A multi-color persistent luminescent phosphor β-NaYF4:RE3+ (RE = Sm,Tb, Dy,Pr) for dynamic anti-counterfeiting

Conventional luminescent materials generally exhibit uni-color and transient emission under UV excitation, which makes them mediocre in the field of anti-counterfeiting. The high-level anti-counterfeiting techniques are always becoming more complicated and in need of multi-color and persistent luminescent materials. Herein, we report a series of β-NaYF₄:RE³⁺ (RE = Sm, Tb, Dy, Pr) persistent luminescent phosphors with multi-color emitting and ultra-long persistent luminescence under the irradiation of X-rays. The effects of doping concentrations of RE³⁺ on the size, morphology, radioluminescence and afterglow performance of the products are investigated in detail. Hexagonal structured rod-like β-NaYF₄:Tb³⁺ crystals show super strong X-ray response and the afterglow signal lasts for up to seven days after X-rays are turned off. Upon X-rays irradiation, some of the F⁻ ions are expected to escape from the crystal lattice by elastic collisions, leading to the generation of Frenkel defects: the F vacancies and interstitials , which capture electrons and release them slowly to achieve different afterglow emission times. Taking advantages of the extraordinary radioluminescence performance of the β-NaYF₄:RE³⁺ persistent luminescent phosphors, the dynamic anti-counterfeiting patterns that containing rich time-resolved information were successfully designed.

A dynamic anti-counterfeiting pattern was successfully designed by using the excellent luminescence characteristics of long afterglow materials under X-ray excitation.     

(Ba,Sr)TiO3:RE perovskite phosphors (RE = Dy,Eu): nitrate pyrolysis synthesis,enhanced photoluminescence,and reversible emission against heating

A series of (Ba,Sr)TiO₃ phosphors singly doped with Eu³⁺ and Dy³⁺ were successfully synthesized using the nitrate pyrolysis method at 750 °C. Eu³⁺ or Dy³⁺ single-doped BaTiO₃ retained the tetragonal crystal structure of the host, while the Sr²⁺-substituted (Ba,Sr)TiO₃:RE³⁺ (RE³⁺ = Eu³⁺ or Dy³⁺) experienced a phase transformation from tetragonal to cubic phase with a unit cell shrinkage. For Eu³⁺ doped phosphors, BaTiO₃:xEu³⁺ (x = 0.02–0.10) exhibited red photoluminescence and the highest intensity of emission belonged to the optimal-doped BaTiO₃:xEu³⁺ (x = 8 mol%). Moreover, the substitution of 30 mol% Sr²⁺ for Ba²⁺ (that is Ba_0.7Sr_0.3TiO₃:xEu³⁺, x = 8 mol%) further enhanced the emission intensity of BaTiO₃:xEu³⁺ (x = 8 mol%). For Dy³⁺ doped phosphors, BaTiO₃:xDy³⁺ (x = 0.02–0.10) showed yellow photoluminescence and the highest light intensity was from the optimal-doped BaTiO₃:xDy³⁺ (x = 4 mol%). In addition, the substitution of 20 mol% Sr²⁺ for Ba²⁺ (the phosphor Ba_0.8Sr_0.2TiO₃:xDy³⁺, x = 4 mol%) induced further increase in emission intensity of BaTiO₃:xDy³⁺ (x = 4 mol%). The emission intensities at higher temperature of 100 °C retained about 70% and 90% of the initial values at room temperature (RT) for the optimal BaTiO₃:xEu³⁺ (x = 8 mol%) and BaTiO₃:xDy³⁺ (x = 4 mol%) phosphors, respectively, while the emission intensities at the temperature of 100 °C retained about 60% and 80% of the initial intensities at RT for the optimal Sr²⁺-substituted Ba_0.7Sr_0.3TiO₃:xEu³⁺ (x = 8 mol%) and Ba_0.8Sr_0.2TiO₃:xDy³⁺ (x = 4 mol%) phosphors, respectively. It is worth noting that on cooling down to RT again from 210 °C, the BaTiO₃:xDy³⁺ (x = 4 mol%) phosphor exhibited excellent luminescent thermal stability (with a high activation energy of 0.387 eV) and the strongest recovery (∼95%) of PL emission among the series of phosphors. The as-prepared phosphors with optimal compositions would be good candidates for the applications in lighting, display, and related fields.

