Ta Compounds Research Articles

Dazzling red-emitting Ca2EuMO6 (M = Sb, Nb, Ta) double-perovskite phosphors with potential application in phosphor-converted white light-emitting diodes

In this paper, three new efficient Eu3+-activated Ca2EuMO6 (M = Sb, Nb, and Ta) red-emitting phosphors with outstanding luminescence properties were prepared by using the high-temperature solid-state reaction method. X-ray diffraction and Rietveld refinements revealed the double-perovskite structure of Ca2EuMO6 (M = Sb, Nb, and Ta) compounds. Photoluminescent excitation and emission spectra, decay lifetimes, CIE chromaticity coordinates, color purity values, internal quantum efficiency, and thermal stability were discussed in detail. Under the excitation of 395 nm near-ultraviolet light, these Ca2EuMO6 (M = Sb, Nb, and Ta) phosphors demonstrated bright narrow-band red emissions with peaks at 592, 620, 656, and 703 nm due to the 5D0→7FJ (J = 1–4) transitions of Eu3+ ions. The internal quantum efficiencies of the Ca2EuSbO6, Ca2EuNbO6, and Ca2EuTaO6 samples were determined to be 39.3%, 41.6%, and 40.4%, respectively. Impressively, the emission intensity of Ca2EuNbO6 is about 1.25 times higher than that of commercial Y2O3:Eu3+ red phosphor. CIE color coordinates of Ca2EuMO6 (M = Sb, Nb, and Ta) phosphors were calculated to be (0.6748, 0.3250), (0.6800, 0.3198), and (0.6790, 0.3208), respectively; along with high color purity of 90.7%, 93.2%, and 92.7%. Besides, their thermal stability was also investigated, and the corresponding emission intensities of Ca2EuMO6 (M = Sb, Nb, and Ta) at 423 K were respectively maintained at 73%, 86%, and 80% of that at 303 K. All results show that these newly developed red-emitting Ca2EuMO6 (M = Sb, Nb, and Ta) phosphors possess potential applications in white light-emitting diodes.

Comprehensive first principles to investigate optoelectronic and transport phenomenon of lead-free double perovskites Ba2AsBO6 (B[dbnd]Nb, Ta) compounds

In the current work we studied the structural, elastics, electrical, optical, thermoelectric, as well as spectroscopic limited maximum efficiency (SLME) of oxide based Ba2AsBO6 (BNb, Ta) materials. All the calculations were performed using first-principles calculation by employing the WIEN2k code. We checked the stability in diverse forms such as optimization, phonon dispersion, mechanical, formation energy, cohesive energy, and thermal stability is computed. The semiconducting nature of these Ba2AsBO6 (BNb, Ta) systems is revealed by calculating the direct band gap values are 1.97 eV and 1.49 eV respectively. Additionally, we determined the optical properties which analyze the utmost absorption and transition of carriers versus photon energy (eV). Moreover, Ba2AsNbO6 has an estimated SLME of 32 %, making it an encouraging alternative for single-junction solar cells. Lastly, we studied the transport properties against temperature, the chemical potential for p-type and n-type charge carriers at various temperatures. At 300 K, the zT values are found to be 0.757 and 0.751 for Ba2AsBO6 (BNb, Ta) compounds respectively. Both materials were examined as having strong absorption patterns and an excellent figure of merit (ZT), indicating that materials are appropriate for daily life applications.

Effects of solvent casted poly (lactic acid)/poly(ethylene glycol)/paraben derivative triazine films on antibacterial performance and cytotoxicity

