Solid-state Reaction Method Research Articles

Tổng hợp vật liệu LiNi0,9Mn0,05Co0,05O2 bằng phương pháp phản ứng pha rắn (NMC9.5.5-PR) ứng dụng chế tạo pin ion liti

Nickel-manganese-cobalt (NMC) transition metal oxide-based layered structural materials are evaluated a promising material for applications as cathode in lithium-ion batteries. In this study, we have successfully synthesized nickel-rich NMC material LiNi0.9Mn0.05Co0.05O2 by solid-state reaction method (NMC9.5.5- PR). The CR2032-type lithium-ion battery is also successfully fabricated from NMC material to serve the study of electrochemical properties. The NMC9.5.5-PR material exhibits outstanding discharge specific capacity when providing a maximum specific capacity of up to 212.4 mAh/g at a current density of 10 mA/g. However, the cycle efficiency survey results show that the NMC9.5.5-PR material has some disadvantages (only maintaining 81.6% of the discharge specific capacity after 50 continuous charge-discharge cycles at current density of 10 mA/g). These electrochemical properties indicate that it is necessary to further improve the cyclic efficiency of NMC9.5.5-PR material but preserving its outstanding electrical energy storage capacity. Successfully accomplishing this goal, we believe that NMC-9.5.5-PR or a material based on NMC9.5.5-PR will be one of the suitable materials to fabricate positive electrodes used in lithium-ion batteries.

Structural and Magnetic Properties of Barium-Strontium-Hexaferrite Material Ba0.6Sr0.4Fe10-xCoxMnTiO19 (x = 0.5; 1.0; and 1.5) as Microwave Absorbers

We discuss the structure properties of Ba0.6Sr0.4Fe10-xCoxMnTiO19(BSFCMTO) for x = 0.5, 1.0, and 1.5 that influence its magnetic properties as a microwave absorber. A solid-state reaction method using high-energy milling was used to synthesize hexaferrite. There were no structural changes when the Co2+ ion was substituted for the Fe3+ ion; the structures of all samples were hexagonal and the space group was P63/mmc. The surface morphology had heterogeneous particles with a size of 300 to 600 nm. The magnetic properties tended to decrease with an increasing number of Co2+ ion substitutions. The reflection loss (RL) had a minimum value of -14.89 dB. This value was reached at a frequency of 10.96 GHz and had a bandwidth at 1.24 GHz with a sample thickness of 1 mm in the Ba0.6Sr0.4Fe9.9Co0.1MnTiO19 sample.

Investigation of the magnetocaloric effect and critical behavior of the perovskite La0.65Ca0.35−xBaxMnO3 (x=0, 0.1, 0.2, 0.3)

Polycrystalline samples of La[Formula: see text]Ca[Formula: see text]BaxMnO3 (x = 0, 0.1, 0.2, 0.3) were prepared using a conventional solid-state reaction method. The prepared samples demonstrated good single-phase quality, characterized by a space group of Pbnm. There was a significant increase in the relative cooling power (at 5[Formula: see text]T), with values as follows: RCP[Formula: see text][Formula: see text]J[Formula: see text]⋅[Formula: see text]kg[Formula: see text], RCP[Formula: see text][Formula: see text]J[Formula: see text]⋅[Formula: see text]kg[Formula: see text], RCP[Formula: see text][Formula: see text]J[Formula: see text]⋅[Formula: see text]kg[Formula: see text], and RCP[Formula: see text][Formula: see text]J[Formula: see text]⋅[Formula: see text]kg[Formula: see text]. It is noteworthy that the sample with a doping level of x = 0.2 underwent a transition from a first-order phase transition to a second-order phase transition. The critical behavior of the x = 0.2 and 0.3 samples was analyzed using modified Arrott plots and the Kouvel–Fisher method to determine critical exponents. The results obtained from both methods were in close agreement, indicating that the critical behavior of the x = 0.2 and 0.3 samples can be described by the mean field model.

