar cells (AIWPSCs) have been demonstrated with exceptional optoelectronic properties such as intrinsic optical wide‐bandgap and high thermal stability, which make them suitable candidates for the front sub‐cells of tandem solar cells (TSCs). Passivation of perovskite surface and interface is a matter of common interest in this community since all‐inorganic perovskites always suffer from non‐ideal crystallization such as phase impurity, high defect density, and non‐uniform morphology. Despite these shortcomings, numerous efforts have been devoted in recent years to pursuing high‐performance AIWPSCs, which exhibit an abruptly increased power conversion efficiency (PCE) from 2.9% to over 21.0%. In view of not having a thorough summary about the advancements on AIWPSCs, herein, a comprehensive review is given to highlight the recent device performance progress of AIWPSC, particularly focusing on the strategies to passivate the defects of all‐inorganic perovskite, namely, additive engineering, solvent engineering, interface modification, and the exploration of new charge transport materials (CTMs) for improving the phase stability and PCE of AIWPSCs. Finally, a conclusive outlook on AIWPSCs will be given to provide our perspectives aiming to inspire the further development of AIWPSCs.

Absence of 3a0 charge density wave order in the infinite-layer nickelate NdNiO2

A hallmark of many unconventional superconductors is the presence of many-body interactions that give rise to broken-symmetry states intertwined with superconductivity. Recent resonant soft X-ray scattering experiments report commensurate 3a0 charge density wave order in infinite-layer nickelates, which has important implications regarding the universal interplay between charge order and superconductivity in both cuprates and nickelates. Here we present X-ray scattering and spectroscopy measurements on a series of NdNiO2+x samples, which reveal that the signatures of charge density wave order are absent in fully reduced, single-phase NdNiO2. The 3a0 superlattice peak instead originates from a partially reduced impurity phase where excess apical oxygens form ordered rows with three-unit-cell periodicity. The absence of any observable charge density wave order in NdNiO2 highlights a crucial difference between the phase diagrams of cuprate and nickelate superconductors.

Molten salt assisted synthesis and structure characteristic for high conductivity fluorine doped Li1.3Al0.3Ti1.7P3O12 solid electrolytes

To address the safety concerns surrounding liquid electrolyte lithium-ion batteries, the development of a safe and reliable solid electrolyte with high ionic conductivity is of utmost importance. In recent years, the NASICON-type Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte has garnered increasing attention due to its impressive room temperature ionic conductivity and excellent chemical stability. However, its preparation is usually completed in high temperature up to 1000 ℃, which is high energy consumption. Herein, F-doped Li1.3Al0.3Ti1.7P3O12 solid electrolytes were synthesized by molten salt assisted synthesis with AlF3 as the precursor and flux, which were prepared at 800 ℃ with relative density of 95.39% and room temperature lithium ionic conductivity of 1.14 × 10−3 S cm−1. XRD results show that F doping can inhibit the formation of impurity phase LiTiPO5 to a certain extent, and is beneficial to improve the conductivity and density of LATP solid electrolyte. FT-IR spectra show that the addition of F changes the structural peak of PO43- and increases the number of bridge oxygen, thus enhancing the structural stability of LATP solid electrolyte. The SEM results show that the addition of F can promote the growth of grain at low temperature, increase the density of LATP electrolyte, and reduce the energy consumption. EDS, XPS and TEM results show that F has been successfully doped into LATP solid electrolyte crystals.