AbstractA series of poly(lactic acid) (PLA) films that including fully paraben substituted triazine derivatives having anti‐bacterial properties have been prepared by utilizing the solvent‐casting method. PLA as biodegradable polymer, poly(ethylene glycol) (PEG) as a plasticizing agent and s‐triazine molecules (TA01, TA02, TA03, TA04, and TA05) behaving as an anti‐bacterial component have been utilized in the experiments. The influence of TA compounds on the antibacterial performance of PLA/PEG films was investigated for the first time against Gram‐negative Escherichia coli (E. coli) and Gram‐positive Staphylococcus aureus (S. aureus) bacteria via the contact active method. TA01‐03‐05 incorporated PLA/PEG films gave the best results against E.coli bacteria and log10 reductions of these films were 0.78, 0.64, and 0.65 respectively. The effect of TA compounds on the cell viability was investigated against cancer and non‐cancerous cell lines using an MTS assay. The results showed that TA compounds had a positive effect on cell growth in non‐cancerous cells, while they had a negative effect on cell growth in cancer cells. Furthermore, the addition of TA considerably increased the decomposition temperatures from 349° to 361° and char yield from 0.65 for PLA/PEG film to 2.3 for PLA/PEG/TA05. All of the films had good transparency and low opacity which was 7.2 for pure PLA used for control and the maximum opacity value was 11.2 observed for PLA/PEG/01. TA03 and TA04 caused a decrement of water vapor permission when compared to PLA/PEG films from 1439 to 749 and 664. It was also observed that pure PLA/PEG film lost weight rapidly over time during degradation tests. On the other hand, weight loss wasn't observed in PLA/PEG/TA films. This study focused on demonstrating the use of our new, flexible PLA/PEG derivatives in food and medical packaging.

Phase stability and thermo-physical properties of Laves-Co<sub>2</sub>(Hf Ta) alloys

There exists still the controversy over the stable structure of Laves-phase Co<sub>2</sub>(Hf Ta) alloys with the C14, C15 or C36 structures. In this study, the stability, electronic and thermodynamic properties of Laves-phase Co<sub>2</sub>(Hf Ta) are investigated. In order to fully understand the influence of magnetic state and temperature on phase stability, we systematically study the free energy change at finite temperature, elastic stability, and phonon dispersion. The low Curie temperature can be estimated, which suggests that the Co<sub>2</sub>(Hf Ta) alloys possess the paramagnetic state in a wide temperature range. Results indicate that the lattice vibration and electronic excitation have an important effect on the phase stability. The ground state of Co<sub>2</sub>Hf compound has a C14-type structure, while the ground state of Co<sub>2</sub>Ta has a C36-type structure, without the effect of temperature. After doping Hf with different concentrations (0.25, 0.50, 0.75) into Co<sub>2</sub>Ta, the most stable structure still possesses the C36-type structure. After considering the contribution of vibration entropy and electron entropy, the relatively stable structures of Co<sub>2</sub>Hf and Co<sub>2</sub>Ta undergo the C36 and C14 phase transition, respectively. In addition, the thermodynamic properties, including Debye temperature, heat capacity, and vibration entropy, which vary with pressure and temperature, are studied. The electronic properties of Co<sub>2</sub>Hf and Co<sub>2</sub>Ta compounds are analyzed by the charge difference and density of states. The similar electronic density of states between different phases suggest that the Lave phases have the similar stability. The Hf-Co bonding with a certain direction is revealed. Our results are of great significance in understanding the structure and properties of Co<sub>2</sub>Hf and Co<sub>2</sub>Ta compounds.

Structural Modeling of O/F Correlated Disorder in TaOF3 and NbOF3-x(OH)x by Coupling Solid-State NMR and DFT Calculations.

The structure of MOF3 (M = Nb, Ta) compounds was precisely modeled by combining powder X-ray diffraction, solid-state NMR spectroscopy, and semiempirical dispersion-corrected DFT calculations. It consists of stacked ∞(MOF3) layers along the c⃗ direction formed by heteroleptic corner-connected MX6 (X = O, F) octahedra. 19F NMR resonance assignments and occupancy rates of the anionic crystallographic sites have been revised. The bridging site is shared equally by the anions, and the terminal site is occupied by F only. An O/F correlated disorder is expected since cis-MO2F4 octahedra are favored, resulting in one-dimensional -F-M-O-M- strings along the <100> and <010> directions. Ten different 2 × 2 × 1 supercells per compound, fulfilling these characteristics, were built. Using DFT calculations and the GIPAW approach, the supercells were relaxed and the 19F isotropic chemical shift values were determined. The agreement between the experimental and calculated 19F spectra is excellent for TaOF3. The 1H and 19F experimental NMR spectra revealed that some of the bridging F atoms are substituted by OH groups, especially in NbOF3. New supercells involving OH groups were generated. Remarkably, the best agreement is obtained for the supercells with the composition closest to that estimated from the 19F NMR spectra, i.e., NbOF2.85(OH)0.15.

