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EuIr4In2Ge4 is a new intermetallic semiconductor that adopts a non-centrosymmetric structure in the tetragonal ${I\bar 42m}$ space group with unit cell parameters a=6.9016(5) Å and c=8.7153(9) Å. The compound features an indirect optical band gap Eg=0.26(2) eV, and electronic-structure calculations show that the energy gap originates primarily from hybridization of the Ir 5d orbitals, with small contributions from the Ge 4p and In 5p orbitals. The strong spin-orbit coupling arising from the Ir atoms, and the lack of inversion symmetry leads to significant spin splitting, which is described by the Dresselhaus term, at both the conduction- and valence-band edges. The magnetic Eu2+ ions present in the structure, which do not play a role in gap formation, order antiferromagnetically at 2.5 K. [ABSTRACT FROM AUTHOR]

EuIr4In2Ge4 is a new intermetallic semiconductor that adopts a non-centrosymmetric structure in the tetragonal I̅ 42m space group with unit cell parameters a=6.9016(5) Å and c=8.7153(9) Å. The compound features an indirect optical band gap Eg=0.26(2) eV, and electronic-structure calculations show that the energy gap originates primarily from hybridization of the Ir 5d orbitals, with small contributions from the Ge 4p and In 5p orbitals. The strong spin-orbit coupling arising from the Ir atoms, and the lack of inversion symmetry leads to significant spin splitting, which is described by the Dresselhaus term, at both the conduction- and valence-band edges. The magnetic Eu2+ ions present in the structure, which do not play a role in gap formation, order antiferromagnetically at 2.5 K. [ABSTRACT FROM AUTHOR]

In diverse classes of organic optoelectronic devices, controlling charge injection, extraction, and blocking across organic semiconductor-inorganic electrode interfaces is crucial for enhancing quantum efficiency and output voltage. To this end, the strategy of inserting engineered interfacial layers (IFLs) between electrical contacts and organic semiconductors has significantly advanced organic light-emitting diode and organic thin film transistor performance. For organic photovoltaic (OPV) devices, an electronically flexible IFL design strategy to incrementally tune energy level matching between the inorganic electrode system and the organic photoactive components without varying the surface chemistry would permit OPV cells to adapt to ever-changing generations of photoactive materials. Here we report the implementation of chemically/environmentally robust, low-temperature solution-processed amorphous transparent semiconducting oxide alloys, In-Ga-O and Ga-Zn-Sn-O, as IFLs for inverted OPVs. Continuous variation of the IFL compositions tunes the conduction band minima over a broad range, affording optimized OPV power conversion efficiencies for multiple classes of organic active layer materials and establishing clear correlations between IFL/photoactive layer energetics and device performance. [ABSTRACT FROM AUTHOR]

Large plate crystals of LaPtGe2 have been grown by using an inert indium metal flux. This compound crystallizes in the CeNiSi2-type structure (orthorhombic space group Cmcm) with lattice parameters a = 4.3770(9) Å, b = 17.186(3) Å, and c = 4.3942(9) Å. The structure of LaPtGe2 is a three-dimensional framework with alternating PbO-type layers of PtGe and infinite Ge chains, separated by La atoms. Electrical resistivity and Hall effect measurements characterize LaPtGe2 as a metal with holes that act as the charge carriers. Strong temperature dependence of the Hall coefficient and a violation of Kohler's rule (from magnetoresistance data) both indicate possible multiband effects. The electronic structure calculations suggest the metallic nature of LaPtGe2 and show that the strongest bonding exists between Pt and Ge within the PbO-type layers. [ABSTRACT FROM AUTHOR]

The Rashba effect is spin degeneracy lift originated from spin- orbit coupling under inversion symmetry breaking and has been intensively studied for spintronics applications. However, easily implementable methods and corresponding materials for directional controls of Rashba splitting are still lacking. Here, we propose organic-inorganic hybrid metal halide perovskites as 3D Rashba systems driven by bulk ferroelectricity. In these materials, it is shown that the helical direction of the angular momentum texture in the Rashba band can be controlled by external electric fields via ferroelectric switching. Our tight-binding analysis and first-principles calculations indicate that S=1=2 and J =1=2 Rashba bands directly coupled to ferroelectric polarization emerge at the valence and conduction band edges, respectively. The coexistence of two contrasting Rashba bands having different compositions of the spin and orbital angular momentum is a distinctive feature of these materials. With recent experimental evidence for the ferroelectric response, the halide perovskites will be, to our knowledge, the first practical realization of the ferroelectric-coupled Rashba effect, suggesting novel applications to spintronic devices. [ABSTRACT FROM AUTHOR]

