Using first-principles calculations, we investigated the magnetic, electronic, and structural properties of oxygen-substituted NaMnF3 (NaMnF1.5O1.5) with in-plane biaxial strain. For simplicity, a structure containing an oxygen octahedron is used to explore the underlying physical mechanism. We found that the oxygen octahedron induces a transition from an insulating antiferromagnet to a high-temperature half-metallic ferromagnet. More importantly, the Curie temperature can be significantly enhanced and even might reach room temperature by applying tensile strain. The changing trends of exchange coupling constants with the increasing biaxial tensile strain can be attributed to the cooperative effects of Jahn-Teller distortion and rotation distortion. It is expected that these findings can enrich the versatility of NaMnF3 and make it a promising candidate for spintronic applications.
The conductive characteristics of Bi0.9La0.1Fe0.96Mg0.04O3(BLFM) thin film are investigated at various temperatures and a negative differential resistance (NDR) is observed in the thin film, where a leakage current peak occurs upon application of a downward electric field above 80 oC. The origin of the NDR behavior is shown to be related to the ionic defect of oxygen vacancies (VO..) present in the film. On the basis of analyzing the leakage mechanism and surface potential behavior, the NDR behavior can be understood by considering the competition between the polarized distribution and neutral…
The series of Mnx(Y0.148Zr0.852)1-xO2-δ ceramics was systematically studied by means of X-ray absorption and emission spectroscopy and DC magnetic susceptibility. XAS and XES results show changes in manganese oxidation state and a gradual evolution of the local atomic environment around Mn ions upon increasing dopants content, which is due to structural relaxation caused by growing amount of oxygen vacancies. Magnetic susceptibility measurements reveal that Mn3O4 precipitates are formed for x greater than or equal to 0.1 and enable independent determination of actual quantity of Mn ions dissol…
We investigated the preferred electron dopants at the oxygen sites of 1111-type SmFeAsO by changing the atmospheres around the precursor with the composition of Sm:Fe:As:O = 1:1:1:1-x in high-pressure synthesis. Under H2O and H2 atmospheres, hydrogens derived from H2O or H2 molecules were introduced into the oxygen sites as a hydride ion, and SmFeAsO1-xHx was obtained. However, when the H2O and H2 sources were removed from the synthetic process, nearly stoichiometric SmFeAsO was obtained and the maximum amount of oxygen vacancies introduced remained x = 0.05(4). Density functional theory calcu…
We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO$_{2\pm x}$ grown by reactive molecular beam epitaxy (MBE). The oxidation conditions induce a switching between ($\bar{1}11$) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and $p$-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxyg…
The magnetic and magnetotransport properties of the oxygen deficient perovskites, SrCo1-xMxO3-d with M = Nb and Ru, were investigated. Both Nb- and Ru-substituted cobaltites are weak ferromagnets, with transition temperatures Tm of 130-150 K and 130-180 K, respectively, and both exhibit a spin glass behavior at temperatures below Tf = 80-90 K. It is demonstrated that there exists a strong competition between ferromagnetism and spin glass state, where Co4+ induces ferromagnetism, whereas Nb or Ru substitution at the cobalt sites induces magnetic disorder, and this particular magnetic behavior i…
Room temperature ferromagnetism was characterized for thin films of SrTi$_{0.6}$Fe$_{0.4}$O$_{3-δ}$ grown by pulsed laser deposition on SrTiO$_{3}$ and Si substrates under different oxygen pressures and after annealing under oxygen and vacuum conditions. X-ray magnetic circular dichroism demonstrated that the magnetization originated from Fe$^{2+}$ cations, whereas Fe$^{3+}$ and Ti$^{4+}$ did not contribute. Films with the highest magnetic moment (0.8 μB per Fe) had the highest measured Fe$^{2+}$:Fe${^3+}$ ratio of 0.1 corresponding to the largest concentration of oxygen vacancies (δ = 0.19). …
