Ti Interface Research Articles

Joining Ti-based metallic glass and crystalline titanium by magnetic pulse welding

Due to low thermal stability and limited critical size, metallic glasses (MGs) are frequently considered for reinforcing composites. The production technology of composites should provide the minimum heat input to preserve the disordered structure of MGs. In this study, the solid-state magnetic pulse welding (MPW) was used to join crystalline titanium and Ti-based MG. The amorphous structure of the MG layer after MPW was confirmed by synchrotron X-ray radiation diffraction (XRD), ultra-small-angle X-ray scattering (uSAXS), and transmission electron microscopy (TEM). Crystalline particles were found only in the mixing zones subjected to the strongest heating during welding. The average size of the crystalline precipitates was about 25 nm, and their phase composition corresponded to a-Ti. In addition to Ti particles, titanium oxides and nitrides could form at the interface of Ti and MG layers during MPW.

Ab Initio Study of HfO2/Ti Interface VO/Oi Frenkel Pair Formation Barrier and VO Interaction With Filament

Frenkel pair (FP) formation at HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ti interface and oxygen vacancy interaction with the filament in HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ti-based resistive random access memory (ReRAM) are the important mechanisms in the ReRAM operations. In this article, the formation barriers, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{A}$ </tex-math></inline-formula> , and formation energies of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{O}/{O}_{i}$ </tex-math></inline-formula> FP across the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ti interface with and without preexisting vacancy are calculated using the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ab initio</i> tool under zero external electric field. It is found that both the formation barrier and energy can be increased or decreased due to a preexisting oxygen vacancy. The spread of the effect increases inversely with the distance between the FP and the preexisting vacancy. A compact model is then proposed. The parallel migration barrier of an oxygen vacancy at the nearest and the second nearest neighbors (NNs) of a filament is also studied. It is found that the second NN has the lowest barrier due to its ability to retain a +2 charge state. The merging and dissolution of an oxygen vacancy with a filament (equivalent to perpendicular migration) is found to have a similar behavior that +2 states enhance the interaction. It is found that the fourfold coordinated oxygens (4C) and threefold coordinated oxygens (3C) filaments behave similarly during dissolution. However, 4C and 3C filaments prefer merging with 4C and 3C vacancy, respectively. The barrier of merging a +2 4C vacancy with a 4C filament is only 0.56 eV. The data and model obtained from this study may be used to implement device-level simulators, such as kinetic Monte Carlo (KMC) simulators, for ReRAM.

Evaluation of Cu-Ti dissimilar interface characteristics for wire arc additive manufacturing process

PurposeThe purpose of this research is to show the characteristics of a Cu–Ti dissimilar interface produced by a wire arc-based additive manufacturing process. The purpose of this research was to determine the viability of the Cu–Ti interface for the fabrication of functionally graded structures (FGS) using the wire arc additive manufacturing (WAAM) process.Design/methodology/approachThis paper used the WAAM process with variable current vis-à-vis heat input to demonstrate multiple Ti-6Al-4V (Ti64) and C11000 dissimilar fabrications. The hardness and microstructure of the dissimilar interfaces were investigated thoroughly. The formation of Cu–Ti intermetallic at the Ti64/Cu fusion interface is been revealed by scanning electron microscopy and energy dispersive X-ray analysis, while X-ray diffraction was used to identify various Cu–Ti intermetallic phases. The effect of microstructure on interfacial sensitivity and hardness are also investigated.FindingsThe formation of CuTi intermetallic and the β-phase transformation in Ti-6Al-4V are found to be heat input dependent. The Cu diffusion length increases as the heat input for Ti64 deposition increases, resulting in a greater Cu–Ti intermetallic thickness. The Cu–Ti interface properties improve when the heat input is less than approximately 250 J/mm or the deposition current is less than 90 A. The microhardness ranges from 55 to 650 HV from the Cu-side to the interface and from 650 to 350 HV from the interface to the Ti-side. Higher current increases interface hardness, which increases brittleness and makes the interface more prone to interfacial cracking.Originality/valueNonlinear components are needed for a variety of extreme engineering applications, which can be met by FGS with varying microstructure, composition and properties. FGS produced using the WAAM process is a novel concept that requires further investigation. Despite numerous studies on Ti-clad Cu, information on Cu–Ti interface characteristics is lacking. Furthermore, the suitability of the WAAM process for the development of Cu–Ti FGS is unknown. As a result, the goal of this research article is to fill these gaps by providing preliminary information on the feasibility of developing Cu–Ti FGS via the WAAM process.