The effect of magnesium on grain boundary cohesion in aluminum was investigated by means of first-principles calculations using the Rice-Wang model [Rice and Wang, Mater. Sci. Eng. A 107, 23 (1989)]. It is demonstrated that magnesium is a cohesion enhancer with a potency of -0.11 eV/atom. It is further determined through electronic structure and bonding character analysis that the cohesion enhancing property of magnesium is due to a charge transfer mechanism which is unusually strong and overcomes the negative result of the size effect mechanism. Consistent with experimental results, this work clarifies the controversy and establishes that Mg segregation does not contribute to stress corrosion cracking in Al alloys. [ABSTRACT FROM AUTHOR]

Poly(2,5-bis(3-tetradecylthiophen-2yl)thieno(3,2-b)thiophene) (PBTTT-C14) is an important electro-optical polymer, whose three-dimensional crystal structure is somewhat ambiguous and the fundamental electronic and linear optical properties are not well known. We carried out first-principles calculations to model the crystal structure and to study the effect of side-chains on the physical structure and electronic properties. Our calculations suggest that the patterns of side-chain has little direct effect on the valence band maximum and conduction band minimum but they do have impact on the bandgap through changing the π-π stacking distance. By examining the band structure and wave functions, we conclude that the fundamental bandgap of the PBTTT-C14 crystal is determined by the conduction band energy at the Q point. The calculations indicate that the bandgap of PBTTT-C14 crystal may be tunable by introducing different side-chains. The significant peak in the imaginary part of the dielectric function arises from transitions along the polymer backbone axis, as determined by the critical-point analysis and the large optical transition matrix elements in the direction of the backbone. [ABSTRACT FROM AUTHOR]

Given the recent success in achieving efficient organic photovoltaic solar cells based on thieno[3,4- b]thiophene/benzodithiophene polymers (PTB7) and growing efforts tofurther improve the power conversion efficiency of the PTB7-based devices, a detailed atomic-scale picture of the electronic structure and the excitonic properties of PTB7 crystal is highly desirable. We report electronic and optical properties of PTB7 on the basis of first-principles density functional theory and GW many-body plus Bethe-Salpeter equation (GW-BSE) calculations. It is established that the first two highest valence bands (HVBs) and the first two lowest conduction bands (LCBs) originate from the benzodithiophene and thieno[3,4-b]thiophene functional units, respectively, thus confirming the donor-acceptor nature of PTB7. A significant difference of band splitting between HVBs and LCBs is found and its origins are explained. Our results strongly suggest that the strength of the interchain π -π interaction is not only a function of interchain distance, but is also highly dependent on the nature of the fused rings. The experimental optical absorption spectrum of PTB7 is well reproduced and explained by our GW-BSE calculations. Further analysis shows that the nature of the lowest singlet (triplet) excitons in polymeric crystals such as PTB7 differs from that of organic molecular crystals. A possible reason is explored by combining BSE calculations with a simple Hamiltonian model. [ABSTRACT FROM AUTHOR]

Despite boron being a common alloying element in aluminum, its segregation into the aluminum grain boundary and its effect on the grain boundary strength have not been studied. Here, the electronic structures of the boron-doped Σ5(012)[100] symmetrical tilt grain boundary and (012) free surface systems for aluminum are investigated by means of first-principles calculations using the full-potential linearized augmented plane-wave method with the generalized gradient approximation, within the framework of the Rice-Wang thermodynamic model and the theoretical tensile test approach. We establish that boron has a large driving force to segregate from AI bulk to the symmetrical grain boundary hollow site, and its segregation significantly enhances the grain boundary strength. Through precise calculations on both the grain boundary and free surface environments, it is found that boron is a strong cohesion enhancer in aluminum with a potency of -0.19 eV/atom. An analysis in terms of the relaxed atomic and electronic structures and bonding characters shows that the aluminum-boron bond has mixed covalent and metallic character and is strong in both grain boundary and free surface environments. The strengthening effect of boron is due to creation of additional B-A1 bonds across the grain boundary, which are as strong as existing Al-Al transgranular bonds and thus significantly increase grain boundary adhesion and its resistance to tensile stress and cracking. [ABSTRACT FROM AUTHOR]

