We report on detailed structural, electronic and magnetic studies of GdMn$_{1-x}$Cr$_x$O$_3$ for Cr doping levels 0 $\le$ $x$ $\le$ 1. In the solid solutions, the Jahn-Teller distortion associated with Mn$^{3+}$ ions gives rise to major changes in the ${bc}$-plane sub-lattice and also the effective orbital ordering in the ${ab}$-plane, which persist up to the compositions $x$ $\sim$ 0.35. These distinct features in the lattice and orbital degrees of freedom are also correlated with $bc$-plane anisotropy of the local Gd environment. A gradual evolution of electronic states with doping is also clearly seen in O $K$-edge x-ray absorption spectra. Evidence of magnetization reversal in field-cooled-cooling mode for $x$ $\ge$ 0.35 coinciding the Jahn-Teller crossover, suggests a close correlation between magnetic interaction and structural distortion. These observations indicate a strong entanglement between lattice, spin, electronic and orbital degrees of freedom. The nonmonotonic variation of remnant magnetization can be explained by doping induced modification of magnetic interactions. Density functional theory calculations are consistent with a layer-by-layer type doping with ferromagnetic (antiferomagnetic) coupling between Mn (Cr) ions for intermediate compound ($x$ = 0.5), which is distinct from that observed for the end members GMnO$_3$ and GdCrO$_3$.
Thermodynamics and kinetics of Li, Na, and Mg storage in Ge is studied ab initio. The most stable configurations can consist of tetrahedral, substitutional, or a combination of the two types of sites. In the dilute limit, Li, Na prefer interstitial, while Mg prefers substitutional sites. At higher concentrations of Li, Na, and Mg, there is a combination of interstitial and substitutional sites. This is an important finding, as previous ab initio studies of alloying type electrode materials ignored substitutional sites. Insertion energies computed at dilute concentration (x = 1/64) show that Na…
Solar thermochemical hydrogen production (STCH) is a renewable alternative to hydrogen produced using fossil fuels. While serial bulk experimental methods can accurately measure STCH performance, screening chemically complex materials systems for new promising candidates is more challenging. Here we identify double-site Ce-substituted (Ba,Sr)MnO3 oxide perovskites as promising STCH candidates using a combination of bulk synthesis and high-throughput thin film experiments. The Ce substitution on the B-site in 10H-BaMnO3 and on the A-site in 4P-SrMnO3 lead to 2-3x higher hydrogen production comp…
Ca$_3$Ti$_2$O$_7$ is an experimentally confirmed hybrid improper ferroelectric material, in which the electric polarization is induced by a combination of the coherent TiO$_6$ octahedral rotation and tilting. In this work, we investigate the tuning of ferroelectricity of Ca$_3$Ti$_2$O$_7$ using iso-valent substitutions on Ca-sites. Due to the size mismatch, larger/smaller alkaline earths prefer $A$'/$A$ sites respectively, allowing the possibility for site-selective substitutions. Without extra carriers, such site-selected iso-valent substitutions can significantly tune the TiO$_6$ octahedral …
Heusler alloy Fe2CrAl exhibits a ferromagnetic behaviour below Curie temperature (TC) ~ 202 K along with presence of cluster glass (CG) phase near freezing temperature (Tf) ~ 3.9 K and Griffiths phase (GP) above 300 K. The physical properties of this alloy are very sensitive to substitutions and anti-site disorder. Here, we investigate the effect of partial substitution of Mo at Cr-site on physical properties of Fe2CrAl. Structural and morphological analysis confirms the single cubic structure of the substituted alloys. Increment in Mo concentration shifts the TC towards lower temperature, whi…
By understanding the small easy axis magnetocrystalline anisotropy energy (MAE) of hexagonal Ce2Co17, an attempt has been made to improve anisotropy and consequently to obtain better characteristics for a high energy permanent magnet via site selective substitutional doping of Ce/Co with suitable elements. The present calculations of the electronic and magnetic properties of Ce2Co17 and related substituted compounds have been performed using the full potential linear augmented plane wave (FPLAPW) method within the generalized gradient approximation (GGA). Sm-substituted compounds were simulate…
We theoretically study the structural stability of $R$Fe$_{12}$ with the ThMn$_{12}$ structure ($R$: rare-earth elements, La, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, Lu, Y, or Sc, or group-IV elements, Zr or Hf) based on density functional theory. The formation energy has a strong correlation with the atomic radius of $R$. The formation energy relative to simple substances decreases as the atomic radius decreases, except for $R=$ Sc and Hf, while that relative to $R_{2}$Fe$_{17}$ and bcc Fe has a minimum for $R=$ Dy. The present results are consistent with recent experimental reports in which the part…