CO2 methanation boosted by support-size-dependent strong metal-support interaction and B–O–Ti component

Strong metal-support interaction (SMSI) has a great impact on the activity and selectivity of heterogeneous catalysts, which was usually adjusted by changing reduction temperature or processing catalyst in different atmosphere. However, few researches concentrate on modulating SMSI through regulating the structure of the support. Herein, we show how changing the surface environment of the anatase TiO2 (B–TiO2) can be used to modulate the SMSI. The moderate TiOx overlayer makes the Ni metal highly dispersed on the high specific surface area of support, resulting in a substantially enhanced CO2 methanation rate. Besides, a novel phenomenon was observed that boron dopants promote the formation of the B–O–Ti interface site, enhancing the catalytic performance of CO2 hydrogenation. DFT calculations confirm that the B–O–Ti structure facilitates the activation of CO2 and further hydrogenation to methane.

Large-Scale Integration of a Zinc Metasilicate Interface Layer Guiding Well-Regulated Zn Deposition.

Uneven distribution of electric fields at the electrolyte-anode interface and associated Zn dendrite growth is one of the most critical barriers that limit the life span of aqueous zinc-ion batteries. Herein, new-type Zn-A-O (A = Si, Ti) interface layers with thin and uniform thickness, porosity, and hydrophilicity properties are developed to realize homogeneous and smooth Zn plating. For ZnSiO3 nanosheet arrays on Zn foil (Zn@ZSO), their formation follows an "etching-nucleation-growth" mechanism that is confirmed by a well-designed Zn-island-based identical-location microscopy method, the geometric area of which is up to 1000 cm2 in one-pot synthesis based on a low-temperature wet-chemical method. Guided by the structural advantages of the ZSO layer, the Zn2+ flux gets equalized. Besides ultralow polarization, the life spans of symmetric cells and full cells coupled with a high-mass-loading K0.27 MnO2 ·0.54H2 O (8mg cm-2 ) cathode, are increased by 3-7 times with the Zn@ZSO anode. Moreover, the large-scale preparation of Zn@ZSO foil contributes to a 0.5 Ah multilayer pouch cell with high performance, further confirming its prospects for practical application.

Extraordinary Equilibrium Isotope Effects of H to D at the Interfaces of Ni and Ti/Alkaline Solutions

The Frumkin adsorption isotherms of hydrogen (H or 1H) and deuterium (D or 2H) and the related equilibrium isotope effects (EIEs) of H to D at the Ni and Ti/0.1 M KOH (H2O and D2O) solution interfaces were determined using the phase-shift method and electrochemical impedance spectroscopy. Note that both the Frumkin adsorption isotherms and EIEs are not readily determined using conventional methods. We experimentally observed the unusual EIEs at the Ni and Ti interfaces. The unusually large value of EIE at the Ni interface is 39.2 to 289.7 and increases with increasing the fractional coverage (0 ≤ θ ≤ 1). The value of EIE at the Ni interface is much greater than that at the Pt-group metal interfaces. On the other hand, the value of EIE at the Ti interface is 1.1 and closes to unity. The isotope effects of H and D at the Ti interface are negligible. The Ni and Ti are efficient and stable electrocatalysts for maximizing and minimizing the isotope effects of H and D in the Volmer steps, respectively. The extraordinary EIEs at the Ni and Ti/alkaline solution interfaces can be used to evaluate and trace the water electrolysis and movement in water systems.

Bond formation at polycarbonate | X interfaces (X = Ti, Al, TiAl) probed by X-ray photoelectron spectroscopy and density functional theory molecular dynamics simulations

To investigate the bond formation at polycarbonate (PC) | X interfaces (X = Ti, Al, TiAl) by X-ray photoelectron spectroscopy, thin metallic layers were deposited onto PC substrates by direct current magnetron sputtering. Additionally, changes in the chemical state of the polymer were studied systematically by density functional theory molecular dynamics simulations of a PC dimer interacting with the corresponding metallic surfaces. These predictions were confirmed by experiments, indicating a higher reactivity at PC | Ti interfaces: Ti reacts with all functional groups of PC, forming numerous interfacial CTi and (CO)Ti bonds, whereas Al exhibits selective reactivity as only (CO)Al bonds with the carbonate group are formed. However, integrated crystal orbital Hamilton population (ICOHP) calculations indicate a significantly higher interfacial bond strength for (CO)Al bonds compared to (CO)Ti and CTi bonds (ICOHP differences up to 3.1 eV). By multiplying the experimentally determined relative interfacial bond concentration with the theoretically determined maximum bond strength as an indicator for adhesion, the PC | Ti interface exhibits a ∼1.9 and ∼1.4 times larger value compared to the PC | Al and the PC | TiAl interface, respectively. Thus, Ti thin films are the preferential choice as adhesion layers for PC.