Eu³⁺ and Dy³⁺ doped (Ba,Sr)TiO₃ red and yellow phosphors were synthesized respectively. Substituting of Sr²⁺ for Ba²⁺ further enhance emission. BaTiO₃:0.04Dy³⁺ possess an excellent thermal stability and the strongest emission recovery of 95% among the phosphors.     

Improved hydrogen storage kinetics of nanocrystalline and amorphous Ce–Mg–Ni-based CeMg12-type alloys synthesized by mechanical milling

In this paper, ball milling was used to prepare CeMg₁₁Ni + x wt% Ni (x = 100, 200) alloys having nanocrystalline and amorphous structures. The structures of the alloys and their electrochemical and gaseous kinetic performances were systematically investigated. It was shown that the increase in Ni content was beneficial to the formation of nanocrystalline and amorphous structures, and it significantly enhanced the electrochemical and gaseous hydrogen storage performances of as-milled alloys. In addition, the hydrogen storage capacities of the alloys fluctuated greatly with variation in milling duration. The maximum values of hydrogen capacity detected by varying the milling durations were 5.949 wt% and 6.157 wt% for x = 100 and 200 alloys, respectively. Similar results were observed for the hydriding rates and high-rate discharge abilities (HRD) of the as-milled alloys. The dehydriding rate increased with the increase in milling duration. The reduction in hydrogen desorption activation was the reason for enhanced gaseous hydrogen storage kinetics.

Addition of Ni and milling are beneficial for forming nanocrystalline and amorphous structures, thus enhancing the hydrogen storage kinetics of CeMg₁₂-type alloys.     

Half-metallicity in new Heusler alloys Mn2ScZ (Z = Si,Ge, Sn)

Study of half-metallicity has been performed in a new series of Mn₂ScZ (Z = Si, Ge and Sn) full Heusler alloys using density functional theory with the calculation and implementation of a Hubbard correction term (U). Volume optimization in magnetic and non-magnetic phases for both the Cu₂MnAl and Hg₂CuTi type structures was done to predict the stable ground state configuration. The stability was determined by calculating their formation energy as well as from elastic constants under ambient conditions. A half-metal is predicted for Mn₂ScSi and Mn₂ScGe with a narrow band gap in the minority spin whereas Mn₂ScSn shows a metallic nature. The magnetic moments of Mn and Sc are coupled in opposite directions with different strengths indicating that the ferrimagnetic order and the total magnetic moment per formula unit for half-metals follows the Slater Pauling rule. And a strong effect was shown by the size of the Z element in the electronic and magnetic properties.

Study of half-metallicity has been performed in a new series of Mn₂ScZ (Z = Si, Ge and Sn) full Heusler alloys using density functional theory with the calculation and implementation of a Hubbard correction term (U).     

Hydrogen storage in Mg2Ni(Fe)H4 nano particles synthesized from coarse-grained Mg and nano sized Ni(Fe) precursor