We report magnetocrystalline anisotropy of pure and Fe/Si substituted SmCo5. The calculations were performed using the advanced density functional theory (DFT) including onsite electron-electron correlation and spin orbit coupling. Si substitution substantially reduces both uniaxial magnetic anisotropy and magnetic moment. Fe substitution with the selective site, on the other hand, enhances the magnetic moment with limited chemical stability. The magnetic hardness of SmCo5 is governed by Sm 4f localized orbital contributions, which get flatten and split with the substitution of Co (2c) with Si…
Extended defects such as stacking faults and anti-site domain boundaries can perturb the band edges in Cu$_2$ZnSnS$_4$ and Cu$_2$ZnSnSe$_4$, acting as a weak electron barrier or a source for electron capture, respectively. In order to find ways to prohibit the formation of planar defects, we investigated the effect of chemical substitution on the stability of the intrinsic stacking fault and metastable polytypes and analyze their electrical properties. Substitution of Ag for Cu makes stacking faults less stable, whereas the other substitutions (Cd and Ge) promote their formation. Ge substituti…
Structural Stability, Electronic, Magnetic and Optical Properties of Rectangular Graphene and Boron-Nitride Quantum Dots: Effects of Size, Substitution and Electric Field
Based on genetic evolution algorithm, universal structure predictor USPEX assists to explore the most stable structure from Na+ substituting Ca2+ under variable concentration, for p type transparent conductive oxide application. The study finds 2 atoms of NaCa maintain the octahedral packing and cubic phase without the presence of oxygen vacancy, but the electron loss causes in fermi level entering into valence band, realizing p type TCOs character. While others still remain insulator character due to the compensation of oxygen vacancy. Applying Al3+ substituting Ca2+ achieve the fermi level i…
Giant magnetocaloric (GMC) materials constitute a requirement for near room temperature magnetic refrigeration. (Fe,Mn)$_2$(P,Si) is a GMC compound with strong magnetoelastic coupling. The main hindrance towards application of this material is a comparably large temperature hysteresis, which can be reduced by metal site substitution with a nonmagnetic element. However, the (Fe,Mn)$_2$(P,Si) compound has two equally populated metal sites, the tetrahedrally coordinated $3f$ and the pyramidally coordinated $3g$ sites. The magnetic and magnetocaloric properties of such compounds are highly sensiti…
We investigate the effects of Fe and Co substitutions on the phase stability of the martensitic phase, mechanical, electronic and magnetic properties of magnetic shape memory system Mn$_{2}$NiGa by first-principles Density functional theory(DFT) calculations. The evolution of these aspects upon substitution of Fe and Co at different crystallographic sites are investigated by computing the electronic structure, mechanical properties and magnetic exchange parameters. We find that the martensitic phase of Mn$_{2}$NiGa gradually de-stabilises with increase in concentration of Fe/Co due to the weak…
The mechanisms underlying the enhancement of magnetic anisotropies (MAs) of Sm ions, owing to valence electrons at the Sm site and the screened nuclear charges of ligands, are clarified using a detailed analysis of crystal fields (CF). In order to investigate the finite-temperature magnetic properties, we developed an effective spin model for SmFe$_{12}X$ ($X$=H, B, C, and N) and SmFe$_{11}M$ ($M$=Ti, V, and Co), where the magnetic moments, CF parameters, and exchange fields were determined by first-principle calculations. Using this model, the MA constants and magnetization curves at finite t…
The high solubility of oxygen in Ti, Zr and Hf makes it difficult to stabilize the protective oxide scales on their surfaces as the subsurface regions can serve as boundless sinks that continuously dissolve oxygen. Alloying elements are crucial to reduce the oxygen solubility and diffusivity within early transition metals. Past studies have shown that substitutional alloying additions to titanium repel interstitial oxygen. Here we use first-principles calculations to show that this repulsion is short ranged and identify a variety of factors that are likely responsible for the repulsive interac…
The electronic structures of TixZrx/2CoPbxTex, TixZrx/2Hfx/2CoPbxTex (x = 0.5), and the parent compound TiCoSb were investigated using the full potential linearized augmented plane wave method. The thermoelectric transport properties of these alloys are calculated on the basis of semi-classical Boltzmann transport theory. From the band structure calculations we show that the substitution of Zr,Hf in the Ti site and Pb and Te in the Sb site lower the band gap value and also change the indirect band (IB) gap of TiCoSb to the direct band (DB) gap. The calculated band gap of TiCoSb, TixZrx/2CoPbxT…