Effects of (KMn)3+ co-doping on the negative thermal expansion property of In2W3O12

At room temperature, monoclinic In2W3O12 ceramics exhibits positive thermal expansion. However, it transforms into an orthorhombic phase above 253 ℃, and then stably exhibits negative thermal expansion (NTE). In this work, to improve the NTE performance and extend the NTE temperature range of In2W3O12, the KxMnxIn2-xW3O12(0≤x≤0.5) ceramics were synthesized via the solid-state reaction method. The effects of (KMn)3+ double cation co-doping on the composition, microstructure, and thermal expansion behaviors of In2W3O12 ceramics were studied using XRD, Raman, XPS, SEM, and TMA. The results show that (KMn)3+ cations can replace In3+ in In2W3O12 ceramics. As the (KMn)3+ doping amount increases, monoclinic In2W3O12 gradually changed into monoclinic KxMnxIn2-xW3O12. Meanwhile, the grains grow up and the density of KxMnxIn2-xW3O12 ceramics was increased. Pure monoclinic KxMnxIn2-xW3O12 ceramics were prepared when x rises to 0.25 and 0.4. Among them, the thermal expansion coefficient of K0.4Mn0.4In1.6W3O12 ceramics in 100–700 ℃ is as high as -17.83×10-6 ℃-1, which was significantly improved compared to In2W3O12 ceramics. In addition, the structural phase transition of In2W3O12 ceramics around 253 ℃ was gradually eliminated and the NTE temperature range was widened. Double cation (KMn)3+ co-doping effectively improves the NTE performance of In2W3O12.

Utilizing rare earth titanates to improve performance of solid-state electrochromic device

Exploring new materials and synthesis recipes are required to enhance the electrochromic performance especially, when used in solid-state devices. Here, polycrystalline gadolinium titanate (Gd2TiO5 or GTO), synthesized using a simple solid-state reaction method, has been used for this purpose by combining it with polythiophene (P3HT). The electrochemical investigation of the Gd2TiO5 doped P3HT electrode has been carried out using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which reveals the dominance of diffusion-controlled mechanism over charge storage on the electrode surface as compared to the P3HT electrode. The Gd2TiO5 doped P3HT solid-state electrochromic device shows color modulation at 515 nm and 670 nm wavelengths with a color contrast of as high as 79% and 42%, respectively, under an external bias of as low as ±1.4 V. The prepared device switches between maroon to a transparent state in less than a second under the external bias (±1.4 V) with a high coloration efficiency of 346 cm2/C. The device shows improved cycle life over 100 switching cycles at both the wavelengths, which makes it more suitable for real-life applications.

Synthesis and erudite insight into the structural, luminescence and thermal sensing characteristics of Sm3+ incorporated [formula omitted]-BaB2O4 novel phosphors

In this paper, we have presented the comprehensive characterization of red-light-emitting novel β-BaB2O4:xSm3+ (x = 0.5, 0.75, 1, 1.5, and 2 mol%) phosphor samples synthesized by making use of solid-state reaction method. The XRD patterns verified the successful synthesis and in-depth analyses were carried out to explore the structural, luminescence, and thermal properties. Notably, the introduction of Sm3+ through doping did not result in any substantial alterations in the crystal structure. Photoluminescence (PL) emission spectra exhibited 4 distinct peaks for 401 nm excitation. Out of these 4 peaks, the prominent peak was present at 601 nm, attributed to the magnetic dipole-allowed transition 4G5/2 → 6H7/2. The colorimetric analysis revealed the correlated color temperature (CCT) to be around 1700 K, accompanied by 99.9 % colour purity. The optimal doping concentration, before luminescence quenching, was identified as 1 mol%, with multipole-multipole interactions identified as the predominant quenching mechanism. Diffuse reflectance spectroscopy (DRS) studies on β-BaB2O4:1%Sm3+ confirmed characteristic peaks corresponding to Sm3+ transitions, revealing an ionic bonding nature between Sm3+ and the host. Also, the direct optical band gap was determined to be 5.62 eV. Furthermore, the optimized phosphor demonstrated exceptional temperature-dependent photoluminescent (TDPL) properties, exhibiting a negligible (∼5 %) decrease in emission intensity for prominent peaks even at 440 K. Overall, the phosphors displayed high activation energy, significant thermal stability, and thermal sensing properties, making them promising candidates for various optoelectronic applications.

Impacts of diffusive ion migration on ferroelectric properties in BaTiO3 composite

Multiferroic composites, combining ferroelectric and ferromagnetic properties, hold significant promise in today’s technology landscape in a diverse array of fields including information storage devices, energy harvesters, current and magnetic field sensors, tunable devices, and various other domains. Exploring the interaction between these materials and their impact on multiferroic properties is crucial for advancing miniaturized, high-performance devices. A deeper understanding of the interplay between ionic dynamics and microstructure is essential for engineering these composites effectively. This study examines the deterioration of the ferroelectric property of BaTiO3 composite with the incorporation of the magnetic BaFe12O19. The composite is synthesized using the conventional solid-state reaction method. Structural analysis involves x-ray diffraction, Raman spectroscopy, and field-emission scanning electron microscopy. The dielectric and ferroelectric investigations, as well as magnetic analysis, are conducted. The study shows the existence of the electron hopping between different oxidation states of the cations and it elevates the material’s conductivity and, generates a leakage current that largely affects the ferroelectric properties by preventing saturation polarization.