In this work, Mg₂Ni(Fe)H₄ was synthesized using precursors of nano Ni(Fe) composite powder prepared through arc plasma method and coarse-grained Mg powder. The microstructure, composition, phase components and the hydrogen storage properties of the Mg–Ni(Fe) composite were carefully investigated. It is observed that the Mg₂Ni(Fe)H₄ particles formed from the Mg–Ni(Fe) composite have a diameter of 100–240 nm and a portion of Fe in the Ni(Fe) nano particles transformed into α-Fe nano particles with the diameter of 40–120 nm. DSC measurements showed that the peak desorption temperature of the Mg₂Ni(Fe)H₄ was reduced to 501 K and the apparent activation energy for hydrogen desorption of the Mg₂Ni(Fe)H₄ was 97.2 kJ mol⁻¹ H₂. The formation enthalpy of Mg₂Ni(Fe)H₄ was measured to be −53.1 kJ mol⁻¹ H₂. The improvements in hydrogen sorption kinetics and thermodynamics can be attributed to the catalytic effect from α-Fe nano particles and the destabilization of Mg₂NiH₄ caused by the partial substitution of Ni by Fe, respectively.

Mg₂Ni(Fe)H₄ was synthesized from precursors of coarse grained Mg powder and Ni(Fe) nano particles with improved hydrogen sorption kinetics and thermodynamics as compared to Mg₂Ni(Fe)H₄.     

Evaluation of the microstructure,optical properties and hopping conduction mechanism of rare earth doped Ba0.85Ca0.12RE0.03Ti0.90Zr0.04Nb0.042O3 ceramics (RE = Ce3+ and Pr3+)

The current research work examines the impact of Rare Earth (RE³⁺) ion substitution on the structural, optical and conduction properties of a Ba_0.85Ca_0.12RE_0.03Ti_0.90Zr_0.04Nb_0.042O₃ (BCRETZN) (RE = Ce, Pr) ceramic compound produced via a solid-state route. The Rietveld method of the X-ray data revealed a tetragonal (P4mm) structure at room temperature for our ceramic compound. The morphology of the compound was explored using Scanning Electron Microscopy (SEM) as well as optical response and conduction behavior. The photoluminescence properties revealed that the BCPrTZN sample results in green and red photoemissions under laser excitation at 450 nm at RT. Furthermore, for the BCCeTZN sample, the photoluminescence data demonstrated that strong violet emission bands were acquired, at RT upon an excitation at 350 nm. The electrical conduction process was verified via the correlated barrier Hopping method. The scaling behavior suggests that the electrical conduction mechanism is independent of temperature. The existence of Ce³⁺ and Pr³⁺ ions in these materials could have important technological potential in new multifunctional devices.

This work examines the impact of rare earth (RE³⁺) ion substitution on the structural, optical and conduction properties of a Ba_0.85Ca_0.12RE_0.03Ti_0.90Zr_0.04Nb_0.042O₃ (BCRETZN) (RE = Ce, Pr) ceramic compound produced via a solid-state route.     

Enhanced hydrogen storage kinetics and air stability of nanoconfined NaAlH4 in graphene oxide framework

With a growing concern over climate change, hydrogen offers a wide range of opportunities for decarbonization and provides a flexibility in overall energy systems. While hydrogen energy is already plugged into industrial sectors, a physical hydrogen storage system poses a formidable challenge, giving momentum for safe and efficient solid-state hydrogen storage. Accommodating such demands, sodium alanate (NaAlH₄) has been considered one of the candidate materials due to its high storage capacity. However, it requires a high temperature for hydrogen desorption and becomes inactive irreversibly upon air-exposure. To enhance sluggish reaction kinetics and reduce the hydrogen desorption temperature, NaAlH₄ can be confined into a porous nanoscaffold; however, nanoconfined NaAlH₄ with sufficient hydrogen storage performance and competent stability has not been demonstrated so far. In this work, we demonstrate a simultaneously enhanced hydrogen storage performance and air-stability for NaAlH₄ particles confined in a nanoporous graphene oxide framework (GOF). The structure of the GOF was elaborately optimized as a nanoscaffold, and NaAlH₄ was infiltrated into the pores of the GOF via incipient wetness impregnation. As a result of the nanoconfinement, both the onset temperature and activation energy for hydrogen desorption of NaAlH₄ are significantly decreased without transition metal catalysts, while simultaneously achieving the stability under ambient conditions.