The high cost of platinum-based catalysts has hampered the commercialization of polymer electrolyte membrane fuel cells (PEMFCs). Hence, the electronic structure and oxygen reduction ability of [Ti(IV)Pc]2+, Ti(II)Pc titanyl-phthalocyanines, and their tailored peripheral and axial ligand complexes were theoretically investigated to determine non-precious cathode catalysts. Our results revealed that the peripherally substituted and unsubstituted Ti(II)Pc triplet complexes can spontaneously reduce peroxide. The singlet [Ti(IV)Pc]2+ parent complex has a 6.45 eV barrier. However, fluorine substitu…
The double perovskite La2NiMnO6 (LNMO) exhibits complex magnetism due to the competition of magnetic interactions that are strongly affected by structural and magnetic inhomogeneities. In this work, we study the effect of oxygen annealing on the structure and magnetism of epitaxial thin films grown by pulsed laser deposition. The key observations are that a longer annealing time leads to a reduction of saturation magnetization and an enhancement in the ferromagnetic transition temperature. We explain these results based upon epitaxial strain and oxygen defect engineering. The oxygen enrichment…
We use density functional theory (DFT) calculations to show that oxygen vacancies ($v_\mathrm{O}$) and mobility induce noncentrosymmetric polar structures in SrTi$_{1-x-y}$Fe$_{x}$Co$_{y}$O$_{3-δ}$ ($x=y=0.125$) with $δ= \{0.125, 0.25\}$, enhance the saturation magnetization and give rise to large changes in the electric polarization $\vertΔP\vert$. We present an intuitive set of rules for SrTiFeCoO$_{3-δ}$ (STFC), which are based on the interplay between (Co/Fe)-$v_\mathrm{O}$ defects, magnetic cations coordination and topological vacancy disorder. STFC structures convey layered crystals with…
We have investigated the room temperature ferromagnetic order that develops in Al-substituted magnesium oxide, Mg(Al)O, nanoparticles with Al fractions of up to 5 at.%. All samples, including undoped MgO nanoparticles, exhibit room temperature ferromagnetism, with the saturation magnetization reaching a maximum of 0.023 emu/g at 2 at.% of Al. X-ray photoelectron spectroscopy identifies the presence of oxygen vacancies in both doped and undoped MgO nanoparticles, with the vacancy concentration increasing upon vacuum annealing of Mg(Al)O, resulting in two-fold enhancement of the saturation magne…
Plasma engineered Hydroxyl Defects in NiO a DFTSupported-Spectroscopic Analysis of Oxygen Hole States and Implications for Water Oxidation
Technical University of Darmstadt（达姆施塔特工业大学）；Dutch Institute for Fundamental Energy Research（荷兰基础能源研究所）；Università degli studi di Milano（米兰大学）；Max Planck Institute for Chemical Energy Conversion（马克斯·普朗克化学能转换研究所）；Diamond Light Source（钻石光源）
The importance of a high shear coefficient d15 (or d24) to the piezoelectric properties of domain-engineered and polycrystalline ferroelectrics is discussed. The extent of polarization rotation, as a mechanism of piezoelectric response, is directly correlated to the shear coefficient. The terms "rotator" and "extender" are introduced to distinguish the contrasting behaviors of crystals such as 4mm BaTiO3 and PbTiO3. In "rotator" ferroelectrics, where d15 is high relative to the longitudinal coefficient d33, polarization rotation is the dominant mechanism of piezoelectric response; the maximum …
The oxidation of α-Ti(0001) surface was studied using density functional theory. In order to enhance the oxidation resistance, we substituted Ti atoms with Si atoms in Ti(0001) surface. We observe that Si prefers to segregate at the surface layer of Ti(0001) compared to other sub-surface layers. The Si solubility on the Ti(0001) surface was estimated to be around 75 at.%. While Si segregation was found to reduce the binding between the oxygen atom and the Ti(0001) surface, the barrier for oxygen to diffuse into the slab increases. The dissociation of the oxygen molecule on the clean and Si seg…
Electronic Structure and Band-Edge Character of Ga-Substituted $α$-Al$_2$O$_3$: A First-Principles Study