Partially biodegradable Ti Mg composites prepared by microwave sintering for biomedical application

Partially biodegradable TiMg composites were prepared by microwave sintering using the elemental Ti and Mg powders. The effect of Mg contents on the microstructure, mechanical properties, corrosion resistance, Mg degradation behavior of the TiMg composites was investigated. The number of block Mg distributed over the Ti matrix gradually increases with increasing the Mg contents, in which the Mg and Ti form the metal-metal composite, and the interface of Mg and Ti is well bonded. The compressive strength of the TiMg composites gradually decreases from 625 MPa to 357 MPa with increasing the Mg contents, while the elastic modulus varies little, ranged from 4.8 GPa to 5.7 GPa. The corrosion resistance of the TiMg composites in SBF solution gradually decreases with increasing the Mg contents, resulting in the increase of hydrogen evolution amount. According to the electrochemical impedance spectroscopy, the corrosion and degradation of the TiMg composites in SBF solution can be divided into three stages: the corrosion and degradation of Mg, the formation of Mg(OH)2 layer and the dissolve of Mg(OH)2 layer coupled with the formation of hydroxyapatite layer.

Effect of thickness of transition layer on the microstructure and properties of the titanium/stainless steel welds with oscillating laser

Titanium (Ti)/stainless steel weld joints with copper (Cu) transition layer thicknesses of 0.2, 0.4, and 0.6 mm were studied through combined experimental and finite element methods. Then, the formation mechanism and distribution of the Ti–Cu compounds (intermetallic compounds, IMCs) were analyzed. The results showed that the thicknesses of the Ti–Cu IMCs decreased with increasing thickness of the Cu layer, and the tensile strength and elongation increased when welding was conducted under a ring oscillation laser with a spot diameter of 0.3 mm, an oscillating diameter of 0.1 mm, a welding speed of 220 cm/min, and a laser power of 2000 W. In the 0.2 and 0.4 mm Cu layers, Ti–Fe IMCs appeared in the welds, and the thicknesses of the Cu–Ti IMC layers were 60 and 30 μm, respectively. When the 0.6 mm Cu transition layer was used, a pure Cu layer appeared in the weld, which effectively inhibited the formation of Ti–Fe IMCs. The thickness of the Cu–Ti IMC layer was reduced owing to the faster cooling rate at the Cu–Ti interface. Furthermore, the Cu4Ti phase was distributed in a thin area of 15 μm, which improved the mechanical properties of the welded joint and allowed the tensile strength to reach 330 MPa. Compared to the welding joints with Cu layer thickness less than or equal to laser irradiation width, the joints with Cu layer thickness larger than laser irradiation width have a significantly improved tensile strength.

Structural Transformations at the Interface of Explosively Welded Al and Ti: Experimental Research and Numerical Simulation

In this work, the features of plastic deformation of titanium and aluminum plates under high-speed impact conditions were studied. The structure and phase composition of the explosively welded bimetal were analyzed using both scanning and transmission electron microscopy. The deformation and heating of titanium and aluminum under high-velocity impact were simulated using the smoothed particle hydrodynamics method. The features of shockwave and deformation-thermal processes during the collision of plates were described. The phase composition of the weld and heat-affected zone have been studied. The contribution of the welded plates to the jet formation is estimated.

Thermal stability study of Weyl semimetal WTe&lt;sub&gt;2&lt;/sub&gt;/Ti heterostructures by Raman scattering