Elastic anisotropy, thermal conductivity and tensile properties of MAX phase V2GaC, Nb2GaC and Ta2GaC: First-principles calculations

MAX phase series materials have excellent thermal, electrical and mechanical properties, and have great research potential. In this work, the structural characteristics, elastic anisotropy, thermal and phonon properties of hexagonal M2GaC (M = V, Nb and Ta) compounds were calculated using the first-principle calculation method. The stress-strain method and Voigt-Reuss-Hill approximation are used to determine the elastic properties of single crystals and polycrystals, respectively. By calculating the formation enthalpy, it is found that M2GaC compounds are stable. Meanwhile, these M2GaC are brittle materials with respect to Poisson's ratio, GH/BH and Cauchy pressure. The elastic anisotropy of M2GaC is illustrated by the elastic anisotropy index, three-dimension (3D) surface configuration and two-dimension (2D) projection, the order of elastic anisotropy is Nb2GaC > Ta2GaC > V2GaC. Finally, the sound velocity, Debye temperature, thermal conductivity and anisotropy are discussed to provide theoretical support for further study of MAX phase compounds.

Tantalum Extraction and Its Wide-Ranging Significance

Tantalum is a transition metal with atomic number 73. It has a shiny, silvery-gray appearance and offers a distinctive set of characteristics that give it significant value in a range of applications. Tin is commonly found in association with niobium (Nb) and tantalum (Ta). Cassiterite (SnO2) is the primary tin mineral, typically containing substantial quantities of both niobium (Nb) and tantalum (Ta) compounds. A significant portion of these components are left behind in the slag that is produced at the end of the industrial process, which occurs during the extraction and refining stages of the tin manufacturing process. Those slags are already capable of being considered as a potential and significant source of refractory metals such as tantalum and niobium due to their potential. The mining sector is vital to the nation's gross domestic product (GDP), and tantalum is an important component of that industry. The extraordinary element tantalum is discussed in this abstract, along with its extraction, important properties, and many applications

The Physiological Responses of Wheat and Maize Seedlings Grown under Water Deficit Are Modulated by Pre-Application of Auxin-Type Plant Growth Regulators.

The physiological responses of wheat and maize seedlings to exogenous auxin-type compounds 1-[2-chloroethoxycarbonyl-methyl]-4-naphthalenesulfonic acid calcium salt (TA-12) and 1-[2-dimethylaminoethoxicarbonylmethyl]naphthalene chlormethylate (TA-14) application prior to polyethyleneglycol-6000 (PEG) treatment were studied. PEG treatment inhibited seedlings growth and caused alterations in their antioxidant defence which was crop-specific. PEG increased the non-enzymatic antioxidants along with inhibition of enzymatic antioxidant activity in wheat, while in maize the opposite effects were found. The TA-12 and TA-14 applied alone increased most of the growth parameters measured in both crops, as well as the catalase activity and protein content of wheat. The growth of PEG-treated wheat and maize plants was improved by foliar spray with TA-compounds (TAs). Application of TAs before PEG treatment maintained low-molecular weight thiol-containing compounds and protein contents, and catalase and peroxidase activities close to the control levels. This was better expressed in maize than in wheat seedlings. The results showed that the preliminary application of TA-12 and TA-14 can reduce the adverse effects of moderate water deficit by crop-specific adjustment of the antioxidant defence to counteract stress.

Syntheses of Group 5 Amide Amidinates and Their Reactions with Water: Different Reactivities of Nb(V) and Ta(V) Complexes.

