Segregation Of Atoms Research Articles

Role of threshold stress in creep of IN740H, a γ′-lean Ni-based superalloy

IN740H, a Ni-based superalloy comprising a low-volume fraction of γ′, is a candidate material to be used over long periods at high temperatures and stresses, as conditions prevalent in advanced ultra-supercritical (AUSC) power plants. In this study, IN740H has been tested at temperatures above 700 °C to gain mechanistic insights into its high-temperature creep behavior. The material showed classic signatures of the presence of threshold stress, marked by observation of a high apparent creep stress exponent, n, (e.g., 10 at 750 °C) and a high apparent activation energy for creep, Qc (e.g., ∼545 kJ/mol), along with a rapid increase in n at lower stresses. Accounting for the threshold stress led to a decrease in the values of n and Qc to 4 and 280 kJ/mol, respectively. Furthermore, the transmission electron microscopy and atomic scale compositional analysis reveal the pinning of dislocations at γ-γ′ interface and segregation of Co, Cr and Mo atoms in the regions of γ-γ′ interface rich in dislocations. The above combination of n and Qc and the observation of dislocation pinning at the γ-γ′ interface indicate the dislocation climb over γ′ as the dominant creep mechanism in this γ′-lean Ni-based superalloy, with the detachment of dislocations from the γ-γ′ interface, augmented by the segregation of Co, Cr and Mo, as the mechanism responsible for the realization of the threshold stress. This work, thus, provides a new impetus to research on the long-term structural integrity of γ′-lean Ni-based superalloys exposed to extreme service conditions.

The tendency of V segregation in Pd/V(110) and Pd/V(100) surfaces induced by H adsorption

This study employs density functional theory-based calculations to investigate the tendency of V atom segregation in Pd/V(100) and Pd/V(110) surfaces upon adsorption of H at varying coverage (0.25, 0.50, 0.75, and 1.0 ML). Geometric, energetic, and electronic structure analyses were performed to elucidate the stability of H on the surfaces, the V atoms segregation tendency, and the interactions of atoms in the systems. By calculating the relative energies, we found that Pd atoms will favor residing in the topmost layer of pristine Pd/V. Segregation of V atom in pristine Pd/V(100) is more endothermic than in Pd/V(110). For H-Pd/V systems, a tendency of V segregation was observed for 0.50–1.0 ML H coverage on Pd/V(110). V atom segregation was not predicted in H-Pd/V(100). Due to the more endothermic V atom segregation process in pristine (100) than in (110) facet, a larger energy is necessary to induce V segregation by H adsorption in (100). The adsorption energies, charge density difference distributions, and density of states revealed the stronger H-V interaction compared to H-Pd interaction. Hence, H adsorption stabilizes the V atoms in the topmost layers and could induce V segregation in the surface.

Sensitization characteristics for type 445 ultra-pure ferritic stainless steel with an electrochemical reactivation method

The sensitization characteristics of type 445 ultra-pure ferritic stainless steel (FSS) under different aging conditions were investigated by the optimized double loop electrochemical potentiodynamic reactivation (DL-EPR) test and microstructure observation. The solution 2 mol L−1 H2SO4 + 0.01 mol L−1 KSCN +0.5 mol L−1 NaCl and a scan rate of 100 mV min−1 are suitable for the DL-EPR test of 445 FSS. With the change of aging temperature from 500 to 900 °C, the degree of sensitization (DOS) slightly increases at first and then decreases, which reaches a maximum value at about 700 °C. Under the aging condition at 700 °C for 10 min to 2 h, the DOS value gradually increases, but it is less than 3% due to the low intergranular corrosion susceptibility. The aging treatment at 700 °C results in the precipitation of Laves phase and (Nb, Ti)(C, N), but no Cr-carbides. The sensitization may be related to the segregation of Cr atoms around (Nb, Ti)-precipitates at the grain boundaries.

Composition templating for heterogeneous nucleation of intermetallic compounds.