NaAlH₄ nanoconfined in a graphene oxide framework (NaAlH₄@GOF) showed significantly enhanced hydrogen storage kinetics as well as improved oxidative stability under ambient conditions.     

Impact of rare earth (RE3+ = La3+, Sm3+) substitution in the A site perovskite on the structural,and electrical properties of Ba(Zr0.9Ti0.1)O3 ceramics

Undoped Ba(Zr_0.9Ti_0.1)O₃ and rare-earth-doped (Ba_1−xRE_2x/3)(Zr_0.9Ti_0.1)O₃ (RE³⁺ = La³⁺, Sm³⁺) perovskite compounds were synthesized by the conventional solid-state reaction route. Both solubility of rare earth in Ba(Zr_0.9Ti_0.1)O₃ and formation of perovskite structure with the Pm$\bar{3}$m space group were verified by the Rietveld method using X-ray diffraction data. SEM micrographs of all ceramics revealed high densification, low porosity, and even homogeneous grain distribution of various dimensions over the total surface. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of impedance, conductivity, modulus formalism, and charge carriers activation energy were used to explain the microstructure–electrical property relationships.

Undoped Ba(Zr_0.9Ti_0.1)O₃ and rare-earth-doped (Ba_1−xRE_2x/3)(Zr_0.9Ti_0.1)O₃ (RE³⁺ = La³⁺, Sm³⁺) perovskite compounds were synthesized by the conventional solid-state reaction route.     

Defect induced electrocatalytic hydrogen properties of pentagonal PdX2 (X = S,Se)

Searching for catalysts of hydrogen evolution reaction (HER) that can replace Pt is critical. Here, we investigated the HER electrocatalytic activity of pentagonal PdS₂ (penta-PdS₂) and PdSe₂ (penta-PdSe₂) by first-principles calculations. Three types of vacancies (V_S/Se, V_Pd, DV_S/Se) were constructed to activate the inert basal planes of PdS₂ and PdSe₂. The results show that S/Se and Pd vacancies significantly improve HER performance, and the Gibbs free energy (ΔG_H) of systems can be further regulated by vacancy concentration. Particularly, PdS₂ with 2.78% V_S, 50% V_Pd and PdSe₂ with 12.5% V_Se display the optimal ΔG_H value and the highest exchange current density. Further analysis of charge transfer and band structures were described that the introduce of vacancies efficiently regulates the electronic properties, resulting in the diminution of bandgap, and accelerates the charge transfer, thereby contributing to an enhanced electron environment for HER process. Our results provide a theoretical guidance for the applications of pentagonal transition-metal dichalcogenides as catalysts of hydrogen evolution reaction.

The HER electrocatalytic activity of pentagonal PdX₂ (X = S, Se) can significantly be improved by S/Se and Pd vacancies and can be further regulated by vacancy concentration.     

Mg–Ni–La based small hydrogen storage tank: kinetics,reversibility and reaction mechanisms

The improvement of de/rehydrogenation kinetics and reversibility of a Mg–Ni–La based small hydrogen storage tank by doping with TiF₄ and MWCNTs is reported for the first time. During sample preparation, MgH₂ milled with 20 wt% LaNi₅ and 5 wt% TiF₄ and MWCNTs produces Mg₂NiH₄ and LaH₃. Two-step dehydrogenation of Mg₂NiH₄ and MgH₂ is detected at 295 and 350 °C, respectively. Hydrogen desorption and absorption of the tank complete within 150 and 16 min, respectively, together with reversible hydrogen storage capacity up to 4.00 wt% H₂ (68% of theoretical value) upon 16 de/rehydrogenation cycles. Heat release from exothermic hydrogenation is removed effectively at the end of a double tube heat exchanger, where the reaction heat and heat transfer fluid are first in contact. Co-catalytic effects of Mg₂NiH₄ and LaH₃ as well as good hydrogen diffusion benefit dehydrogenation kinetics and reversibility of the tank.