Chemistries of Nb(V) and Ta(V) compounds are essentially identical as a result of lanthanide contraction. Hydrolysis of M(NMe2)5 (M = Nb, Ta), for example, yields [M(μ3-O)(NMe2)3]4 (M = Nb, 1; Ta, 2) reported earlier. The similar reactivities of Nb(V) and Ta(V) compounds make it challenging, for example, to separate the two metals from their minerals. We have found that the reactions of H2O with amide amidinates M(NMe2)4[MeC(NiPr)2] (M = Nb, 3; Ta, 4) show that the niobium and tantalum analogues take different principal paths. For the Nb(V) complex 3, the amidinate and one amide ligand are liberated upon treatment with water, yielding [Nb(μ3-O)(NMe2)3]4 (1). For the Ta(V) complex 4, the amide ligands are released in the reaction with H2O, leaving the amidinate ligand intact. [Ta(μ3-O)(NMe2)3]4 (2), the analogue of 1, was not observed as a product in the reaction of 4 with H2O. To our knowledge, this is the first example of the formation of two different complexes that maintain the (V) oxidation state in both metals. The new complexes M(NMe2)4[MeC(NiPr)2] (M = Nb, 3; Ta, 4) have been prepared by the aminolysis of M(NMe2)5 (M = Nb, Ta) with iPrN(H)C(Me)=NiPr (5). The hydrolysis of 3 and 4 has been investigated by DFT electronic structure calculations. The first step in each hydrolysis reaction involves the formation of a hydrogen-bonded complex that facilitates a proton transfer to the amidinate ligand in 3 and protonation of an axial dimethylamide ligand in 4. Both proton transfers furnish an intermediate metal-hydroxide species. The atomic charges in 3 and 4 have been computed by Natural Population Analysis (NPA), and these data are discussed relative to which of the ancillary ligands is protonated initially in the hydrolysis sequence. Ligand exchanges in 3 and 4 as well as the exchange in iPrN(H)C(Me)=NiPr (5) were probed by EXSY NMR spectroscopy, giving rate constants of the exchanges: 0.430(13) s-1 (3), 0.033(6) s-1 (4), and 2.23(7) s-1 (5), showing that the rate of the Nb complex Nb(NMe2)4[MeC(NiPr)2] (3) is 13 times faster than that of its Ta analogue 4.

Tribo-Oxidation and Tribological Behavior of TaC–20%SiC Composites at Elevated Temperatures

Abstract Tribo-oxidation mechanism and tribological behavior of TaC–20 vol%SiC composites from 25 to 800 °C coupled with aluminum oxide (Al2O3) and cemented carbide (WC–Co) were investigated. Tribo-oxidation products on the worn surface were analyzed by X-ray photoelectron spectroscopy (XPS). The results showed that as temperature increased from 25 °C to 800 °C, the specific wear-rates (WRs) of the composites decreased from 10−3 mm3N−1m−1 to 10−4 mm3N−1m−1 when coupled with Al2O3, while the WRs increased from 10−6 mm3N−1m−1 to 10−3 mm3N−1m−1 continuously when coupled with WC–Co. At 25 °C, TaC in the composite was partially oxidized into TaO2 as coupled with the two dualities. At 400 °C, the TaC in composite was oxidized into Ta2O5, while SiC was oxidized into SiCOx as coupled with Al2O3, while they were oxidized into Ta2O5 and SiO2−x as coupled with WC–Co. At 800 °C, the composites were oxidized into Ta2O5, SiCOx, and SiO2−x as coupled with the two dualities. The segregation of Ta compounds on the surface was promoted by friction. For the composites–Al2O3 tribo-pair, the wear mechanism changed from abrasion and adhesion at low temperature, to abrasion, adhesion, and tribochemical reaction (oxidation) at medium temperature, and adhesion and tribochemical reaction at high temperature. For composites–WC–Co tribo-pair, the wear mechanism was adhesion and tribochemical reaction in the whole temperature range.

Magnetodielectric effect and significant magnetoelectric coupling of Co3NiNb2O9 single crystal

A4B2O9 (A = Co, Fe, Mn, Ni, B = Nb, Ta) compounds with a corundum-type structure can host multiferroic phenomena and present magnetoelectric coupling to achieve manipulations of their ground states by external fields. High quality Ni-doped Co4Nb2O9 single crystals of Co3NiNb2O9 have been synthesized for the first time using optical floating zone technique. Co3NiNb2O9 exhibits an antiferromagnetic order at 32 K with an easy magnetization axis in the ab plane. Field-dependent magnetizations at 20 K along [100] and [120] directions have a slope change at 6 and 9 kOe, respectively, indicating a spin-flop transition or spin rotation in the ab plane. Temperature dependence of dielectric constants along [100] and [120] directions show a magnetic-field-induced peak near the antiferromagnetic transition, proving a sizable magnetodielectric effect. Pyroelectric currents along [100] and [120] directions also have a divergent behavior near the transition under magnetic fields, manifesting a magnetoelectric coupling effect. The electric polarization along [120] direction reaches 128 μC/m2 under a magnetic field of 40 kOe, larger than that in most phases of the A4B2O9 system.