Refinement of intermetallic compounds (IMCs) through enhancing heterogeneous nucleation during casting process is an important approach to improve the properties of aluminium alloys, which greatly increases the economy value of recycled Al-alloys. However, heterogeneous nucleation of IMCs is inherently more difficult than that of a pure metal or a solid solution. It requires not only creation of a crystal structure but also the positioning of 2 or more different types of atoms in the lattice with specific composition close to that of the nucleated IMCs. Previous understanding on heterogeneous nucleation is based on structural templating, usually considering the small lattice misfit at the interface between the nucleating solid and substrate. In this work, we proposed a hypothesis and demonstrated that composition templating plays a critical role in heterogeneous nucleation of IMCs. The experimental results revealed that segregation of Fe atoms on the AlB2 surface, i.e., the Fe modified AlB2 particle, provides the required composition templating and hence enhances heterogeneous nucleation of α-Al15(Fe, Mn)3Si2, resulting in a significant refinement of the α-Al15(Fe, Mn)3Si2 particles in an Al-5Mg-2Si-1.0Mn-1.2Fe alloy.

Competitive segregation to grain boundaries between Cr and Co in FeNiCrCo alloy

Alloying elements segregating to grain boundaries (GBs) is vital in determining structural stability and mechanical properties of alloys, especially in high‐entropy alloys (HEAs) that consist of multiple elements. However, some details remain unclear, such as the process of varied atoms (Cr and Co) cosegregation to GBs in FeNiCrCo alloy. Therefore, the competition and cooperation between Fe, Ni, Cr, and Co atoms segregating to GBs of FeNiCrCo alloy were investigated via molecular dynamic (MD) simulation. Five [110] symmetric tilt GBs of FeNiCrCo were applied to study the relation between the tendency of atomic segregation especially Cr and Co and GB characters including GB energy and GB excess free volume (GB excess volume). A competitive segregation phenomenon between Cr and Co atoms was discovered, which could be dominated by GB excess volume and different atomic radii among components.

First-principles study of behaviors of point defects in Mo-14 Re alloy

Molybdenum alloys with rhenium additions of 14 % (Mo-14 Re) are regarded as structural materials for advanced nuclear reactors. The performance of Mo-14 Re alloy under irradiation is crucial for its application. Irradiation performance is related to the behaviors of point defects produced by irradiation. The behaviors of point defects in Mo-14 Re alloy were investigated using first-principles methods in this work. Compared with the results in pure Mo alloy, the formation energy and the migration energy of vacancy in Mo-14 Re were both reduced, and the migration energy of interstitial dumbbell increased while the formation energy decreased in Mo-14 Re. In Mo-14 Re, vacancy preferred to form and diffuse faster in Re-enriched environment. Knowing the number of Re atoms in the 1NN (first nearest neighbor) shell of the vacancy and saddle point, the vacancy formation energy and migration energy can be estimated. Since the interstitial atom has a certain orientation, the distribution of the atoms around it is anisotropic. To estimate the interstitial formation energy, it was necessary to count the number of Re atoms at the tensile and compressive sites at the 1NN shell around the interstitial. The interstitial motion was three-dimensional (3D) in Mo-14 Re. At 1200 K, the diffusion coefficient of Re atom was a little higher than that of Mo atom, which could lead to the segregation of Re atoms at defect sinks and the formation of Re-enriched phase. It is possible to investigate the longer-term evolution of microstructure using cluster dynamics (CD) or kinetic monte carlo (KMC) techniques based on these results.

Electron Glass Phase with Resilient Zhang-Rice Singlets in LiCu_{3}O_{3}.

LiCu_{3}O_{3} is an antiferromagnetic mixed valence cuprate where trilayers of edge-sharing Cu(II)O (3d^{9}) are sandwiched in between planes of Cu(I) (3d^{10}) ions, with Li stochastically substituting Cu(II). Angle-resolved photoemission spectroscopy (ARPES) and density functional theory reveal two insulating electronic subsystems that are segregated in spite of sharing common oxygen atoms: a Cu d_{z^{2}}/O p_{z} derived valence band (VB) dispersing on the Cu(I) plane, and a Cu 3d_{x^{2}-y^{2}}/O 2p_{x,y} derived Zhang-Rice singlet (ZRS) band dispersing on the Cu(II)O planes. First-principle analysis shows the Li substitution to stabilize the insulating ground state, but only if antiferromagnetic correlations are present. Li further induces substitutional disorder and a 2D electron glass behavior in charge transport, reflected in a large 530meV Coulomb gap and a linear suppression of VB spectral weight at E_{F} that is observed by ARPES. Surprisingly, the disorder leaves the Cu(II)-derived ZRS largely unaffected. This indicates a local segregation of Li and Cu atoms onto the two separate corner-sharing Cu(II)O_{2} sub-lattices of the edge-sharing Cu(II)O planes, and highlights the ubiquitous resilience of the entangled two hole ZRS entity against impurity scattering.