Ivane Javakhishvili Tbilisi State University（伊万·贾瓦希什维利第比利斯国立大学）；New York City College of Technology, The City University of New York（纽约市立学院，纽约市立大学）；The Graduate School and University Center, The City University of New York（研究生院与大学中心，纽约市立大学）；Long Island University（长岛大学）
We have investigated the in-plane thermal conductivity $κ_{ab}(T,H)$ of large single crystals of optimally oxygen-doped (Y$_{1-x}$,Sm$_{x}$)Ba$_{2}$Cu$_{3}$O$_{7-δ}$ ($x$=0, 0.1, 0.2 and 1.0) and YBa$_{2}$(Cu$_{1-y}$Zn$_{y}$)$_{3}$O$_{7-δ}$($y$=0.0071) as functions of temperature and magnetic field (along the c axis). For comparison, the temperature dependence of $κ_{ab}$ for as-grown crystals with the corresponding compositions are presented. The nonlinear field dependence of $κ_{ab}$ for all crystals was observed at relatively low fields near a half of $T_{c}$. We make fits of the $κ(H)$ dat…
Phase Stability of Lead Phosphate Apatite Pb$_{10-x}$Cu$_{x}$(PO$_{4}$)$_{6}$O, Pb$_{10-x}$Cu$_{x}$(PO$_{4}$)$_{6}$(OH)$_{2}$, and Pb$_{8}$Cu$_{2}$(PO$_{4}$)$_{6}$
本文用 DFT 总能量与声子计算评估 LK-99 相关磷酸铅磷灰石的稳定性，发现 Cu 取代相不在基态凸包且结构存在声子失稳，并预测新相及可行合成路径。
We use first-principles calculations to investigate the stability of bi-axially strained \textit{Pnma} perovskite CaMnO$_3$ towards the formation of oxygen vacancies. Our motivation is provided by promising indications that novel material properties can be engineered by application of strain through coherent heteroepitaxy in thin films. While it is usually assumed that such epitaxial strain is accommodated primarily by changes in intrinsic lattice constants, point defect formation is also a likely strain relaxation mechanism. This is particularly true at the large strain magnitudes ($>$4%) whi…
We study the electronic and structural properties of the low-temperature ordered phase of hydrogen-bonded molecular conductors, $κ$-D$_3$(Cat-EDT-TTF)$_2$ and its selenium-substituted analog $κ$-D$_3$(Cat-EDT-ST)$_2$, by means of first-principles density functional theory~(DFT) calculations. In these compounds, the charge ordering in the $π$-electron system is coupled with the ordering of the displacements in the deuteriums forming the hydrogen-bond, equally shared by two oxygens in the high-temperature phase. While the structural optimization within the standard DFT method based on the genera…
We present a study of the thickness dependence of magnetism and electrical conductivity in ultra thin La0.67Sr0.33MnO3 films grown on SrTiO3 (110) substrates. We found a critical thickness of 10 unit cells below which the conductivity of the films disappeared and simultaneously the Curie temperature (TC) increased, indicating a magnetic insulating phase at room temperature. These samples have a TC of about 560 K with a significant saturation magnetization of 1.2 +- 0.2 muB/Mn. The canted antiferromagnetic insulating phase in ultra thin films of n< 10 coincides with the occurrence of a higher s…
We have examined whether the Co ions crystallographically substitute on the Ti sites in rutile and anatase Ti_{1-x}$Co$_{x}$O$_{2-delta}$ thin films that exhibit room-temperature ferromagnetism. Intensities of the x-ray Bragg reflection from the films were measured around the $K$-absorption-edge of Co. If the Co ions randomly substitute on the Ti sites, the intensity should exhibit an anomaly due to the anomalous dispersion of the atomic scattering factor of Co. However, none of the anatase and rutile samples did exhibit an anomaly, unambiguously showing that the Co ions in Ti$_{1-x}$Co$_{x}$O…
Investigation of the oxygen-deficient 112-type ordered oxides of the type LnBaCoMnO5+δ(Ln = Nd, Eu) evidences certain unusual magnetic behavior at low temperatures, compared to the LnBaCo2O5+δcobaltites. One observes that the substitution of manganese for cobalt suppresses the ferromagnetic state and induces strong antiferromagnetic interactions. Importantly, NdBaCoMnO5.9 depicts a clear paramagnetic to antiferromagnetic type transition around 220 K, whereas for EuBaCoMnO5.7 one observes an unusual magnetic behavior below 177 K which consists of ferromagnetic regions embedded in an antiferroma…
$β$-Ga$_2$O$_3$(001) surface reconstructions from first principles and experiment
