Synthesis and Physical Properties of Iridium-Based Sulfide Ca1−xIr4S6(S2) [x = 0.23–0.33]

We present the synthesis and characterization of the iridium-based sulfide Ca1−xIr4S6(S2). Quality and phase analysis were conducted by means of energy-dispersive X-ray spectroscopy (EDXS) and powder X-ray diffraction (XRD) techniques. Structure analysis reveals a monoclinic symmetry with the space group C 1 2/m 1 (No. 12), with the lattice constants a = 15.030 (3) Å, b = 3.5747 (5) Å and c = 10.4572 (18) Å. Both X-ray diffraction and EDXS suggest an off-stoichiometry of calcium, leading to the empirical composition Ca1−xIr4.0S6(S2) [x = 0.23–0.33]. Transport measurements show metallic behavior of the compound in the whole range of measured temperatures. Magnetic measurements down to 1.8 K show no long range order, and Curie–Weiss analysis yields θCW = −31.4 K, suggesting that the compound undergoes a magnetic state with short range magnetic correlations. We supplement our study with calculations of the band structure in the framework of the density functional theory.

Dissipation-driven strange metal behavior

Anomalous metallic properties are often observed in the proximity of quantum critical points, with violation of the Fermi Liquid paradigm. We propose a scenario where, near the quantum critical point, dynamical fluctuations of the order parameter with finite correlation length mediate a nearly isotropic scattering among the quasiparticles over the entire Fermi surface. This scattering produces a strange metallic behavior, which is extended to the lowest temperatures by an increase of the damping of the fluctuations. We phenomenologically identify one single parameter ruling this increasing damping when the temperature decreases, accounting for both the linear-in-temperature resistivity and the seemingly divergent specific heat observed, e.g., in high-temperature superconducting cuprates and some heavy-fermion metals.

First-principles investigations of the half-metallic ferromagnetic LaCoTiIn equiatomic quaternary Heusler alloy for spintronics

We have evaluated the structural and mechanical stability, electronic structure, total spin magnetic moment, and Curie temperature of LaCoTiIn Equiatomic Quaternary Heusler Alloy (EQHA) using first-principles studies. The Generalized Gradient Approximation (GGA) and GGA+U schemes have been used as exchange-correlation functional for the above calculations. From the ground state calculation, LaCoTiIn EQHA with a Type-III structure in the ferromagnetic (FM) state is found to be stable. The electronic structure of LaCoTiIn EQHA depicts half-metallic behavior which has metallic overlap in the spin up ([Formula: see text] channel and a semiconductor band gap in the other channel. The spin–orbit coupling of LaCoTiIn has a great influence on the band gap of the material. The computed band gap values for the spin down ([Formula: see text] channel are 0.480 eV and 0.606 eV by using the GGA and GGA+U schemes. The total spin magnetic moment is 1 [Formula: see text], according to the Slater–Pauling rule, [Formula: see text] = ([Formula: see text] - 18) [Formula: see text]. These results obtained can be used as a valuable reference for future research, or they will be used to further motivate the experimental synthesis of the corresponding alloy.

Investigation of Structural, Electronic and Thermoelectric Properties of Two-Dimensional Graphdiyne/Borophene Monolayers and Hetero-bilayers

The integration of dissimilar 2D materials is important for nanoelectronic and thermoelectric applications. Among different polymorphs and different bond geometries, borophene and graphdiyne are two promising candidates for these applications. In the present paper, we have studied hetero-bilayers comprising graphdiyne-borophene (GDY-BS) sheets. Three structural models, namely S0, S1 and S2 have been used for borophene sheets. The optimum interlayer distance for the hetero-bilayers was obtained through binding energy calculations. Then, the structure and electronic properties of the monolayers and hetero-bilayers were individually examined and compared. Graphdiyne monolayer was shown to be a semiconductor with a band gap of 0.43 eV, while the borophene monolayers, as well as all studied hetero-bilayers showed metallic behavior. The thermoelectric properties of borophene and graphdiyne monolayers and the graphdiyne-borophene bilayers were calculated on the basis of the semi-classical Boltzmann theory. The results showed signs of improvement in the conductivity behavior of the hetero-bilayers. Furthermore, considering the increase in Seebeck coefficient and the conductivity for all the structures after calculating figure of merit and power factor, a higher power factor and more energy generation were observed for bilayers. These results show that the GDY-BS hetero-bilayers can positively affect the performance of thermoelectric devices,