Crystal structure, composition and valence state of cations in mixed-valence A1-xCdxMnO3 (A=Pr, La) ceramics

Abstract Complex manganites A1-xCdxMnO3 (A=Pr, La) are synthesized by solid state reaction method. Xray diffraction, scanning electron microscopy, and energy-dispersive analysis are applied to study their crystal structure, surface morphology, elemental and phase composition. X-ray photoelectron spectroscopy (XPS) methods are used to study the charge states of Pr and La cations, as well as to quantify the fractions of coexisting Mn3+ and Mn4+ ions. La3d-, La4d-, Pr4d- и Mn2p-spectra of ions La3+, Pr3+, Mn3+ and Mn4+ are calculated in the isolated–ion approximation with accounting for multiplet splitting and charge transfer effect. Good agreement with the experiment is obtained. The relative fractions of trivalent and tetravalent manganese ions in La0.45Cd0.78Mn0,9O2.86 and Pr0.49Cd0.74Mn0.85O2.91 are determined by fitting the Mn2p spectra by the superpositions of experimental spectra containing only Mn3+ and only Mn4+ ions; they were found to be 0.71Mn3+/0.29Mn4+ and 0.54Mn3+/0.46Mn4+, respectively.

Synergistic magnetoelectric enhancement in 0-3 particulate multiferroic composites: unveiling the exceptional interplay of Ba0.85Sm0.15TiO3 and Co0.85Sm0.15Fe2O4 phases for superior energy conversion.

This study investigates the complex investigation of the 0-3 particulate multiferroic properties found in composite materials. The materials used in this study are (1 - x)Ba0.85Sm0.15TiO3 (SmBT)-xCo0.85Sm0.15Fe2O4 (SmCF), and the research utilizes a combination of the solid-state reaction method and mechanical milling techniques. A cubic spinel secondary phase was discovered in Co0.85Sm0.15Fe2O4, while a tetragonal structure was found in Ba0.85Sm0.15TiO3. The M-H loops clearly indicate the presence of exchange interactions between spins with varying orientations within the domains. As the proportion of SmCF in the composites increased, the saturation magnetization and magnetic moments became stronger, indicating a greater level of exchange interactions. Through a temperature-dependent analysis, an increase was observed in both the dielectric constant (εr) and dielectric loss (tan δ). Nevertheless, there was a decrease in εr above the Curie temperature. It is worth mentioning that there was a significant increase in the magnetoelectric coupling constant, suggesting a stronger interaction between magnetic and electric fields. This increased interaction leads to a more effective conversion of electrical energy into its magnetic equivalent, indicating a significant improvement in overall energy efficiency. The results of our study shed light on a promising direction for the development of advanced multifunctional materials, which could have significant implications for energy-efficient applications.

Investigation of structural, dielectric and optical properties of the (Bi0.5La0.5Fe)0.5(Bi0.5Na0.5Ti)0.5O3perovskite for some electronic devices

This paper outlines the investigation of structural, dielectric, complex impedance and optical properties of lanthanum-modified (Bi[Formula: see text]La[Formula: see text]Fe)[Formula: see text](Bi[Formula: see text]Na[Formula: see text]Ti)[Formula: see text]O3 (BLF–BNT) single perovskite oxide synthesized by conventional solid-state reaction method. From Rietveld refinement, the crystal structure of the BLF–BNT ceramic has confirmed a tetragonal and the estimated average crystallite size is found to be 43.6[Formula: see text]nm. The dielectric properties of the La-doped BLF–BNT ceramic reveal the presence of Maxwell–Wagner-type dielectric dispersion. This suggests the occurrence of charge accumulation at grain boundaries and interfaces within the material. The complex impedance and complex electric modulus studies were employed to gain insight into the microscopic dielectric relaxations and conduction processes of the material. The electric modulus spectroscopy reveals the existence of nonDebye-type relaxation processes, including localized and long-range relaxation processes. The Nyquist and Cole–Cole plots show the semiconducting nature of the BLF–BNT ceramic. With the help of the Arrhenius method based on the imaginary portion of the electrical impedance and modulus, activation energies and relaxation times have been estimated. These parameters contribute to a deeper understanding of the electrical properties and conduction mechanisms within the material. Further, Raman spectroscopy, a nondestructive chemical analysis technique, was conducted to confirm the composition and structural integrity of the proposed system through its atomic vibrations. Also, the bandgap energy of the material has been estimated using Tauc’s relation and is found to be 1.69[Formula: see text]eV. This signifies that the BLF–BNT ceramic possesses a suitable bandgap for certain device applications, making it a promising candidate in various technological fields. Moreover, the overall comprehensive study of the proposed ceramic provides valuable insight and opens new possibilities for its potential applications in various electronic devices.