Institut für Physik and CSMB, Humboldt-Universität zu Berlin（柏林洪堡大学物理系与CSMB）；The Fritz-Haber-Institut der Max-Planck-Gesellschaft（马克斯·普朗克学会弗里茨·哈伯研究所）；Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V.（柏林研究联合体莱布尼茨保罗·德鲁德固体电子学研究所）；Leibniz-Institut für Kristallzüchtung (IKZ)（莱布尼茨晶体生长研究所）
From Disorder to Function: Entropy-Engineered Broadband Photonics with Ion-Transport-Stabilized Spectral Fidelity
Huazhong University of Science and Technology (HUST)（华中科技大学）；Guangdong HUST (Huazhong University of Science and Technology) Industrial Technology Research Institute（华南理工大学（华中科技大学）广东工业技术研究院）；University of Science and Technology of China（中国科学技术大学）；Artificial Intelligence for Science Institute（人工智能科学研究所）；Wuhan National Laboratory for Optoelectronics (WNLO)（武汉光电国家研究中心）；Fudan University（复旦大学）；Institute of Applied Physics and Computational Mathematics（应用物理与计算数学研究所）；Peking University（北京大学）；Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences（中国科学院上海有机化学研究所）
A series of new Sr2-xBaxCuO3+y (0 x 0.6) superconductors were prepared using high-pressure and high-temperature synthesis. A Rietveld refinement based on powder x-ray diffraction confirms that the superconductors crystallize in the K2NiF4-type structure of a space group I4/mmm similar to that of La2CuO4 but with partially occupied apical oxygen sites. It is found that the superconducting transition temperature Tc of this Ba substituted Sr2CuO3+y superconductor with constant carrier doping level, i.e., constant d, is controlled not only by order/disorder of apical-O atoms but also by Ba content…
Density functional theory and molecular dynamics simulations have been used to optimize the structure of nanowires of SiO2. The starting structures were based on b-cristobalite, orthotridymite, b-tridymite, and rutile crystals. The analysis of the electronic structure has been validated by many-body perturbation calculations using the G0W0 and GW + Bethe-Salpeter equation approximations, in order to account for quasi-particle and excitonic effects. The calculations indicate that many of these nanowires have semiconducting character, while the corresponding bulk solids are insulators. In the ca…
We report on structural, magnetic and electronic properties of Co-implanted TiO2 rutile single crystals for different implantation doses. Strong ferromagnetism at room temperature and above is observed in TiO2 rutile plates after cobalt ion implantation, with magnetic parameters depending on the cobalt implantation dose. While the structural data indicate the presence of metallic cobalt clusters, the multiplet structure of the Co L3 edge in the XAS spectra gives clear evidence for a substitutional Co 2+ state. The detailed analysis of the structural and magnetic properties indicates that there…
The connection between noncentrosymmetric materials' structure, electronic structure, and bulk photovoltaic performance remains not well understood. In particular, it is still unclear which photovoltaic (PV) mechanism(s) are relevant for the recently demonstrated visible-light ferroelectric photovoltaic (K,Ba)(Ni,Nb)O$_{3-δ}$. In this paper, we study the bulk photovoltaic effect (BPVE) of (K,Ba)(Ni,Nb)O$_{3-δ}$ and KNbO$_{3}$ by calculating the shift current from first principles. The effects of structural phase, lattice distortion, oxygen vacancies, cation arrangement, composition, and strain…
Coordination Engineering of Dual-Atom Catalysts for Overall Water Splitting: Mechanistic Insights from Constant-Potential First-Principles and Machine Learning
Anhui Province Key Laboratory of Intelligent Computing and Applications, College of Physics and Electronic Engineering, Huaibei Normal University（淮北师范大学物理与电子工程学院安徽省智能计算与应用重点实验室）；Huaibei Key Laboratory for Advanced Thin Film Materials and Technology, Huaibei Normal University（淮北师范大学淮北先进薄膜材料与技术重点实验室）
First principles study of chalcogen vacancy effect on the optoelectronic and photocatalytic properties of transition metal dichalcogenides monolayers
Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague（布拉格捷克理工大学电气工程学院控制工程系）；Engineering Materials & nCATS, FEE, University of Southampton（南安普顿大学电气工程学院工程材料与nCATS）