Abstract: Aluminum–zinc alloys have an extensive range of structural applications, but their susceptibility to intergranular stress corrosion cracking limits their wider use. In the present work the influence of zinc on a ∑5(012)[100] aluminum grain boundary was investigated by means of first principles calculations with the full potential linearized augmented plane wave method using two approaches: (i) within the framework of the Rice–Wang thermodynamic model; (ii) by the ab initio tensile test method. We determined the most energetically favorable segregation site of Zn along the Al grain boundary, its segregation energy from the Al grain boundary, the possible fracture paths of the grain boundary with Zn and the corresponding fracture energies. We established that Zn has a large driving force (−0.19eVatom−1) for segregation from the Al bulk to the asymmetrical grain boundary site, and its segregation reduces the grain boundary strength slightly. Unusually, segregation of larger atomic size Zn leads to grain boundary contraction. Through precise calculations it was confirmed that zinc is a weak embrittler with a potency of +0.05eVatom−1. Analysis in terms of the relaxed atomic and electronic structures and bonding characters showed that aluminum–zinc bonds have a metallic character in both grain boundary and free surface environments. This work provides a fundamental quantitative understanding of Zn-induced grain boundary embrittlement in Al alloys on the electronic level and establishes that Zn segregation is one of the factors contributing to stress corrosion cracking in Al alloys. [Copyright &y& Elsevier]

We theoretically predict that the series of Pb-based layered chalcogenides, PbnBi2Sen+3 and PbnSb2Ten+3, are possible new candidates for topological insulators, and the topological phases are changed from a topological insulator to a band insulator with increasing n. Among the new topological insulators, we found a large bulk band gap of 0.40 eV in PbBi2Se4, and that of Pb2Sb2Te5 is located near the phase boundary between a trivial and a nontrivial topological insulator, which raises the possibility of tuning the topological phase by changing the external parameters. [ABSTRACT FROM AUTHOR]

Abstract: Based on results of density functional theory (DFT) calculations with the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), we propose a new magnetic material, CsCl-type FeSe. The calculations reveal the existence of ferromagnetic (FM) and antiferromagnetic (AFM) states over a wide range of lattice constants. At 3.12Å in the GGA, the equilibrium state is found to be AFM with a local Fe magnetic moment of . A metastable FM state with Fe and Se local magnetic moments of 2.00 and , respectively, lies 171.7meV above the AFM state. Its equilibrium lattice constant is smaller than that of the AFM state, implying that when the system undergoes a phase transition from the AFM state to the FM one, the transition is accompanied by volume contraction. Such an AFM–FM transition is attributed to spin-density z-reflection symmetry; the symmetry driven AFM–FM transition is not altered by spin–orbit coupling. The relative stability of different magnetic phases is discussed in terms of the local density of states. We find that CsCl-type FeSe is mechanically stable, but the magnetic states are expected to be brittle. [Copyright &y& Elsevier]

EuIr4In2Ge4 is a new intermetallic semiconductor that adopts a non-centrosymmetric structure in the tetragonal ${I\bar 42m}$ space group with unit cell parameters a=6.9016(5) Å and c=8.7153(9) Å. The compound features an indirect optical band gap Eg=0.26(2) eV, and electronic-structure calculations show that the energy gap originates primarily from hybridization of the Ir 5d orbitals, with small contributions from the Ge 4p and In 5p orbitals. The strong spin-orbit coupling arising from the Ir atoms, and the lack of inversion symmetry leads to significant spin splitting, which is described by the Dresselhaus term, at both the conduction- and valence-band edges. The magnetic Eu2+ ions present in the structure, which do not play a role in gap formation, order antiferromagnetically at 2.5 K. [ABSTRACT FROM AUTHOR]