Structural, vibrational and optical characterisations of Li2Ba3(P2O7)2:Cr3+ by solid-state reaction method

ABSTRACT Cr3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowder was successfully synthesised by solid-state reaction technique. The nanopowder was characterised by several techniques. X-ray diffraction analysis reveals orthorhombic crystal structureand average crystallite size values 34.21 and 28.41 nm are determined by Debye Scherrer’s formula and Williamson-Hall (W-H) method. The morphology displayed both SEM and HR-TEM images are irregular stone-like shapes. EDS analysis confirms the constituted elements. The SAED patterns of HR-TEM with well matched with XRD data. FT-IR and Raman spectra analysis confirmed incorporation of Cr3+ in the Li2Ba3(P2O7)2 pyrophosphate nanopowder. The EPR spectrum exhibited signal at g = 1.968 which is attributed to interaction between Cr3+ and Cr3+ exchange pair. The site symmetry of Cr3+ ions occupy a distorted octahedral. Photoluminescence spectrum exhibited bands correspond to ultraviolet, blue and green regions. The evaluated CCT of 6517 K indicates yellowish-green emission near cold light which reveals that the present prepared sample is useful for LEDs applications.

Investigation of structural, thermo–electrical, and morphological features of the (Bi2O3)1–x–y (Tm2O3)x (Yb2O3)y ternary systems for intermediate temperatures

In this paper, the (Bi2O3)1–x–y (Tm2O3)x (Yb2O3)y ternary systems were successfully synthesized by the solid–state reaction method under air conditions. All powder compositions were then heat treated for 100 h at 750 °C to allow for partial substitution of dopant cations, Tm3+ and Yb3+, between host Bi3+ cations. Characterizations of fabricated compositions were carried out by XRD, TG and DTA, FPPT, and FE–SEM techniques. Stacked XRD patterns verified that all compositions included solely single–phase peaks, with the exception of Bi0.92Tm0.04Yb0.04O1.5–δ and Bi0.88Tm0.04Yb0.08O1.5–δ, whose patterns suggested mixed phases. The DTA curves, depending on temperature, detected the endothermic peaks at around 600 °C, implying that an order–disorder transition occurs in the anion sublattice of the doped crystal. At 700 °C, the conductivity of the Bi0.88Tm0.08Yb0.04O1.5–δ system was found to be 0.432 S/cm, surpassing the conductivity of a single–doped (Bi2O3)0.80 (Er2O3)0.20 system, which had a value of 0.37 S/cm at the same temperature.

Influence of excess sodium and phosphorus on the ionic conductivity of NASICON-structured Na3Zr2(SiO4)2PO4 ceramic solid electrolyte

NASICON-structured Na3Zr2(SiO4)2PO4 (NZSP) is regarded as one of the most promising solid-state electrolytes (SSEs) for all-solid-state Na-ion batteries mainly due to its high thermal stability and wide electrochemical window. However, the existing NZSP tends to exhibit lower ionic conductivity at room temperature. Thus, in order to solve this issue, NaH2PO4 was chosen as a novel phosphate source for the synthesis of NZSP via solid-state reaction method. On top of that, excess sodium (Na) and phosphorus (P) were also added into parent NZSP SSE with different weight percentage ratios to investigate their effects on Na+ ion activation energy. Structural study reveals NZSP with either excess Na or P have the same crystal structure morphology but are dissimilar in terms of the presence of impurities and grain size. NZSP with the excess of Na shows the highest ionic conductivity (1.05 × 10−3 S cm−1) and electrode polarization contributed by the increasing of Na+ carriers and the excess Na+ ion vacancies. These results authenticate that the excess of Na can be an effective way to improve the performance of NZSP SSE for energy storage application.