Weyl semimetal Td-phase WTe&lt;sub&gt;2&lt;/sub&gt;, a novel topological matter, possesses a strong spin-orbit coupling and non-trivial topological band structure, and thus becomes a very promising superior spin current source material. By constructing the WTe&lt;sub&gt;2&lt;/sub&gt;/Ti heterostructures, the issue that the ferromagnetic layer with perpendicular magnetic anisotropy cannot be directly prepared on WTe&lt;sub&gt;2&lt;/sub&gt; layer can be well addressed, and meet the requirements for high-performance spin-orbit torque devices. To be compatible with the semiconductor technology, the device integration usually involves a high temperature process. Therefore, the thermal stability of WTe&lt;sub&gt;2&lt;/sub&gt;/Ti is critical for practical device fabrication and performance. However, the thermal stability of WTe&lt;sub&gt;2&lt;/sub&gt;/Ti interface has not been very clear yet. In this work, the micro-Raman scattering technique is used to systematically study the WTe&lt;sub&gt;2&lt;/sub&gt;/Ti interface annealed at different temperatures. It is found that the thermal stability of the interface between WTe&lt;sub&gt;2&lt;/sub&gt; and Ti is related to the thickness of WTe&lt;sub&gt;2&lt;/sub&gt; flake; appropriate increase of the WTe&lt;sub&gt;2&lt;/sub&gt; thickness can lead to the improvement of thermal stability in WTe&lt;sub&gt;2&lt;/sub&gt;/Ti heterostructures. In addition, high temperature annealing can cause a significant interfacial reaction. After annealed at 473 K for 30 min, the interface between WTe&lt;sub&gt;2&lt;/sub&gt; (12 nm) and Ti changes dramatically, leading to the formation of Ti-Te interface layer. This observation is highly consistent with the observations by high-resolution transmission electron microscopy and the elemental analysis results as well. This study will provide useful information for further exploring the influence of the WTe&lt;sub&gt;2&lt;/sub&gt;/Ti interface on the spin-orbit torque effect, and greatly invigorate the research area of energy efficient spintronic devices based on WTe&lt;sub&gt;2&lt;/sub&gt; and other novel topological materials.

Study on interface and mechanical properties of Ti–Al3Ti metal-intermetallic laminate reinforced by Ni-plated woven carbon fibers

Ni plated continuous woven carbon fibers (Ni–Cf) reinforced Ti–Al3Ti metal-intermetallic laminate composites (Ni-CfR-MIL) were prepared by electroplating assisted hot pressing sintering (HP). Scanning electron microscopy (SEM) was used to characterize the effect of Ni plating on the Cf surface, structure and interface of the composites. The diffusion distribution of elements was observed by using electron probe microscope analyser (EPMA) and energy dispersive spectrometer (EDS). Transmission electron microscopy (TEM) was used to observe and calibrate the interface in nanometer scale. The experimental results show that the interior of Cf bundle is completely infiltrated by Al. The Ni plating can promote the infiltration between Al and Cf, inhibit the interface reaction between Al and C, reduce the formation of harmful phase Al4C3 at the interface, and improve the bonding strength of Cf and matrix. There are diffusion layer I(Al3Ti) and diffusion layer II(Al13Fe4 & Al3Ni) in the material. Al4C3, Al13Fe4 and Al3Ni phases are formed by interfacial reaction during HP, and diffusion phase Al3Ni is precipitated in the Al3Ti layer near Ti layer. The tensile strength of Ni-CfR-MIL is 596Mpa and the fracture strain is 8.94%, both of which are better than that of Ti–Al3Ti MIL without fiber. The bending strength of Ni-CfR-MIL reaches 1101Mpa and the failure strain is 2.33%, which are 3.2 times and 1.9 times that of Ti–Al3Ti MIL respectively. By observing the crack of the failure fracture, the cause of performance improvement was analyzed.

Molecular dynamics investigation of atomic mixing and mechanical properties of Al / Ti interface

With the urgent lightweight demand in the aerospace engineering and transportation industries, Al / Ti composite structures have attracted much interest due to their excellent performances compared with conventional materials. Computational simulations have contributed to the understanding of both fundamental and practical aspects of fabrication of such composites and studying of their properties. The present work reports the results of studies based on molecular dynamics simulations on the mechanical properties of an Al / Ti composite obtained by compression combined with shear strain. Tensile properties of a nanosized Ti / Al composite consisting of two single crystals obtained after different compression rates are analyzed. The loading scheme applied in the present work is a simplification of the scenario experimentally realized previously to obtain Al-matrix composites. It is confirmed that uniaxial compression combined with shear deformation is an effective way to obtain the composite structure since severe plastic deformation facilitates the diffusion process. The results indicated that a symmetrical atomic movement took place in the Ti / Al interface during deformation. However, Al atoms diffuse into the Ti block easier than Ti atoms into the Al block. Tensile tests showed that fracture took place in the Al part of the final composite sample, which means that the interlayer region where the mixing of Ti and Al atoms is observed is stronger than the pure Al part.