Understanding the Air‐Exposure Degradation Chemistry of the Sacrificial Cathode Additive Li5FeO4 for Li‐Ion Batteries

AbstractLi5FeO4 (LFO) is emerging as a promising prelithiation additive due to the high lithium donor capacity (>700 mAh g−1), cheap raw materials, good environmental adaptability, and reliable synthesis approach. However, LFO suffers from extremely poor air stability and the underlying mechanism remains elusive. Herein, LFO is subjected to different atmospheres (the main component of air) of O2, CO2, N2, and 30% humidity air to unravel its reaction mechanism with air and the interfacial chemistry. It is found that Li+ ions will escape from the LFO crystal lattice to construct Li2O, Li2CO3, and LiOH impurity phases with an obvious change of LFO surface morphology in contact with O2, CO2, and humidity air. These insulating species remarkedly inhibit Li+ ion diffusion from the material and thus lead to an increment of interfacial impedance and an apparent capacity degradation. Consequently, the initial charging capacity decays rapidly from 681.5 to 169.4 mAh g−1 (under O2) and to 54.8 mAh g−1 (under CO2), respectively. In this regard, a facile coating strategy is proposed on the surface of LFO to effectively improve its air stability.

Stepwise Tailoring of Perovskite Nucleation Dynamics and Defect Formation Using a Supersaturation‐Suppression Layer for Developing Efficient and Stable Perovskite Solar Cells

Tailoring crystal growth and defects in perovskites, a viable strategy for suppressing non‐radiative recombination, is widely employed for developing efficient and stable perovskite solar cells (PSCs). However, simultaneous tailoring of crystal growth and defects in PSCs is challenging owing to several limitations; for example, excessive interactions between additives and perovskite precursors impede crystallization, and additive‐induced impurity phases can substantially increase the defect density in perovskite films. In this study, we introduced a metal‐induced supersaturation‐suppression layer (SSL) as a pseudo‐additive interfacial layer to tailor the crystallization dynamics and defect formation in perovskite crystals in steps. The proposed perovskite modification process involves an SSL‐induced metal–halide ion reaction, which modulates the crystallization kinetics for grain growth and enables the formation of metal–halide complex anion adducts that can reduce crystalline defects and suppress non‐radiative recombination while facilitating preferential perovskite crystal growth by alleviating residual strains. Because of these stepwise synergistic effects, the SSL‐based PSCs exhibited significantly improved device performances (23.4%), low hysteresis losses, and enhanced atmospheric operational stability.

Effect of heat treatment on microstructure and properties of CrMnFeCoNiMo high entropy alloy coating

In this paper, CrMnFeCoNiMo high entropy alloy coating was prepared on 304 stainless steel by plasma cladding technology. The effects of different heat treatment processes on the microstructure, hardness, wear resistance and corrosion resistance of high entropy alloy coatings were studied. The XRD and SEM images of the coating show that the phase structure is mainly Ni–Cr–Co–Mo phase. The impurity phase-[CrFe] solid solution and Ni3Fe phase will be formed between 950 °C and 1050 °C. The homogenization effect of the coating composition is more excellent under the heat treatment conditions of 950 °C and more than 1 h holding time. The hardness of the coating is relatively high at 850 °C heat treatment temperature and holding for 1 h, which is 670 HV0.2. When the temperature rises to 950 °C and 1050 °C, the hardness of the coating decreases. The coating has relatively high wear resistance at 950 °C heat treatment temperature and holding for 1 h, and the friction coefficient is about 0.27. Moreover, under this heat treatment condition, the surface composition of the coating is uniform and the corrosion resistance is good. The self-corrosion current is 1.325 × 10−7 A and the self-corrosion potential is −0.202 V.

Dual-Hyperspectral Optical Pump-Probe Microscopy with Single-Nanosecond Time Resolution.