Dielectric Properties and Magnetoelectric Effect of Bi7Fe3Ti3O21 Ceramic Material Doped with Gadolinium Ions

Dielectric Properties and Magnetoelectric Effect of Bi7Fe3Ti3O21 Ceramic Material Doped with Gadolinium Ions

Polymer composites with magnetically active Eu-substituted NiZn ferrite fillers

In this research, the influence of Eu substitution on structural, quasi-static as well as dynamic (electro)magnetic properties of nickel zinc ferrites has been studied. The correlation of increasing europium content in the substituted NiZn ferrite filler with constant concentration (60 vol%) and the frequency dispersion of the complex permeability in magnetically active composite samples has been explored as well. Eu-substituted nickel-zinc ferrites with chemical composition Ni0.3Zn0.7EuxFe2-xO4, where x changes from 0.00 to 0.10 (step 0.02) ions per formula unit (i./f.u.), have been selected for their high initial permeability and in general good other magnetic parameters. On contrary, non-substituted ferrite of this composition exhibits undesirably low Curie temperature inconvenient for the use of these materials even at room temperatures. Therefore, Eu has been selected as a substituent for its known ability to increase the Curie temperature of prepared ferrites. The ferrites have been synthesized by means of the conventional solid state reaction method including double sintering at the temperatures of 950 °C and 1200 °C and used as magnetically active fillers incorporated into the magnetic polymer composites. Polyvinylchloride (PVC) has been used as the polymeric matrix. In spite of substituent amount x being the only parameter changing intentionally, the behavior of both the ferrite filler (deterministic until the creation of the second, non-magnetic, phase above x = 0.04) and the ferrite/PVC composites is quite hard to explain, and validate quantitatively, on the basis of simple theoretical assumptions. Nevertheless, the experiments confirmed positive effect of europium on the increase of Curie temperature. Also, the peak frequency of the imaginary component of the complex permeability has been found to be very sensitive to x, thus offering an effective tool for tuning the high-frequency properties of the composites useable for various applications, especially the shielding of microwave electromagnetic fields.

Enhanced Thermoelectric Performance of Na0.55CoO2 Ceramics Doped by Transition and Heavy Metal Oxides

Using the solid-state reactions method Na0.55(Co,M)O2 (M = Cr, Ni, Zn, W, and Bi) ceramics were prepared and their crystal structure, microstructure, electrophysical, thermophysical, and thermoelectric properties were studied. Doping of Na0.55CoO2 by transition or heavy metal oxides led to the increase in the grain size of ceramics, a decrease in electrical resistivity and thermal diffusivity values, and a sharp increase in the Seebeck coefficient, which resulted in essential enhancement of their thermoelectric properties. The largest power factor (1.04 mW/(m·K2) at 1073 K) and figure of merit (0.702 at 1073 K) among the studied samples possessed the Na0.55Co0.9Bi0.1O2 compound, which also demonstrated the highest values of the Seebeck coefficient (666 μV/K at 1073 K). The obtained results show that the doping of layered sodium cobaltite by different metal oxides allows for improving its stability, microstructure, and functional properties, which proves the effectiveness of the doping strategy for developing new thermoelectric oxides with enhanced thermoelectric performance.

Solid state synthesis, structural, DFT and spectroscopic analysis of EuAl3(BO3)4

Huntite-like borates are versatile and promising materials with wide range of applications in frequency conversion, UV light generation, lighting, displays, quantum information storage, and more, demonstrated by their various properties and uses in scientific research. In this work, EuAl3(BO3)4 powder was prepared through multi-stage solid-state reaction method using high-purity starting reagents: Eu2O3, Al2O3 and H3BO3, considering a 20 wt% excess of H3BO3 to compensate for B2O3 volatilization. Obtained samples undergo several treatments at varying temperatures and their phase purity is subsequently verified through powder X-ray diffraction analysis. The scanning electron microscopy reveals that resulting EuAl3(BO3)4 powder consists of granules exhibiting irregular morphologies with dimensions of 0.5–8 μm. The electronic band structure of EuAl3(BO3)4, calculated using the GGA PBE method, reveals f-states of Eu near 4 eV. These states do not produce emphasized peaks on simulated absorbance spectra. Using of DFT + U for the f-states of Eu pushed up f-bands above 6 eV and the charge transfer from p-O to d-Eu was obtained (Egdirect = 5.63 eV, Egindirect = 5.37 eV using Ueff = 4 eV). The variation of Ueff has a weak influence on the position of the bottom of the conduction band. The experimental bandgaps of EuAl3(BO3)4 crystalline powder, both direct and indirect, are found to be 3.96 and 3.67 eV, correspondingly. These values are lower than theoretical values what is associated with limitations of DFT calculations involving f electrons. The Raman spectrum of EuAl3(BO3)4 powder is discussed, detailing the contributions of different ions to specific spectral bands. Investigation of high-resolution luminescence spectra shows the possibility to estimate the content of defects by the testing the violation of the prohibition of ultranarrow 5D0 → 7F0 line that is forbidden in the ideal crystalline structure of trigonal EuAl3(BO3)4.