Effect of Ti-doping on peeling resistance of primary M7C3 carbides in hypereutectic Fe[sbnd]Cr[sbnd]C hardfacing coating and γ-Fe/M7C3 interfacial bonding strength

Alloying element Ti plays an important role in improving the mechanical properties of hypereutectic FeCrC hardfacing coating, but its peeling resistance have been neglected. Here, the hardness and wear rate of the hypereutectic FeCrC and FeCrCTi hardfacing coatings were measured. The crystal structure and orientation relationship of primary M7C3 carbide and eutectic austenite matrix were confirmed. Then, the interface properties of γ-Fe//M7C3(Ti) interface were calculated by first principles. The results show that the micro-Vickers and macroscopic Rockwell hardness of the FeCrCTi hardfacing coating are increased, and its wear rate is decreased from (4.33 ± 0.333) × 10−6 mm3/Nm to (3.64 ± 0.366) × 10−6 mm3/Nm. The Ti-doping can effectively inhibit the initiation and propagation of cracks and improve the peeling resistance of M7C3 carbide. Meanwhile, the orientation relationship of eutectic austenite/primary M7C3 carbide is γ-Fe(111)//(Cr, Fe)7C3(101¯0). Among CFe1, CrFe1 and FeFe1 interfaces, interface energy of FeFe1 model is the smallest (1.954 J/m2), and its adhesion work (Wad) is the largest (0.756 J/m2). Moreover, Wad of Ti-doped interface (4.123 J/m2) is larger than that of FeFe1 one (3.045 J/m2) after relaxed, which indicates Ti-doping is beneficial to enhance adhesive strength between γ-Fe//M7C3 interfaces, which improves the peeling resistance of M7C3 carbide.

Effect of heat input on interfacial characterization of the butter joint of hot-rolling CP-Ti/Q235 bimetallic sheets by Laser\u2009+\u2009CMT

Composite structures made of 2 mm-thick titanium and 10 mm-thick carbon steel are widely used in infrastructures such as long-distance gas transportation. However, cracking, which is caused by intermetallic compounds (ICs), is a dominate failure mode in welds of this structure. Thus, a common way to improve the in-service life of is reduce the number of ICs. In this paper, we employ a novel hybrid welding method to fabricate composite structures of TA2 titanium and Q235 carbon steel. Specifically, Ti and carbon steel is welded by laser and double Cold Metal Transfer (CMT) welding, respectively. The microstructure near the interface of Ti and steel is then examined using SEM, EBSD, EDS, with emphasis on the ICs in terms of chemical elements and morphologies. Results show that FeTi and Fe2Ti are the main ICs near the interface, and responsible for the failure of the welds. The effect of welding heat input on the formation of ICs is investigated as well. Results show that ICs are smaller when the heat input is low. Under low heat input circumstance, the tensile strength of the weld can reach up to 420 MPa.

Synthesis and study of highly dense and smooth TiN thin films

This study aims towards a systematic reciprocity of the tunable synthesis parameters - partial pressure of N2 gas, ion energy (Ei) and Ti interface in TiN thin film samples deposited using ion beam sputtering at ambient temperature (300 K). At the optimum partial pressure of N2 gas, samples were prepared with or without Ti interface at Ei = 1.0 or 0.5 keV. They were characterized using x-ray reflectivity (XRR) to deduce thickness, roughness and density. The roughness of TiN thin films was found to be below 1 nm, when deposited at the lower Ei of 0.5 keV and when interfaced with a layer of Ti. Under these conditions, the density of TiN sample reaches to 5.80(±0.03) g cm−3, a value highest hitherto for any TiN sample. X-ray diffraction and electrical resistivity measurements were performed. It was found that the cumulative effect of the reduction in Ei from 1.0 to 0.5 keV and the addition of Ti interface favors (111) oriented growth leading to dense and smooth TiN films and a substantial reduction in the electrical resistivity. The reduction in Ei has been attributed to the surface kinetics mechanism (simulated using SRIM) where the available energy of the sputtered species (<Esp>) leaving the target at Ei = 0.5 keV is the optimum value favoring the growth of defects free homogeneously distributed films. Secondary ion mass spectroscopy depth profile measurements confirm the uniform distribution of N and Ti across the depth of a sample. The electronic structure of samples was probed using N K-edge and Ti L-edge absorption spectroscopy and the information about the crystal field and spin-orbit splitting confirmed TiN phase formation. In essence, through this work, we demonstrate the role of <Esp> and Ti interface in achieving highly dense and smooth TiN thin films with low resistivity without the need of a high temperature or substrate biasing during the thin film deposition process.