In recent years, optical pump-probe microscopy (PPM) has become a vital technique for spatiotemporally imaging electronic excitations and charge-carrier transport in metals and semiconductors. However, existing methods are limited by mechanical delay lines with a probe time window up to several nanoseconds (ns) or monochromatic pump and probe sources with restricted spectral coverage and temporal resolution, hindering their amenability in studying relatively slow processes. To bridge these gaps, we introduce a dual-hyperspectral PPM setup with a time window spanning from nanoseconds to milliseconds and single-nanosecond resolution. Our method features a wide-field probe tunable from 370 to 1000 nm and a pump spanning from 330 nm to 16 μm. We apply this PPM technique to study various two-dimensional metal-halide perovskites (2D-MHPs) as representative semiconductors by imaging their transient responses near the exciton resonances under both above-band gap electronic pump excitation and below-band gap vibrational pump excitation. The resulting spatially and temporally resolved images reveal insights into heat dissipation, film uniformity, distribution of impurity phases, and film-substrate interfaces. In addition, the single-nanosecond temporal resolution enables the imaging of in-plane strain wave propagation in 2D-MHP single crystals. Our method, which offers extensive spectral tunability and significantly improved time resolution, opens new possibilities for the imaging of charge carriers, heat, and transient phase transformation processes, particularly in materials with spatially varying composition, strain, crystalline structure, and interfaces.

(Zn2+ + Cd2+) co-doped CaCu3Ti4O12 ceramics with enhanced dielectric permittivity and reduced dielectric loss tangent

The present study systematically investigated the structure, dielectric properties, and electrical response of Ca1-xCdxCu3-yZnyTi4O12 (x = y = 0, 0.025, 0.05, and 0.10). The XRD analysis indicates the presence of a CaCu3Ti4O12 phase in all the sintered ceramics, with no indications of impurity phases found. Achieving high dielectric permittivity and low loss tangent can be accomplished through codoping with Zn2+/Cd2+. At room temperature and 1 kHz, the Ca0.95Cd0.05Cu2.95Zn0.05Ti4O12 ceramic has a high dielectric constant of ∼1.61 × 105 and a low loss tangent of ∼0.03. In addition, codoping ions can enhance the stability of dielectric permittivity with respect to temperature variations. The utilization of impedance spectroscopy as a technique confirms the heterogeneous microstructure observed in sintered materials. The results of this investigation suggest a potential association between the internal barrier layer capacitor model and the underlying cause of the colossal dielectric characteristics observed in Ca1-xCdxCu3-yZnyTi4O12 materials. The analysis of X-ray photoelectron spectroscopy indicates the presence of Cu+ and Ti3+ species, which could potentially exert a significant impact on the development of n-type semiconducting grains in Ca1-xCdxCu3-yZnyTi4O12 ceramics. This influence is attributed to the existence of oxygen vacancies. Theoretical simulations revealed that a Zn atom is situated in proximity to a Cd atom within the CCTO structure. Furthermore, our findings indicate that the oxygen vacancy does not interact with the dopants. Our electron density analysis suggests that the presence of Cu+ and Ti3+ ions, as observed by XPS measurements, is a consequence of the existing oxygen vacancy.

Revealing effect of cobalt dopant on crystallography and optical characteristics of nanostructured cupric oxide

Cupric oxide is an interesting semiconducting material that has the potential to be applied in various technological utilizations. To understand the modified structure, the effects of Co doping at different concentrations (0, 1, 3, and 5 mol%) on the crystal structure, morphology, and optical properties of CuO nanoparticles synthesized by the co-precipitation method through heating at 400 °C for 2 h have been investigated. Synthesized samples were characterized by various techniques. X-ray diffractometer (XRD) results showed a monoclinic structure of CuO and impurity phase Co2O3 appearing when doping 5 mol% Cobalt. The crystallite size was found in the range of 25–48 nm. The crystallinity, texture coefficient, crystallite size, lattice constants, strain, and some physical properties (stress, Young's modulus, and strain energy) were calculated from the obtained XRD data. As a result, the lower Young's modulus and strain energy values of (111) crystal plane promoted the preferable growth in the direction. Fourier transform infrared spectrometer (FT-IR) was used to understand the chemical structure and confirm the substitution of Co in the samples. Scanning electron microscopy technique (SEM) was used to study morphology, appearing in the micron irregular flat plates that change to spherical particles when cobalt addition increases. Transmission electron microscope (TEM) micrographs show that structures of CuO are highly crystalline in nature and also provide clear evidence of spherical nanostructures in the Co-doped CuO. The Brunau–Emmet–Teller analysis method (BET) depicts a surface area improvement, showing 6.532 m2/g for the CuO and 19.285 m2/g for the 5 mol% Co-doped CuO sample. As more Co content, the decreasing energy bandgap of 2.75 to 2.58 eV was approximated using the Ultraviolet–Visible spectroscopy (UV–Vis) result. Photoluminescence spectra (PL) were found at about 440 and 470 nm, replied to oxygen vacancy (Vo) and copper vacancy (VCu), which are a sublevel affecting energy bandgap change. The role of Co dopant in improving the morphology and optical properties was discussed, associating with the structural characteristics and emerging intrinsic defects.