De/hydrogenation performances and mechanisms of a Mg–Ni–La based H₂ storage tank are investigated for the first time.     

Investigation on the upconversion luminescence and ratiometric thermal sensing of SrWO4:Yb3+/RE3+ (RE = Ho/Er) phosphors

SrWO₄ phosphors doped with Ho³⁺(Er³⁺)/Yb³⁺ are successfully prepared by a high temperature solid-state reaction method. The upconversion (UC) luminescence properties of all the samples have been investigated under 980 nm excitation. Strong green emissions are obtained in the SrWO₄:Yb³⁺/Ho³⁺ and SrWO₄:Yb³⁺/Er³⁺ samples with the naked eyes. In a temperature range going from 303 K to 573 K, the UC emission spectra of the phosphors have been measured. Then the temperature sensing properties also have been discussed via fluorescence intensity ratio (FIR) technology. For the SrWO₄:Yb³⁺/Ho³⁺ phosphor, the FIR technologies based on thermal coupling levels (TCLs)(⁵F₄,⁵F₅) and non-thermal coupling levels (non-TCLs)(⁵S₂, ⁵F₄/⁵F₅) are used for investigating the sensitivity. The results show that the maximum absolute sensitivity reaches 0.0158 K⁻¹ with non-TCLs. As for Yb³⁺/Er³⁺ codoped SrWO₄ phosphor, the maximum absolute sensitivity reaches 0.013 K⁻¹ with TCLs (²H_11/2,⁴S_5/2) at a temperature of 513 K. These significant results demonstrate that the SrWO₄:Ho³⁺(Er³⁺)/Yb³⁺ phosphors are robust for optical temperature sensors.

SrWO₄ phosphors doped with Ho³⁺(Er³⁺)/Yb³⁺ are successfully prepared by a high temperature solid-state reaction method.     

Microstructure and local electrical behavior in [(Nd2Ti2O7)4/(SrTiO3)n]10 (n = 4–8) superlattices

Artificial [(Nd₂Ti₂O₇)₄/(SrTiO₃)_n]₁₀ superlattices (n = 4 and 8) were successfully epitaxially grown on SrTiO₃ substrates by pulsed laser deposition using the in situ high energy electron diffraction reflection diagnostic. The crystallographic relationships between Nd₂Ti₂O₇ (NTO) and SrTiO₃ (STO) (layers and substrate) were: [100]_NTO//[001]_STO, [010]_NTO//[$\bar{1}$10]_STO, and (00l)_NTO//(110)_STO. Nanoscale current variation was detected on both superlattices, with the (NTO₄/STO₄)₁₀ heterostructure showing a higher density. The (NTO₄/STO₄)₁₀ sample did not show a piezoelectric response when measured by piezo-force microscopy (PFM), while ambiguous piezoactivity was observed on the (NTO₄/STO₈)₁₀ superlattice. Scanning transmission electron microscopy energy dispersive spectroscopy analysis showed the diffusion of Nd³⁺ cations on Sr²⁺ sites in SrTiO₃ structure into the multilayers, which was more pronounced when the value of n was lower. These particular nanoscale electrical behaviors, evidenced by electrical conducting channels and misleading PFM signals, were mainly attributed to the presence of oxygen vacancies in the SrTiO₃ layers at higher concentrations near the interface and to the mixed valence state of the titanium (Ti³⁺/Ti⁴⁺). This work showed the strong influence of interface structure on nanoscale electrical phenomena in complex oxide superlattices.

Artificial [(Nd₂Ti₂O₇)₄/(SrTiO₃)_n]₁₀ superlattices were epitaxially grown. Local conductivity and misleading PFM signals were mainly attributed to the oxygen vacancies in the SrTiO₃ layers and to the mixed valence state of the titanium.     