Electron–phonon coupling of the Ti3Sb compound

Using the first-principles method based on density functional theory, we investigate the electronic, mechanical, phononic, superconducting, and topological properties of the A15 superconductor Ti3Sb with/without the inclusion of spin–orbit coupling (SOC). We find that the calculated elastic constants satisfy the Born stability criteria and the ductile nature of Ti3Sb. The result of phonon calculations reveals that the Pm3¯n structure is dynamically stable. Sb atoms are dominated in the low-frequency region due to the mass difference between Ti and Sb from partial phonon calculations. Our electronic structure calculations show that Ti3Sb has metallic band structures with Ti-d bands near the Fermi energy. The electron–phonon coupling constant (λ≃0.80) indicates that Ti3Sb has strong electron–phonon coupling. The critical temperature (Tcμ⋆=0.10) is found to be 6.24 and 6.56 K with and without the SOC effect, respectively. Due to Ti’s relatively small SOC strength, we do not find evidence of non-trivial topology in contrast to Ta compounds such as Ta3Sb.

Equiatomic quaternary CoXCrAl (X = V, Nb, and Ta) Heusler compounds: Insights from DFT calculations

The half-metallic ferromagnets are likely materials to the spintronics systems for the next generation electronic devices. Among the half-metallic ferromagnetic materials, the equiatomic quaternary Heusler (EQH) compounds get great attention in the recent times. In this study, the EQH CoXCrAl (X = V, Nb, and Ta) compounds are investigated using Density Functional Theory (DFT). The three structural types as type-I, type-II, and type-III, are considered to determine the most stable structural types of CoXCrAl compounds. Furthermore, the three magnetic configurations as paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM), are studied to find out the most stable magnetic configuration. The type-I FM configuration is the most stable configuration for the CoXCrAl compounds. The calculated electronic band structures reveal that the CoXCrAl compounds are half-metals with metallic behavior in spin-up channel and semiconducting behavior in spin-down channel. Also, the possible d-d hybridizations between the Co, X, and Cr atoms are investigated to show the half-metallic character in detail. Furthermore, the calculated elastic constants satisfy the Born stability criteria, then the CoXCrAl compounds have mechanical stability. Using the determined constants, the mechanical properties are obtained for CoXCrAl compounds. In addition, the dynamical properties are studied and it is found that CoXCrAl compounds are dynamically stable. The structural, magnetic, electronic, mechanic and dynamical properties of CoXCrAl compounds that are the potential candidates for the spintronics applications are presented in this study.

First-principle investigation on the thermoelectric properties of XCoGe (X = V, Nb, and Ta) half-Heusler compounds

Half-Heusler compound is a promising thermoelectric material due to its excellent conversion performance. In this study, we investigate the electronic structure, and thermoelectric properties of XCoGe (X = V, Nb, and Ta) compounds based on density functional theory. Combining the semi-classical Boltzmann transport equation and the deformation potential theory, the thermoelectric properties such as Seebeck coefficient, relaxation time, electrical conductivity, power factor, electronic thermal conductivity, and lattice thermal conductivity are analyzed. The NbCoGe compound possesses a large dimensionless figure of merit, which is related to the large electrical conductivity, small effective mass, and large relaxation time. The ZT values of n- and p-type NbCoGe compounds reach 1.6 and 1.3 at T = 1200 K, respectively. These findings will provide valuable guidance for exploring half-Heusler compounds with high thermoelectric performance.