Tartrate-gel synthesized BaFe12-xCuxO19 (0 ≤ x ≤ 1) nanoceramics: Magnetic and catalytic properties

Magnetic catalysts present distinct advantages over their non-magnetic counterparts, primarily due to their ease of recovery from the reaction mixture through magnetic separation. Herein, magnetic and catalytic properties of Cu-substituted barium hexaferrite (BaFe12-xCuxO19, 0 ≤ x ≤ 1) nanoceramics, synthesized via a tartrate-gel method, are evaluated. Using XRD, FTIR, Raman, SEM, XPS, and VSM techniques, the synthesized compositions were characterized. The powder XRD analysis revealed that all samples predominantly consisted of hexaferrite phase, with small impurity phases, α-Fe2O3, CuO and BaFe2O4. The structural parameters (a, b, c), extracted from Rietveld refinement analysis, increased with ‘x’, primarily due to substitution of smaller Fe3+ cation by larger Cu2+ cation. The FTIR and Raman spectra of the samples exhibited characteristic bands corresponding to the M-type hexaferrite. A red-shift occurred in these bands as the Cu amount increased in the Ba-hexaferrite lattice, owing to increase in metal-oxygen bond length. Due to sintering aid nature of copper, considerable increase in the particle size is observed with inclusion of Cu. XPS spectral analysis indicated the oxygen defects in the Cu-substituted sample. The magnetic parameters (MS, HC, and K1) are found to decrease upon incorporation of Cu ions into the Ba-hexaferrite crystal structure. Conversely, the Curie temperature (TC) showed a slight increase with Cu content ‘x’. The unsubstituted sample (x = 0) exhibited no catalytic activity in the reduction of nitrophenol, whereas both Cu-substituted samples displayed enhanced activity with comparable rate constants (0.02 min−1). This activity was attributed to the presence of Cu ions at the octahedral sites (2a or 4f2). Additionally, a magnetic separation process followed by a reusability test was conducted for the x = 0.5 sample over five successive cycles. The consistent activity observed in each cycle underscored the robustness of the engineered magnetic catalyst.

Molten Salt Synthesized CaTa4O11:Er3+/Yb3+ with Superior Upconversion Luminescence.

Low phonon tantalate-based phosphors with a layer structure are considered to have excellent upconversion luminescence (UCL) intensity, which could be reduced due to the existence of impure phase defects and inappropriate doped rare earth ions. To improve their UCL performance, we have prepared single-phase CaTa4O11:Er3+/Yb3+ samples by a molten salt synthesis (MSS) using KCl as the reaction medium and compared its UCL properties with counterparts made by a conventional solid-state reaction (SSR) in this study. We have demonstrated that the MSS samples have a much higher UCL intensity under 980 nm laser excitation than the SSR ones due to accurate replacement of Ca2+ sites by Er3+/Yb3+ in high-purity single-phase MSS samples. We have further enhanced the green UCL intensity of the MSS samples by 1.57 times via acid picking (AP). Under 980 nm laser excitation at a high powder density of 61.3 W/cm2, the green UCL intensity of the MSS-AP samples can reach 3.72 times that of the SSR-AP samples. For potential luminescence thermometry applications, the maximum absolute sensitivity (SA) of the MSS-AP samples reaches 0.01316 K-1 at 501 K based on the luminescence intensity ratio. This study shows that CaTa4O11:Er3+/Yb3+ phosphors prepared by the MSS method are single-phase samples with excellent pure green UCL as a suitable temperature sensing material.