Comparative photocatalytic activity of sol–gel derived rare earth metal (La,Nd, Sm and Dy)-doped ZnO photocatalysts for degradation of dyes

Rare earth metal doping into semiconductor oxides is considered to be an effective approach to enhance photocatalytic activity due to its ability to retard the electron–hole pair recombination upon excitation. Herein, we report the synthesis of different rare earth metal (La, Nd, Sm and Dy)-doped ZnO nanoparticles using a facile sol–gel route followed by evaluation of their photocatalytic activity by studying the degradation of methylene blue (MB) and Rhodamine B (RhB) under UV-light irradiation. Different standard analytical techniques were employed to investigate the microscopic structure and physiochemical properties of the prepared samples. The formation of the hexagonal wurtzite structure of ZnO was established by XRD and TEM analyses. In addition, the incorporation of rare earth metal into ZnO is confirmed by the shift of XRD planes towards lower theta values. All metal doped ZnO showed improved photocatalytic activity toward the degradation of MB, of which, Nd-doped ZnO showed the best activity with 98% degradation efficiency. In addition, mineralization of the dye was also observed, indicating 68% TOC removal in 180 min with Nd-doped ZnO nanoparticles. The influence of different operational parameters on the photodegradation of MB was also investigated and discussed in detail. Additionally, a possible photocatalytic mechanism for degradation of MB over Nd-doped ZnO nanoparticles has been proposed and involvement of hydroxyl radicals as reactive species is elucidated by radical trapping experiments.

In this study, we compared the photocatalytic activity of sol–gel derived rare earth metal (La, Nd, Sm and Dy)-doped ZnO photocatalysts by studying the degradation of MB and RhB under UV light irradiation.     

New ferromagnetic half-metallic perovskites for spintronic applications: BaMO3 (M = Mg and Ca)

Herein, first principles computer-based simulations were performed to predict the ground-state structure, mechanical stability, and magneto-electronic properties of BaMO₃ (M = Mg and Ca) perovskites, which have not been experimentally synthesized to date. Structural optimization authenticate the stability in the cubic structure for BaMO₃ perovskites having symmetry of the Pm3m space group. The tolerance factor and cohesive energy further validate the stability of BaMO₃ in the cubic phase. Moreover, mechanical stability was confirmed by the positive elastic constants, satisfying the necessary stability conditions. The band structure and density of states at the optimized lattice constants revealed the ferromagnetic half-metallic character of BaMO₃ materials, with O–p states playing a prominent role. The half-metallic character originates from the partial filling of the O–p states in the spin-down channel. Spatial charge distribution indicated the dominant ionic character of bonding. No change in the magnetic moment of perovskites was observed upon changing the M-site atoms. Various elastic parameters suggested that these perovskites are ductile in nature with highly anisotropic character. The three-dimensional graphical representation of different elastic moduli revealed that the linear compressibility is isotropic, whereas the shear modulus, Young''s modulus, and Poisson''s ratio of these perovskites are highly anisotropic. The results obtained in this study are in agreement with those reported in the literature for other similar perovskites.

Herein, first principles computer-based simulations were performed to predict the ground-state structure, mechanical stability, and magneto-electronic properties of BaMO₃ (M = Mg and Ca) perovskites, which have not been experimentally synthesized to date.     

Facile synthesis of Tb-decorated graphene oxide: electrochemical stability,hydrogen storage,and corrosion inhibition of Mg AZ13 alloy in 3.5% NaCl medium

Magnesium alloys have been broadly used due to their lightweight and high ductility. However, they are subject to corrosion which deteriorates their properties. To develop a novel corrosion inhibitor coating for Mg alloys, we performed functionalization of a graphene oxide (GO) matrix with Tb(iii) to improve the electrochemical behaviour and coating stability of a GO and Tb composite on the metal alloys in corrosive medium. The functionalized terbium GO material was characterized by microscopy, spectroscopy, and XRD techniques to confirm the non-covalent interactions on the active surface of the host material. The corrosion inhibition was found to be ca. 80% and electrochemical stability was observed to be high at a voltage of 900 mV. Computational studies also support the potential anti-corrosion applications of this material.