Unphysical grain size dependence of lattice thermal conductivity in Mg3(Sb, Bi)2: An atomistic view of concentration dependent segregation effects

Grain boundary (GB) engineering is one of the most common strategies to reduce the lattice thermal conductivity and improve thermoelectric materials. However, in the case of the promising thermoelectric material Mg3(Sb1−xBix)2, an abnormal dependence of lattice thermal conductivity on grain size was observed at the concentration of x = 0.25, where smaller grain polycrystalline materials exhibited higher lattice thermal conductivity compared to larger grain materials. The proposed theory about the overestimation of lattice thermal conductivity in inhomogeneous materials with GBs cannot clarify the concentration dependence of this anomaly. Here we elucidate the interplay between segregation, concentration, and lattice thermal conductivity in Mg3(Sb1−xBix)2 alloys through atomistic simulations with a highly accurate machine learning interatomic potential. We find the largest segregation of Bi atoms to GBs in Mg3(Sb1−xBix)2 at the concentration of x = 0.25 for both twist and tilt GB structures due to the combination effects of site spectrality and solute interactions. Our molecular dynamic simulations demonstrate that the pronounced segregation of heavier Bi atoms, particularly at x = 0.25, leads to a substantial increase in the lattice thermal resistance at GBs, thus contributing to the degree of inhomogeneity. The concentration dependent segregation reveals the atomic origin of the observed unphysical inverse relationship between grain size and lattice thermal conductivity at the specific concentration of x = 0.25. These results highlight the need to design the alloy concentration to tune the atomic segregation and tailor the thermal properties of thermoelectric materials with GBs.

Evolution of bimodal-structure and achieving ultra-high yield strength in the as-extruded ZK70 alloy via Gd addition

Achieving ultra-high tensile yield strength over 400 MPa in RE modified Mg–Zn-based alloys using conventional thermomechanical processing is a challenging task. In this study, we successfully produced a Mg–7Zn–2Gd–0.5Zr (wt. %) alloy with exceptional strength through traditional hot-extrusion techniques. This alloy exhibits a tensile yield strength of 440 MPa and an acceptable ductility of 4.5%, surpassing a majority of previously reported Mg–Zn-RE-based alloys. Our findings demonstrate that the addition of Gd in Mg–Zn-based alloys effectively retards dynamic recrystallization (DRX) during extrusion, leading to the formation of a distinctive bimodal structure comprising approximately 13.8% coarse un-recrystallized (unDRXed) grains and about 86.2% fine DRXed grains. Furthermore, the alloying effect of Gd enhances particle density, including micron-sized particles and dynamic nano-precipitates. These dynamic precipitates play a crucial role in impeding dislocation movement during extrusion, thereby contributing to the formation of bimodal structure. Additionally, both nano-precipitates and segregation of Zn and Gd atoms towards grain boundaries facilitate the formation of fine DRXed grains through pinning effect. Consequently, the significantly increased tensile yield strength observed in our Gd-modified alloy can be attributed to multiple strengthening mechanisms: fine DRXed grains, strong texture exhibited by unDRXed grains, numerous dynamic precipitates, high-density residual dislocations, and co-segregation of solutes. However, the formation of bimodal structure worsens the yield asymmetry of the Gd-modified alloy due to its strong basal texture. These results provide a valuable insight for further development efforts aimed at achieving ultra-high-strength Mg–Zn-RE-based alloys.