EuIr4In2Ge4 is a new intermetallic semiconductor that adopts a non-centrosymmetric structure in the tetragonal I̅ 42m space group with unit cell parameters a=6.9016(5) Å and c=8.7153(9) Å. The compound features an indirect optical band gap Eg=0.26(2) eV, and electronic-structure calculations show that the energy gap originates primarily from hybridization of the Ir 5d orbitals, with small contributions from the Ge 4p and In 5p orbitals. The strong spin-orbit coupling arising from the Ir atoms, and the lack of inversion symmetry leads to significant spin splitting, which is described by the Dresselhaus term, at both the conduction- and valence-band edges. The magnetic Eu2+ ions present in the structure, which do not play a role in gap formation, order antiferromagnetically at 2.5 K. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) electronic systems are of wide interest due to their richness in chemical and physical phenomena and potential for technological applications. Here we report that [Pb2BiS3][AuTe2], known as the naturally occurring mineral buckhornite, hosts 2D carriers in single-atomthick layers. The structure is composed of stacking layers of weakly coupled [Pb2BiS3] and [AuTe2] sheets. The insulating [Pb2BiS3] sheet inhibits interlayer charge hopping and confines the carriers in the basal plane of the single-atom-thick [AuTe2] layer. Magneto-transport measurements on synthesized samples and theoretical calculations show that [Pb2BiS3][AuTe2] is a multiband semimetal with a compensated density of electrons and holes, which exhibits a high hole carrier mobility of ∼1360 cm2/(V s). This material possesses an extremely large anisotropy, Γ = ρc/ρab ≈ 104 comparable to those of the benchmark 2D materials graphite and Bi2Sr2CaCu2O6+δ. The electronic structure features linear band dispersion at the Fermi level and ultrahigh Fermi velocities of 106 m/s, which are virtually identical to those of graphene. The weak interlayer coupling gives rise to the highly cleavable property of the single crystal specimens. Our results provide a novel candidate for a monolayer platform to investigate emerging electronic properties. [ABSTRACT FROM AUTHOR]

Two new compounds CsCdInQ3(Q = Se, Te) have been synthesizedusing a polychalcogenide flux. CsCdInQ3(Q = Se, Te) crystalsare promising candidates for X-ray and γ-ray detection. Thecompounds crystallize in the monoclinic C2/cspace group with a layered structure, which is relatedto the CsInQ2(Q = Se, Te) ternary compounds. The cellparameters are: a= 11.708(2) Å, b= 11.712(2) Å, c= 23.051(5) Å, β= 97.28(3)° for CsCdInSe3and a=12.523(3) Å, b= 12.517(3) Å, c= 24.441(5) Å, β = 97.38(3)° for CsCdInTe3. Both the Se and Te analogues are wide-band-gap semiconductors withoptical band gaps of 2.4 and 1.78 eV for CsCdInSe3andCsCdInTe3, respectively. High-purity polycrystalline rawmaterial for crystal growth was synthesized by the vapor transfermethod for CsCdInQ3. Large single crystals up to 1 cm havebeen grown using the vertical Bridgman method and exhibit photoconductiveresponse. The electrical resistivity of the crystals is highly anisotropic.The electronic structure calculation within the density functionaltheory (DFT) framework indicates a small effective mass for the carriers.Photoconductivity measurements on the as grown CsCdInQ3crystals gives high carrier mobility-lifetime (μτ) productscomparable to otherdetector materials such as α-HgI2, PbI2, and CdxZn1–xTe (CZT). [ABSTRACT FROM AUTHOR]

Linear optical properties of regio-regular-poly(3-hexythiophene) (rr-P3HT) and regio-regular-poly(3-hexyselenophene) (rr-P3HS) are investigated in relation to their anisotropic crystal structure by means of first-principles density functional calculations. The optical spectra are evaluated by calculating its dielectric functions, focusing on the frequency dependence of the imaginary part. The optical transition along the π conjugation-connecting backbone direction is found to be the most significant at the band edges. A group-theoretical analysis of the matrix elements is given to explain the interband transitions. The optical spectra, electronic structures, and structural stabilities are calculated using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the local-density approximation. We proposed several possible crystal structures of rr-P3HT and performed structural optimizations to determine a stable structure. Comparing the total energy differences among these relaxed structures, a base-centered monoclinic structure belonging to the space group A2 is found to be the most stable structure. In the electronic structure, C and S orbitals belonging to polythiophene backbones are the biggest contributors at the valence band maximum and conduction band minimum, but there is almost no contribution from the hexyl side chains. Last, the differences in electronic and optical properties between rr-P3HT and rr-P3HS are discussed. [ABSTRACT FROM AUTHOR]