Modulating electronic structure of monolayer transition metal dichalcogenides (TMDCs) is important for many applications and doping is an effective way towards this goal, yet is challenging to control. Here we report the in-situ substitutional doping of niobium (Nb) into TMDCs with tunable concentrations during chemical vapour deposition. Taking monolayer WS2 as an example, doping Nb into its lattice leads to bandgap changes in the range 1.98 eV to 1.65 eV. Noteworthy, electrical transport measurements and density functional theory calculations show that the 4d electron orbitals of the Nb dopa…
Oxide thermoelectrics are exciting due to their chemical and thermal stability at high temperatures. However, the efficacy of these materials are limited by poor figure of merit (zT). In this study, the role of Sr and Mn co-substitution on the thermoelectric properties of NdCoO3 (Nd_{1-x}Sr_xCo_{1-y}Mn_yO_3; 0.00 \leq x \leq 0.10; 0.00 \leq y \leq 0.10) is investigated. The Seebeck coefficient decreases with single Sr substitution at Nd site; however, the Sr and Mn co-substitution enhances the Seebeck coefficient compared to single Sr substitution and is attributed to the localization effect. …
We present a density-functional theory (DFT) study of the structural, electronic, and chemical bonding behaviour in germanium (Ge)-doped vanadium dioxide (VO$_2$). Our motivation is to explain the reported increase of the metal-insulator transition temperature under Ge doping and to understand how much of the fundamental physics and chemistry behind it can be captured at the conventional DFT level. We model doping using a supercell approach, with various concentrations and different spatial distributions of Ge atoms in VO$_2$. Our results suggest that the addition of Ge atoms strongly perturbs…
To understand the effect of isoelectronic substitution on thermoelectric properties of TiCoSb based half - Heusler (HH) alloys, we have systematically studied the transport properties with substitution of Zr at Ti and Bi at Sb sites. The electronic structure of TixZr1-xCoSbxBi1-x (x = 0.25, 0.5, 0.75) and parent TiCoSb are investigated using the full potential linearized augmented plane wave method and the thermoelectric transport properties are calculated on the basis of semiclassical Boltzmann transport theory. The band analysis of the calculated band structures reveal that TixZr1-xCoSbxBi1-…
Mechanical control of electronic and magnetic properties of 2D Van-der-Waals heterostructures gives new possibilities for further development of spintronics and information-related technologies. Using the density functional theory, we investigate the structural, electronic, and magnetic properties of silicene monolayer with substituted Chromium atoms and under a small biaxial strain ($-6\%< ε< 8\%$). Our results indicate that the Cr-doped silicene nanosheets without strain have magnetic metallic, half-metallic or semiconducting properties depending on the type of substitution. We also show tha…
The existence of non-substitutional $β$-Sn defects in Ge$_{1-x}$Sn$_{x}$ was confirmed by emission channeling experiments [Decoster et al., Phys. Rev. B 81, 155204 (2010)], which established that although most Sn enters substitutionally ($α$-Sn) in the Ge lattice, a second significant fraction corresponds to the Sn-vacancy defect complex in the split-vacancy configuration ( $β$-Sn ), in agreement with our previous theoretical study [Ventura et al., Phys. Rev. B 79, 155202 (2009)]. Here, we present our electronic structure calculation for Ge$_{1-x}$Sn$_{x}$, including substitutional $α$-Sn as w…
Molecular dynamics calculations are carried out on pure, Al-substituted, and In-substituted LLZO. The calculations show that the tendency of Al to occupy the 24d sites in LLZO lithium ion conductors is hypothesized here to negatively impact ionic conductivity. The room-temperature ionic conductivity of In-LLZO, in which the In resides at the 48g sites, is predicted to be an order of magnitude higher than Al-LLZO. Consideration of the simple tetrahedral topology of the lithium ion conduction network suggests that the increased conductivity arises because the 48g site sits at a bridge in the lit…
Effects of Fe substitution on the electronic, transport, and magnetic properties of ZnGa$_2$O$_4$: A systematic ab-initio study
采用密度泛函方法研究了Fe掺杂到宽禁带尖晶石ZnGa $_2$ O $_4$的四面体和八面体阳离子位的结构.我们计算了不同的取代的电子结构，并讨论了考虑不同近似的交换相关势的每种情况下的磁性和输运性质。我们表明，对于某些掺杂的情况下，获得的预测行为的显着差异取决于所采用的交换相关电位。概述了掺杂系统作为磁性半导体的可能应用。