Structural refinement, dielectric and ferroelectric properties of Cr modified Ba0·90Sr0·10TiO3 ceramics

In this study, we investigated the impact of Chromium substitution on the structural, dielectric and ferroelectric characteristics of Ba0·90Sr0·10Ti1-3x/4CrxO3 (x = 0, 0.005, 0.010, 0.015 and 0.020) ceramics fabricated by solid state reaction method. Rietveld refinement of X-ray diffraction pattern confirmed tetragonal perovskite structure for all the samples. Based on the crystal structure and the lattice parameter obtained through XRD measurement, the Madelung energy of each sample was computed. SEM images revealed a reduction in grain size with rising Cr concentration. TEM, HRTEM, SAED and EDS analysis was carried out for BST-Cr3 sample. Diffused rings observed in Selective Area Electron Diffraction (SAED) patterns indicate the crystallinity of the sample. EDS analysis indicated the presence of Ba, Sr, Ti, O and Cr elements. In the temperature range of 30 °C–150 °C, dielectric measurements (dielectric constant ‘ε’ and tangent loss ‘tanδ’) have been made at different frequencies (1, 10, 50, 100 and 1000 kHz). The samples displayed a diffused phase transition, with noticeable reduction in Curie temperature ‘Tc’ and tangent loss ‘tanδ’ with the substitution of Cr. Polarization versus electric field loops were recorded at different electric fields (5, 10, 15, 20 and 25 kV/cm) and improved values of remnant polarization ‘Pr’ and coercive field ‘Ec’ were observed. A lower Ec value facilitates easier domain movement within the unit cell, leading to enhanced ferroelectric properties. Temperature dependent P-E loops indicated that as the temperature increased, the material became softer accompanied by simultaneous reduction in Pr and Ec values.

Enhanced photocatalytic removal of azo dye by the K3NaCo4(MoO4)6/H2O2 system

K3NaCo4(MoO4)6 photocatalyst has been prepared using a solid-state reaction method. First, its crystal structure is determined from single-crystal X-ray diffraction data. This material crystallizes in trigonal system, space group R3¯ (No.148) with cell parameters a = 14.434(3) Å and c = 19.811(6) Å. The crystal structure of the title compound can be described by the junction of ribbons and MoO4 tetrahedra by sharing vertices to give a three-dimensional framework in which Na+ and K+ cations are resided. Second, the as prepared sample has been characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, UV–visible spectroscopy, scanning electron microscope (SEM) and EDX analysis. The SEM analysis demonstrates the presence of agglomerates with uniform nanoparticles having different crystallite sizes. FTIR and Raman spectra confirm the presence of characteristic MoO4 tetrahedra. Moreover, the optical band gap was found to be 3.5 eV. Finally, the photocatalytic removal of Acid Yellow 23 (AY-23) organic azo dye was investigated under solar light in the presence of K3NaCo4(MoO4)6 photocatalyst and H2O2. A good photocatalytic activity for the degradation of AY-23 dye has been noted with a removal rate reaching 98 % when adding H2O2 at optimum reaction. The elimination of AY-23 increased with the addition of 5 mM H2O2 concentration. The rate constant of the photocatalytic process in the K3NaCo4(MoO4)6/H2O2 system is about 1.2 × 10-1h−1.

Cryogenic magnetocaloric effects of NaLnF4 (Ln = Gd, Tb, Dy, Ho, Er, Tm, and Yb)

Cryogenic refrigeration technology based on magnetocaloric effects plays a critical role in a variety of technological applications. In this paper, we report the cryogenic magnetocaloric effects of a series of sodium-rare earth fluoride samples (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb) synthesized by the solid-state reaction method. These compounds all crystallize in a hexagonal crystal structure. Down to 2 K, no magnetic ordering was detected, while all compounds show negative Curie–Weiss temperatures indicative of strong antiferromagnetic coupling. Magnetic fields effectively suppress the magnetic fluctuations, leading to a maximum magnetic entropy change of −56 J kg−1 K−1 in NaGdF4 at the magnetic field change from 0 to 50 kOe. These series of compounds are potentially excellent magnetic refrigerants at low temperatures.