Terbium functionalized graphene oxide interacted with an Mg²⁺ surface by the active side of GO.     

Electronic and optical properties of two-dimensional heterostructures based on Janus XSSe (X = Mo,W) and Mg(OH)2: a first principles investigation

Two-dimensional (2D) materials have attracted numerous investigations after the discovery of graphene. 2D van der Waals (vdW) heterostructures are a new generation of layered materials, which can provide more desirable applications. In this study, the first principles calculation was implemented to study the heterostructures based on Janus TMDs (MoSSe and WSSe) and Mg(OH)₂ monolayers, which were constructed by vdW interactions. Both MoSSe/Mg(OH)₂ and WSSe/Mg(OH)₂ vdW heterostructures have thermal and dynamic stability. Besides, XSSe/Mg(OH)₂ (X = Mo, W) possesses a direct bandgap with a type-I band alignment, which provides promising applications for light-emitting devices. The charge density difference was investigated, and 0.003 (or 0.0042) |e| were transferred from MoSSe (or WSSe) layer to Mg(OH)₂ layer, and the potential drops were calculated to be 11.59 and 11.44 eV across the interface of the MoSSe/Mg(OH)₂ and WSSe/Mg(OH)₂ vdW heterostructures, respectively. Furthermore, the MoSSe/Mg(OH)₂ and WSSe/Mg(OH)₂ vdW heterostructures have excellent optical absorption wave. Our studies exhibit an effective method to construct new heterostructures based on Janus TMDs and develop their applications for future light emitting devices.

Two-dimensional (2D) materials have attracted numerous investigations after the discovery of graphene.     

Anomalous behavior above the Curie temperature in (Nd1−xGdx)0.55Sr0.45MnO3 (x = 0, 0.1, 0.3 and 0.5)

Magnetic properties were studied just above the ferromagnetic–paramagnetic (FM–PM) phase transition of (Nd_1−xGd_x)_0.55Sr_0.45MnO₃ with x = 0, 0.1, 0.3 and 0.5. The low-field inverse susceptibility (χ⁻¹) of Nd_0.55Sr_0.45MnO₃ exhibits a Curie–Weiss-PM behavior. For x ≥ 0.1, we observe a deviation in χ⁻¹(T) behavior from the Curie–Weiss law. The anomalous behavior of the χ⁻¹(T) was qualified as Griffiths phase (GP)-like. The study of the evolution of the GP through a susceptibility exponent, the GP temperature and the temperature range of the GP reveals that the origin of the GP is primary due to the accommodated strain. Likewise, the magnetic data reveal distinct features visible only for x = 0.5 at a low magnetic field that can be qualitatively understood as the result of ferromagnetic polarons, entailed by the strong effect of chemical/structural disorder, whose concentration increases upon cooling towards the Curie temperature. We explained the magnetic properties at a high temperature for the heavily Gd-doped sample (x = 0.5) within the phase-separation scenario as an assembly of ferromagnetic nanodomains, antiferromagnetically coupled by correlated Jahn–Teller polarons.

Magnetic properties were studied just above the ferromagnetic–paramagnetic (FM–PM) phase transition of (Nd_1−xGd_x)_0.55Sr_0.45MnO₃ with x = 0, 0.1, 0.3 and 0.5.     