Interface-induced sign reversal of the anomalous Hall effect in magnetic topological insulator heterostructures

The Berry phase picture provides important insights into the electronic properties of condensed matter systems. The intrinsic anomalous Hall (AH) effect can be understood as the consequence of non-zero Berry curvature in momentum space. Here, we fabricate TI/magnetic TI heterostructures and find that the sign of the AH effect in the magnetic TI layer can be changed from being positive to negative with increasing the thickness of the top TI layer. Our first-principles calculations show that the built-in electric fields at the TI/magnetic TI interface influence the band structure of the magnetic TI layer, and thus lead to a reconstruction of the Berry curvature in the heterostructure samples. Based on the interface-induced AH effect with a negative sign in TI/V-doped TI bilayer structures, we create an artificial “topological Hall effect”-like feature in the Hall trace of the V-doped TI/TI/Cr-doped TI sandwich heterostructures. Our study provides a new route to create the Berry curvature change in magnetic topological materials that may lead to potential technological applications.

Diamond(001)–Si(001) and Si(001)–Ti(0001) interfaces: A density functional theory study

Peeling is considered to be the main technical obstacle for coating applications. There are many factors that affect the peeling process of coatings. The interfacial properties of the coating and substrate play a crucial role in the peeling process. In this study, the work of adhesion (Wad), interface energy (γi), and electronic structure of diamond (001)–Si(001) and Si(001)–Ti (0001) interface models have been investigated using first-principles calculations. The results indicate that the diamond (001)–Si(001) interface exhibits larger Wad and smaller γi values when compared with the Si(001)–Ti (0001) interface. However, the Wad of diamond–diamond, Si–Si, and Ti–Ti is 15.92, 4.92, and 3.84 J/m2, respectively. When compared with the two interface models, the Wad of Ti–Ti is the smallest, indicating that it will be the first to undergo deformation during the shear process. In addition, analysis of the charge density difference and density of states revealed that the interfacial Ti–Si bond is a covalent–metallic bond, which is much weaker than the Si–C bond (covalent bond), and therefore, the Si(001)–Ti (0001) structure is more inclined to delaminate.

Selection of interfacial metals for Si3N4 ceramics by the density functional theory

Si3N4 has high mechanical strength and thermal cycling resistance, which can ensure reliability of electronic substrates under extreme environment. To enhance the wettability of ceramics and metal during the bonding process, it is necessary to use active metal. In this paper, charge density difference, density of sates and Bader charge of Si3N4 interfaces with Ti, Cr and Ni are respectively studied by first principles calculation. Results suggest that the electron transfer at the Si3N4(112¯0)/Ti(0001) interface is sufficient and the orbital hybridization of N and Ti is strong, indicating that it is the optimal interface between Si3N4 ceramics and metals.

Similarities and differences between nickelate and cuprate films grown on a SrTiO3 substrate

The recent discovery of superconductivity in Sr-doped NdNiO$_2$ films grown on SrTiO$_3$ started a novel field within unconventional superconductivity. To understand the similarities and differences between nickelate and cuprate layers on the same SrTiO$_3$ substrate, here based on the density functional theory we have systematically investigated the structural, electronic, and magnetic properties of NdNiO$_2$/SrTiO$_3$ and CaCuO$_2$/SrTiO$_3$ systems. Our results revealed a strong lattice reconstruction in the case of NdNiO$_2$/SrTiO$_3$, resulting in a polar film, with the surface and interfacial NiO$_2$ layers presenting opposite displacements. However, for CaCuO$_2$/SrTiO$_3$, the distortions of those same two CuO$_2$ layers were in the same direction. In addition, we found this distortion to be approximately independent of the studied range of film thickness for both the nickelate and cuprates films. Furthermore, we also observed a two-dimensional electron gas at the interface between NdNiO$_2$ and SrTiO$_3$, caused by the polar discontinuity, in agreement with recent literature. For NdNiO$_2$/SrTiO$_3$ the two-dimensional electron gas extends over several layers, while for CaCuO$_2$/SrTiO$_3$ this electronic rearrangement is very localized at the interface between CaCuO$_2$ and SrTiO$_3$. The electronic reconstruction found at the interface involves a strong occupation of the Ti $3d_{xy}$ state. In both cases, there is a significant electronic charge transfer from the surface Ni or Cu layers to the Ti interface layer. The interfacial Ni and Cu layer is hole and electron doped, respectively. By introducing magnetism and electronic correlation, we observed that the $d_{3z^2-r^2}$ orbital of Ni becomes itinerant while the same orbital for Cu remains doubly occupied, establishing a clear two- vs one-orbital active framework for the description of these systems.