First-principles calculations of elastic and optical properties of Aluminum Nitride (AlN) in cubic and hexagonal phase

Investigation of elastic and optical properties of AlN in rock salt, zinc blende, and wurtzite phase is done under the framework of Density Functional Theory (DFT) with modified Becke Johnson Generalised Gradient Approximation (mBJ-GGA) as exchange-correlation functional. Elastic properties conclude the bonding nature of the AlN in the rock salt phase is covalent and stiffest, while the bonding nature in the zinc blende and wurtzite phase is found to be ionic and less stiff. The ratio of bulk modulus to shear modulus indicates AlN is brittle in all three phases. The calculated Debye temperature in all three phases is in good agreement with the available theoretical and experimental works. The optical properties calculation shows the AlN is transparent in the low energy range and it has the metallic behavior in the energy range 7.5eV to 10 eV. At the same time, the compound loses its transparency at the high energy range. Our calculated value of the refractive index of AlN in the rock salt, zinc blende, and wurtzite phases is in good agreement with the available experimental and theoretical works.

Investigation of the Effect of 3d TM-TM Atom Co-Doped in Graphene Nanosheet: DFT Based Calculations

Graphene, an interesting 2D system has a rare electronic structure of two inverted Dirac cones touching at a single point, with great electron mobility and promising microelectronics applications. In the present article, a theoretical investigation has been performed on the structural, electronic, and magnetic properties of pristine graphene nanosheet and also the effect of 3d transition metal (TM) co-doped in graphene nanosheet within the density functional theory framework. 3d TM is categorized into two groups: Cr- group (Cr-Cr, Cr-Mn, and Cr-Fe) and Ni-group (Ni-Cr, Ni-Ti, Ni-Mn). After co-doping TM atoms on graphene, it still holds its planar shape which refers to the stability of these co-doped graphene nanosheets. This is also confirmed by the increasing bond length of carbon and TM atoms on graphene nanosheets. Highest zero-point energies have been found of -12049.24eV and -10936.87eV respectively for Cr-Cr and Ni-Cr co-doped graphene nanosheet. According to Mulliken's charge and electron density differences, all the TM atoms can act as electron donors while the graphene nanosheet is electron acceptor. All the TMs co-doped graphene nanosheet show metallic behavior in terms of band structures and DOS plots except Ti-Ni which has shown a little band gap. In terms of electronic properties, Cr-Cr and Ni-Cr co-doped graphene nanosheets are found most stable among the other studied systems and they can exhibit magnetic behavior as there is a variation in their up and down spin as shown in spin polarized DOS. That’s why they are beneficial to the application of various magnetic devices as well as sectors. Besides Cr-group co-doped graphene nanosheet can exhibit better magnetic properties than Ni-group.

Non-centrosymmetric superconductor Th$$_4$$Be$$_{{33}}$$Pt$$_{{16}}$$ and heavy-fermion U$$_4$$Be$$_{{33}}$$Pt$$_{{16}}$$ cage compounds