Ab-initio investigations for structural, mechanical, optoelectronic, and thermoelectric properties of Ba2SbXO6 (X[dbnd]Nb, Ta) compounds

We report the structural, mechanical, electronic, optical, thermoelectric properties and spectroscopic limited maximum efficiency (SLME) of oxide double perovskite structure Ba2SbNbO6 and Ba2SbTaO6 compounds. All the investigations were performed through the first-principles density functional theory (DFT). The results obtained for the elastic constants affirms the mechanical stability of the studied double perovskite compounds. The calculated data of bulk modulus (B), shear modulus (G), and Young's modulus (E) for Ba2SbTaO6 are found to be greater than those of Ba2SbNbO6. The obtained ratio of Bulk to shear modulus (B/G) shows that Ba2SbNbO6 and Ba2SbTaO6 are ductile in nature and are suitable for the device fabrications. The electronic properties of studied compounds are explained in terms of their energy bands, total and partial density of states. The computed electronic band structure reveals the direct band gap semiconducting nature of both compounds. The energy dependent optical properties such as, dielectric tensor, optical conductivity, absorption, reflectivity, refraction and energy loss for both the studied compounds are investigated and are explained in order to highlight the potential of studied compounds for the photovoltaic applications. In addition to electronic and optical properties, we have also studied the electron relaxation time-dependent thermoelectric properties, such as Seebeck coefficient, electronic thermal conductivity, electrical conductivity, thermoelectric power factor, and the thermoelectric figure of merit as a function of chemical potential at various temperatures for p-type and n-type charge carriers. The high absorption spectra and good thermoelectric figure of merit reveal that both the studied compounds, Ba2SbXO6 (X = Nb, Ta) are promising materials for photovoltaic and thermoelectric applications. The calculated SLME of 26.8% reveals that Ba2SbNbO6 is an appealing candidate for single-junction solar cells.

Photochemistry with Chlorine Trifluoride: Syntheses and Characterization of Difluorooxychloronium(V) Hexafluorido(non)metallates(V), [ClOF2 ][MF6 ] (M=V, Nb, Ta, Ru, Os, Ir, P, Sb).

A photochemical route to salts consisting of difluorooxychloronium(V) cations, [ClOF2]+, and hexafluorido(non)metallate(V) anions, [MF6]− (M=V, Nb, Ta, Ru, Os, Ir, P, Sb) is presented. As starting materials, either metals, oxygen and ClF3 or oxides and ClF3 are used. The prepared compounds were characterized by single‐crystal X‐ray diffraction and Raman spectroscopy. The crystal structures of [ClOF2][MF6] (M=V, Ru, Os, Ir, P, Sb) are layer structures that are isotypic with the previously reported compound [ClOF2][AsF6], whereas for M=Nb and Ta, similar crystal structures with a different stacking variant of the layers are observed. Additionally, partial or full O/F disorder within the [ClOF2]+ cations of the Nb and Ta compounds occurs. In all compounds reported here, a trigonal pyramidal [ClOF2]+ cation with three additional Cl⋅⋅⋅F contacts to neighboring [MF6]− anions is observed, resulting in a pseudo‐octahedral coordination sphere around the Cl atom. The Cl−F and Cl−O bond lengths of the [ClOF2]+ cations seem to correlate with the effective ionic radii of the M V ions. Quantum‐chemical, solid‐state calculations well reproduce the experimental Raman spectra and show, as do quantum‐chemical gas phase calculations, that the secondary Cl⋅⋅⋅F interactions are ionic in nature. However, both solid‐state and gas‐phase quantum‐chemical calculations fail to reproduce the increases in the Cl−O bond lengths with increasing effective ionic radius of M in [MF6]− and the Cl−O Raman shifts also do not generally follow this trend.

211-MAX borides: The stable boron-substituted 211-MAX compounds by first-principles

Applying the first-principles density functional pseudopotential plane-wave calculations, the energetic, mechanical, and dynamic stabilities of boron-substituted M2AlB (M=Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, Tc, Ru, Hf, Ta, W, Re, Os, Ir, Pt, Ag, and Au) compounds as the members of 211-MAX borides with Cr2AlC-type crystal structure were investigated. After well-converged geometry optimizations, the cohesive energy, formation enthalpy, single-crystal elastic constants, and phonon dispersion curves were calculated to explain the stabilities of the compounds. Except for M=Y, Ag, and Au compounds, the others are thermodynamically stable due to the negative formation enthalpies. M=Sc, Y, Zr, Hf, Os, Ir, and Pt compounds are dynamically unstable because of the negative phonon frequencies, and M=Ag and Au compounds are mechanically unstable. Beyond the detailed stability analysis, the structural, elastic, and mechanical properties, anisotropy factors, exfoliation states, and specifically hardness nature of the stable compounds were examined. A new modified hardness method, which includes the metallicity, is proposed to characterize the softness nature of MAX-phases. The relevant quantities, such as bond electronegativity, ionicity, and metallicity, were debated. The presented data were compared with available theoretical and experimental literature.