Structural and electrical characteristics of manganese modified BaTiO3 ceramic

The material Ba(Ti0.5Mn0.5)O3 synthesized through the conventional solid-state reaction method has hexagonal structure free from any impurity phase. The complex dielectric dispersion, temperature and frequency-dependent dielectric, impedance, AC conductivity, and leakage behavior of the sample are studied. The impedance study of the material encloses non-Debye type relaxation, negative temperature coefficient of resistance nature and the grain and grain boundary effects. The ferroelectric to paraelectric phase transition occurs at T C ∼ 270 °C. The dielectric constant and loss-tangent values are found to be less as compared to that of the parent barium titanate sample. R g < R gb, that is, grain boundary has greater opposition than the grain region. The material follows correlated barrier hopping model. The carrier transport process through AC conductivity study obeys the Jonscher’s power law and the Arrhenius relation while varying with the frequency and temperature.

Thermoelectric properties of Co doped TiNiCo&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sn alloys fabricated by melt spinning

Although TiNiSn-based half-Heusler thermoelectric materials obtain high power factors, their high lattice thermal conductivity greatly hinders the improvement of thermoelectric properties. In this work, TiNiCo&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sn (&lt;i&gt;x&lt;/i&gt; = 0–0.05) samples are prepared by melt spinning combined with spark plasma sintering method, and their phase, microstructure and thermoelectric properties are studied. The XRD results show that the main phase of all samples is TiNiSn phase, and no any other impurity phases are found, indicating that the high purity single phase can be prepared by rapid quenching process combined with SPS process. In the solidification process, the large cooling rate (10&lt;sup&gt;5&lt;/sup&gt;–10&lt;sup&gt;6&lt;/sup&gt; K/s) is conducive to obtaining the uniform nanocrystalline structure. The grains are closely packed, with grain sizes in a range of 200–600 nm. The grain sizes decrease to 50–400 nm for the Co-doping samples, which indicates that Co doping can reduce the grain size. For the &lt;i&gt;x&lt;/i&gt; = 0 sample, the thermal conductivity of the rapid quenching sample is significantly lower than that of bulk sample, with an average decrease of about 17.8%. Compared with the TiNiSn matrix, the Co-doping sample has the thermal conductivity that decreases significantly, and the maximum decrease can reach about 38.9%. The minimum value of lattice thermal conductivity of TiNiCo&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sn samples is 3.19 W/(m·K). Therefore, Co doping can significantly reduce the &lt;i&gt;κ&lt;/i&gt;&lt;sub&gt;l&lt;/sub&gt; values of TiNiCo&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sn (&lt;i&gt;x&lt;/i&gt; = 0.01–0.05) samples. With the increase of Co doping amount &lt;i&gt;x&lt;/i&gt;, n/p transition is observed in the TiNiCo&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sn samples, resulting in gradually reducing the conductivity and the power factor, and finally deteriorating the electrical transport performance, of which, the TiNiSn sample obtains the highest power factor of 29.56 W/(m·K&lt;sup&gt;2&lt;/sup&gt;) at 700 K. The &lt;i&gt;ZT&lt;/i&gt; value decreases with the Co doping amount &lt;i&gt;x&lt;/i&gt; increasing, and the maximum &lt;i&gt;ZT&lt;/i&gt; value of TiNiSn sample at 900 K is 0.48. This work shows that the thermal conductivity of TiNiSn can be effectively reduced by using the melt spinning process and magnetic Co doping.