We study the electronic and structural properties of substitutional impurities of graphenelike nanoporous materials C$_2$N, $tg$-, and $hg$-C$_3$N$_4$ by means of density functional theory calculations. We consider four types of impurities; boron substitution on carbon sites (B(C)), carbon substitution on nitrogen sites (C(N)), nitrogen substitution on carbon sites (N(C)), and sulfur substitution on nitrogen sites (S(N)). From cohesive energy calculations, we find that the C(N) and B(C) substitutions are the most energetically favorable and induce small bond modifications in the vicinity of th…
Iron and cobalt distannides \ce{MSn2} (M = Fe, Co) are regarded as a promising conversion-type anode material for lithium- and sodium-ion batteries, but their properties are not well understood. In this work, we report a first-principles study of alkali metal (A = Li, Na) substitutional effect on the structural, mechanical, lattice vibrational, electronic and defect properties of these distannides. Special attention is paid to systematic comparison between \ce{FeSn2} and \ce{CoSn2}. Our calculations reveal that M/A substitution induces a lattice expansion and decrease of elastic constants, whi…
Na-site substitution effects of the thermoelectric properties of NaCo_2O_4
测量并分析了Na $_{1+x}$ Co $_2$ O $_4$和Na $_{1.1-x}$ Ca $_x$ Co $_2$ O $_4$的电阻率和热电势。在Na $_{1+x}$ Co $_2$ O $_4$中，电阻率随$x$增加，而热电势几乎与$x$无关。这表明过量的Na不太可能提供载流子，并且减少了样品中的有效导电路径。在Na $_{1.1-x}$ Ca $_x$ Co $_2$ O $_4$中，电阻率和热电势随着$x$而增加，并且Ca $^{2+}$取代Na $^+$减少了NaCo $_2$ O $_4$中的多数载流子。这意味着它们是孔，这与热电势的正号一致。该化合物的电阻率随温度变化的特性证明了该化合物具有很强的相关性。
Dopability in semiconductors plays a crucial role in device performance. Using the first-principles density-functional theory calculations, we investigate systematically the doping properties of layered MX2 (M= Mo, W; X=S, Te) by replacing M or X with the groups III, V and VII elements. It is found that the defect BM is hard to form in MX2 due to the large formation energy originating from the crystal distortion, while AlM is easy to realize compared to the former. In MoS2, WS2 and MoTe2, Al is the most desirable p-type dopant under anion-rich conditions among the group III components, since A…
Cubic spinel CoCr2O4 has attained recent attention due to its multiferroic properties. However, the Co site substitution effect on the structural and magnetic properties has rarely been studied in thin film form. In this work, the structural and magnetic properties of Co1-xNixCr2O4 (x = 0, 0.5) epitaxial thin films deposited on MgAl2O4 (100) and MgO (100) substrates to manipulate the nature of strain in the films using pulsed laser deposition (PLD) technique are presented. The epitaxial nature of the films was confirmed through X-ray diffraction (XRD) and Rutherford backscattering spectrometry…
Zincblende copper iodide has been attracting growing interest as p-type semiconductor for applications in transparent electronics and transparent thermoelectrics. A key step towards technological applications is the possibility to enhance copper iodide (CuI) conductivity by doping without deteriorating transparency. A recent high-throughput computational study revealed that chalcogen substitutions on iodine sites can act as shallow acceptors. Following computational predictions, doping by oxygen, sulfur and selenium substitutions on iodine sites has recently been realized in the laboratory, sh…
Elemental substitution is a proven method of Fermi level tuning in topological insulators, which is needed for device applications. Through static and time resolved photoemission, we show that in MnBi$_2$Te$_4$, elemental substitution of Bi with Sb indeed tunes the Fermi level towards the bulk band gap, making the material charge neutral at 35\% Sb concentration. For the first time, we are able to directly probe the excited state band structure at this doping level, and their dynamics, which show that the decay channels at the Fermi level are severely restricted. However, elemental substitutio…
A first-principles investigation of the electronic and quantum transport properties of double-walled carbon nanotubes doped with nitrogen and boron atoms is presented. Concentric nanotube sidewalls separated by the typical graphitic van der Waals bond distance are found to strongly interact upon incorporation of doping atoms in the hexagonal networks. The local perturbation caused by the doping atoms extends over both shells due to a hybridization of their electronic states, yielding a reduction of the backscattering efficiency as compared with two independent single-walled nanotubes. A multi-…
Tuning magnetic frustration on the diamond lattice of the A-site magnetic spinels CoAl$_{2-x}$Ga$_x$O$_4$: Lattice expansion and site disorder
在金刚石晶格A位上具有磁性Co $^{2+}$离子的尖晶石CoB $_2$ O $_4$可能由于竞争的近邻（$J_1$）和次近邻（$J_2$）相互作用而受到阻碍。在这里，我们描述了尝试调整这些相互作用的相对强度的非磁性B-网站上的取代。我们采用的系统是CoAl $_{2-x}$ Ga $_x$ O $_4$，其中Al被较大的Ga系统地取代，表面上在B位点上。正如预期的那样，Ga取代使晶格膨胀，导致A位上的Co原子彼此被推得更远，从而削弱了磁相互作用。此外，Ga以浓度依赖性方式分布在B和A位点之间，随着$x$的增加，从A位点置换越来越多的Co。这种增加的反转，这是在室温下进行的中子衍射研究证实，影响磁有序非常显着，并改变了基态的性质。磁耦合的建模说明了由阳离子位点无序引起的复杂性。