A new series of low-loss multicomponent oxide microwave dielectrics with a rock salt structure: Li5MgABO8 (A=Ti, Sn; B=Nb, Ta)

In this study, a series of Li5MgABO8 (A=Ti, Sn; B=Nb, Ta) compounds were designed and synthesized through a solid-state reaction method. The XRD patterns showed that a single phase was formed for all the samples. All the peaks were indexed based on the MgO-Like rock salt cubic structure with space group Fm-3m (225) and the peaks indicated that crystals presented different (111) orientation growths in the prepared samples. For all the specimens, the relative density values of 94% and above could be achieved when the sintering temperature exceeded 1300 °C. The εr values of the specimens showed an increasing trend when the sintering temperatures increased. However, the Q × f values firstly increased and then decreased with the rising temperatures. The electronically-induced strains and lattice-induced strains, which were evaluated by the bond strain index (BSI) and global instability index (GII), presented same variation trends as the Q × f values when the sintering temperature increased. The lowest dielectric loss was achieved in Li5MgTiNbO8 ceramics: εr=17.55, Q × f=109,700 GHz (f=7.379 GHz), τf =-32.5 ppm/°C, when sintered at 1290 °C for 4 h.

A first principles investigation on the influence of transition-metal elements on the structural, mechanical, and anisotropic properties of CaM2Al20 intermetallics

The anisotropy in elasticity, mechanical properties and electronic properties of CaM2Al20 (M = V, Nb, Cr, Ti, Mo and Ta) compounds were investigated using the first-principle calculations. These ternary compounds are structurally stable according to the obtained phonon frequencies and formation enthalpy. The results of elastic modulus, hardness and elastic constants explain that CaM2Al20 intermetallics have higher hardness and better resistance to deformation change than pure aluminum. Poisson’s ratio and the values of B/G confirm that CaTi2Al20, CaV2Al20, CaCr2Al20, CaNb2Al20 and CaTa2Al20 are brittle materials, but CaMo2Al20 is ductile material. The 3D surfaces of Young’s modulus and anisotropic constants confirm that CaMo2Al20 and CaTi2Al20 have the larger anisotropy than other four compounds. What’s more, the density of states and charge density differences of CaM2Al20 compounds explain the mechanism of the structural stability and mechanical properties.

Promising spintronics: Mn-based Heusler alloys Mn3Ga, Mn2YGa (Y = V, Nb, Ta), ScMnVGa

High spin-polarized materials are expected for the development of spintronic devices. In this work, we are aiming to find new spintronic materials in Mn-based binary, ternary and quaternary Heusler alloys by using the first-principles calculations. We investigated structures, electronic properties, magnetic, tetragonal distortion and mechanic properties of Mn3Ga, Mn2YGa (Y = V, Nb, Ta) and ScMnVGa. The results show that Mn3Ga, ScMnVGa type-I, and type-II have lower energy in antiferromagnetic (AFM) states than ferromagnetic (FM) and paramagnetic (NM). Mn2YGa (Y = V, Nb, Ta) compounds are more stable in FM states. The results of electronic and magnetic properties indicate that Mn3Ga is a gapless half-metallic antiferromagnet (Gapless HM-AFM). Mn2VGa and Mn2NbGa belong to gapless half-metallic ferrimagnets (Gapless HM-FE). Mn2TaGa is ferrimagnets. ScMnVGa type-I is half-metallic antiferromagnets (HM-AFM) and type-II belongs to spin gapless semiconductors with AFM (SGSs-AFM). Inspired by Ferromagnetic shape memory alloys (FAMAs), we performed tetragonal deformation of those compounds, and we predicted that Mn3Ga, Mn2YGa (Y = V, Nb, Ta) have possible martensitic transformations. Finally, the mechanical stability and elastic properties of above-mentioned in both cubic and tetragonal structures were discussed in detail.