Unconventional superconductivity in non-centrosymmetric superconductors has attracted a considerable amount of attention. While several lanthanide-based materials have been reported previously, the number of actinide-based systems remains small. In this work, we present the discovery of a novel cubic complex non-centrosymmetric superconductor $${\text {Th}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ Th 4 Be 33 Pt 16 ($$I{\bar{4}}3d$$ I 4 ¯ 3 d space group). This intermetallic cage compound displays superconductivity below $$T_{\text {c}} = 0.90 \pm 0.04$$ T c = 0.90 ± 0.04 K, as evidenced by specific heat and resistivity data. $${\text {Th}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ Th 4 Be 33 Pt 16 is a type-II superconductor, which has an upper critical field $${\text {H}}_{{\text {c}}2} = 0.27$$ H c 2 = 0.27 T and a moderate Sommerfeld coefficient $$\gamma _{\text {n}} = 16.3 \pm 0.8$$ γ n = 16.3 ± 0.8 mJ $${\text {mol}}^{-1}_{\text {Th}}$$ mol Th - 1 $${\text {K}}^{-2}$$ K - 2 . A non-zero density of states at the Fermi level is evident from metallic behavior in the normal state, as well as from electronic band structure calculations. The isostructural $${\text {U}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ U 4 Be 33 Pt 16 compound is a paramagnet with a moderately enhanced electronic mass, as indicated by the electronic specific heat coefficient $$\gamma _{\text {n}} = 200$$ γ n = 200 mJ $${\text {mol}}^{-1}_{\text {U}}$$ mol U - 1 $${\text {K}}^{-2}$$ K - 2 and Kadowaki–Woods ratio $$A/\gamma ^2 = 1.1 \times 10^{-5}$$ A / γ 2 = 1.1 × 10 - 5 $$\upmu $$ μ $$\Omega $$ Ω cm $${\text {K}}^2$$ K 2 $${\text {mol}}_{\text {U}}^2$$ mol U 2 (mJ)$$^{-2}$$ - 2 . Both $${\text {Th}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ Th 4 Be 33 Pt 16 and $${\text {U}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ U 4 Be 33 Pt 16 are crystallographically complex, each hosting 212 atoms per unit cell.

Electronic properties of SmxSr1−xMnO3 for solid oxide fuel cell application — a first-principles study

Electronic properties of orthorhombic SSM ([Formula: see text] and monoclinic SSM ([Formula: see text] are investigated using the first-principles calculation. The half-metallic behavior that leads to the mixed ionic and electronic conductivity (MIEC) property is identified in orthorhombic SSM. In addition, the strong covalent bonding between [Formula: see text]-p and [Formula: see text]-s orbitals of orthorhombic SSM is identified from the PDOS plot. The strong covalent bonding enhances the [Formula: see text] molecular adsorption on Mn atom. On the other hand, monoclinic SSM shows the pure conducting behavior and there is no covalent bonding between Mn and O atoms. Thus, the results suggest that the half-metal Sm[Formula: see text]Sr[Formula: see text]MnO3 might be a suitable cathode material for intermediate-temperature solid oxide fuel cells.

Tuning the electronic and magnetic properties of defect blue phosphorene by the adsorption of nonmetal atoms

Based on the first principles of density functional theory, the adsorption of nonmetallic atoms on the surface of defective blue phosphorene was investigated. The results show that the most stable sites of different nonmetallic atoms on the defect blue phosphorene are different. The nonmetal (B, C, N, O) atoms were adsorbed on SV and SW defects blue phosphorene respectively. It was observed that B, N adsorbed SV defect blue phosphorene systems exhibited semiconducting behavior, whereas O adsorbed SV defect blue phosphorene system exhibited metallic behavior, and C adsorbed SV defect blue phosphorene system exhibited magnetic semiconducting behavior. For SW defect blue phosphorene, the results show that B, N, adsorbed SW defect blue phosphorene showed magnetic semiconductor behavior, while C, O adsorbed SW defect blue phosphorene showed semiconductor behavior.

Influence of trap densities in ITO thin film on the optical, electrical, and surface plasmon resonance properties

Indium–tin–oxide (ITO) is a material having metallic behavior in the infra-red spectral range. Its electrical and optical properties are also easily tuned, making it a suitable alternative plasmonic material in the infra-red region. In this work, electrical and optical simulation modeling was performed to study the effect of trap densities in different carrier scattering mechanisms on the mobility in ITO. This study correlates the micro-structural and opto-electronic parameters to the surface plasmon resonance (SPR) behavior in the ITO thin films. The results indicate that low defect density with high carrier concentration can provide better SPR performance in ITO.