In order to address the growing need for p-type transparent conducting oxides (TCOs), we present a materials design approach that allows to search for materials with desired properties. We put forward a set of design principles (DPs) that a material must meet in order to qualify as a p-type TCO. We then start from two prototype p-type binary oxides, i.e., Cu2O and Ag2O, and define a large group of compounds in which to search for unique candidate materials. From this set of compounds, we extracted two oxovanadates, Cu3VO4 and Ag3VO4, which serve as a case study to show the application of the proposed materials selection procedure driven by the DPs. Polycrystalline Ag3VO4 was synthesized by a water-based hydrothermal technique, whereas Cu3VO4 was prepared by a solid-state reaction. The theoretical study of the thermochemistry, based on first-principles electronic structure methods, demonstrates that Cu3VO4 and α-Ag3VO4 are p-type materials that show intrinsic hole-producing defects along with a low concentration of "hole-killing" defects. Owing to its near-perfect stoichiometry, Ag3VO4 has a rather low hole concentration, which coincides with the experimentally determined conductivity limit of 0.002 S/cm. In contrast, Cu3VO4 is highly off stoichiometric, Cu3-xVO4 (x = 0.15), which raises the amount of holes, but due to its black color, it does not fulfill the requirements for a p-type TCO. The onset of optical absorption in α-Ag3VO4 is calculated to be 2.6 eV, compared to the experimentally determined value of 2.1 eV, which brings it to the verge of transparency. [ABSTRACT FROM AUTHOR]

We report the synthesis, structure, spectroscopic properties, charge and thermal transport, and electronic structure of a new member of the Zintl family, Yb[sub5]AI[sub2]Sb[sub6]. The compound crystallizes in the Ba[sub5]AI[sub2]Bi[sub6] structure type and requires the addition of Ge or Si in the synthesis, which appears to act as a catalyst. Yb[sub5]AI[sub2]Sb[sub6] has an anisotropic structure with infinite anionic double chains cross-linked by Yb[sup2+] ions. Polycrystalline ingots of Yb[sub5]AI[sub2]Sb[sub6] prepared in the presence of 0.5 mol equiv of Ge showed room-temperature conductivity, thermopower, and thermal.conductivity of ∼1100 S/cm, ∼20 μV/K, and ∼3.8 W/m∙K, respectively. Investigations of other solid solutions of Yb[sub5]AI[sub2]Sb[sub6], doping effects, and chemical modifications are discussed. Sr only partially replaces Yb in the structure leading to Sr[sub0.85]Yb[sub4.15]Al[sub2]Sb[sub6]. Eleptronic structure calculations performed using a highly precise full-potential linearized augmented plane wave method within the density functional theory scheme show the presence of a negative band gap and suggest incomplete electron transfer and a metallic character to the compound. [ABSTRACT FROM AUTHOR]

The Cs5BiP4Se12 salt grows naturally as nanowires that crystallize in the polar space group Pmc21, with a = 7.5357(2) Å, b = 13.7783(6) Å, C = 28.0807(8) Å, and Z = 4 at 293(2) K. The compound features octahedral [Bi(P2Se6)2]5 coordination complexes that stack via weak intermolecular SeߪSe interactions to form long, flexible fibers and nanowires. The Cs5BiP4Se12 fibers are transparent in the near- and mid-IR ranges and were found to exhibit a nonlinear optical second harmonic generation response at 1 μm that is approximately twice that of the benchmark material AgGaSe2. The material has a nearly direct band gap of 1.85 eV and melts congruently at 590 °C. Ab initio electronic structure calculations performed with the full-potential linearized augmented plane wave (FLAPW) method show that the band gap increases from its local density approximation (LDA) spin-orbit coupling value of 1.15 eV to the higher value of 2.0 eV when the screened-exchange LDA method is invoked and explain how the long nanowire nature of Cs5BiP4Se12 emerges. [ABSTRACT FROM AUTHOR]