A case study of Fe2TaZ (Z = Al,Ga, In) Heusler alloys: hunt for half-metallic behavior and thermoelectricity

We have computed the electronic structure and transport properties of Fe₂TaZ (Z = Al, Ga, In) alloys by the full-potential linearized augmented plane wave (FPLAPW) method. The magnetic conduct in accordance with the Slater–Pauling rule classifies them as non-magnetic alloys with total zero magnetic moment. The semiconducting band profile and the density of states in the post DFT treatment are used to estimate the relations among various transport parameters such as Seebeck coefficient, electrical conductivity, thermal conductivity, and figure of merit. The Seebeck coefficient variation and band profiles describe the p-type behavior of charge carriers. The electrical and thermal conductivity plots follow the semiconducting nature of bands along the Fermi level. The overall measurements show that semi-classical Boltzmann transport theory has well-behaved potential in predicting the transport properties of such functional materials, which may find the possibility of their experimental synthesis for future applications in thermoelectric technologies.

Crystal structure in conventional unit cell for Fe₂TaZ (Z = Al, Ga, In) in Fm$\bar{3}$m configuration.     

Reduction and oxidation kinetics of NiWO4 as an oxygen carrier for hydrogen storage by a chemical looping process

NiWO₄ with a volumetric storage density (VSD) of 496 g L⁻¹ was studied to evaluate its H₂ storage potential as an oxygen carrier under a chemical looping (CL) process scheme. The material was synthesized by precipitation and calcined at 950 °C for 5 hours in air. Characterization consisted in XRD, BET surface area, SEM and EDS analysis. NiWO₄ hydrogen storage reduction-oxidation evaluation was performed by TGA using 5% v H₂/Ar and 2.2% v H₂O/Ar at 800 °C. Global kinetics for the reduction step was studied from 730 to 870 °C using 2 to 5% v of H₂/Ar. While oxidation kinetics was examined from 730 to 870 °C using 0.8 to 2.2% v H₂O/Ar. A hydrogen storage multicycle stability test was performed by exposing NiWO₄ to 17 consecutive redox cycles. XRD results of the synthesized material indicate NiWO₄ as the only crystalline phase. Fully reduced material found only W and Ni species, while reoxidation led back to NiWO₄. BET surface area of synthesized material was 4.25 m² g⁻¹. SEM results showed fresh NiWO₄ composed of non-porous large particles (1–5 μm). After reduction, the material shown a porous coral-like morphology with particles between 50 to 100 nm. EDS analysis results confirmed the compositions of the reduced (Ni + W) and fully oxidized NiWO₄ species, respectively. Oxygen carrier reaction conversions for both reduction and regeneration steps were 100%. Global kinetic studies indicate a first order reaction for the two reduction steps and during oxidation, with activation energies of 22.1, 48.4 and 53.4 kJ mol⁻¹ for the two reduction and oxidation steps, respectively. NiWO₄ multicycle stability test shown no loss of VSD and fast reduction and oxidation kinetics under the studied conditions after seventeen consecutive redox cycles, which confirms the potential of this material with respect to current oxygen carriers reported in the literature for hydrogen storage applications.

H₂ storage of NiWO₄ with a volumetric storage density of 496 g L⁻¹ was studied and evaluated under a chemical looping reaction scheme by TGA. Results confirms the high potential of NiWO₄ to current oxygen carriers reported in the literature.     

Microstructure and corrosion behavior of Al95−xNixY5 (x = 7,10) glassy ribbons

In this work, we correlate the microstructure and passivation of the Al_95−xNi_xY₅ lightweight glassy ribbons (x = 7 and 10) using various techniques. The overdosed Ni (x = 10) can increase the melt viscosity and then deteriorate its glass-forming ability (GFA), ribbon formability, and Y-depleted extra layer formation. Consequently, the overdosed Ni weakens the passivation stability and corrosion resistance of the as-spun ribbon. The key role of the overdosed Ni can form a strong network and crystalline grain boundary in the amorphous matrix, which can transport Y and O to participate in the oxidation. These results can help us explore a valuable method for designing new Al-based metallic glasses.

The Al_95−xNi_xY₅ ribbon x = 7 has a Y-depleted extra film and has a longer passive zone in the polarization curve and higher corrosion resistance than x = 10.