Uncovering origin of grain boundary resistance to irradiation damage in NiCoCr multi-principal element alloys

Multi-principal element alloys (MPEAs) demonstrate significant promise as structural materials for nuclear energy equipment owing to their exceptional mechanical properties and radiation-resistant performances. In these alloys, the grain boundary (GB) serves as a crucial microstructure that typically mitigates irradiation damage by absorbing the irradiation-induced defect. However, the micromechanisms governing the anti-irradiation performance of GBs in MPEAs remain unclear. In this study, we investigate the irradiation defect production during collision cascade in the model NiCoCr bicrystal system through atomic simulations, aiming to unveil the atomic-scale origin of GB to resist irradiation damage in MPEAs. The results reveal that GBs effectively serve as sinks for irradiation defects in NiCoCr. The sink efficiency depends on the GB energetic state, including GB excess energy and defect segregation energy, as well as the energetic difference between interstitial and vacancy segregation. Statistical analysis identifies a universally exponent function between the defect absorption rate at GB and GB energetic state. In NiCoCr, the GB-disorder-induced-entropy increase leads to a biased reduction in interstitial segregation energy, narrowing the gap between interstitial and vacancy segregation energies by approximately 11 % compared to Ni. This improvement enhances the overall resistance of GBs to irradiation damage. Additionally, preferential segregation of Ni interstitial atoms is notably enhanced in NiCoCr, contributing to a high defect absorption rate at GBs. This study provides new insights into the resistance of GBs to irradiation defects in MPEAs and suggests GB engineering as an effective strategy for developing advanced alloys with enhanced radiation tolerance.

Inhomogeneity of microstructure evolution in stir zone of 2195Al thick-plate FSW joints

An appropriate friction stir welding (FSW) tool has been developed to perform high-quality joining of 12 mm thick Al-Li alloy plates. Threads and triple facets were machined on the stirring pin to improve the material flow. The differences in microstructure characteristics, recrystallization mechanisms, and precipitate evolution along the stir zone (SZ) thickness were systematically clarified. The results indicated that microstructures in SZ were refined by dynamic recrystallization (DRX) and showed an apparent top-to-bottom gradient distribution in grain size. The geometric topology of the stirring pin results in periodic ultrafine-grained bands throughout SZ. At the top and middle regions of SZ, high-density vacancies and dislocations were formed due to elevated temperature and strain rate, facilitating the precipitation of T1 (Al2CuLi) phases through a dislocation-induced heterogeneous nucleation mechanism. In comparison, icosahedral quasi-crystalline T2 (Al6Cu(Li, Mg)3) phases, which can be attributed to the segregation of atoms and high cooling rate, were detected along grain boundaries at SZ-bottom. Furthermore, the ultimate strength values of tensile specimens sectioned from the top, middle, and bottom parts of SZ are 452, 457, and 406 MPa, respectively. Studying the inhomogeneous microstructure and properties of welded joints provides a theoretical basis for manufacturing high-load components.

Grain boundaries-dominated migration failure of copper interconnect under multiphysics field: Insight from theoretical modeling and finite element analysis

As the feature size of Cu interconnects in microelectronic devices are miniaturized into micro- and even nano-scale, the effects of grain boundaries (GBs) on the electromigration (EM) failure become more and more obvious. It is of fundamentally importance to investigate the grain boundaries dominated failure mechanism and lifetime of Cu interconnects. In this work, the interconnection models containing different grain boundaries were constructed by using finite element simulations. The simulation results indicate that the current density at Cu grain boundaries is lower, but the current will be increased locally, when it is almost perpendicular to grain boundaries. However, the temperature is higher locally at grain boundaries. In the early stage of atomic diffusion, thermal migration and stress migration also occur near grain boundaries, resulting in significant atomic segregation near grain boundaries, particularly at the intersection of grain boundaries and near the inclined grain boundaries with small angles to the current direction. The atomic diffusion is considerably accelerated as the density of grain boundaries is increased, but is slowed down by poorly connected columnar grain boundaries.

Combined effect of interstitial-substitutional elements on dislocation dynamics in nitrogen-added austenitic stainless steels

Combined addition of interstitial-substitutional elements has been acknowledged to contribute to the increase in the strengths of steels. For further improvements in mechanical properties, their atomic-scale interaction mechanisms with dislocations are required to be examined. In this study, both high-resolution transmission electron microscopy and atom-probe tomography were used to correlate interstitial-substitutional elements with dislocation characteristics in austenitic stainless steels. Three types of dislocation core structures are identified and associated with their strain fields as well as N and Cr atoms in the N-added steels. It is revealed that N atoms interact elastically with the dislocations, followed by the segregation of Cr atoms via the chemical interaction between N and Cr atoms. This insight significantly improves the understanding of the multiple alloying mechanism in metallic materials such as interstitial alloys and high-entropy alloys.

Multiscale Length Structural Investigation and Thermoelectric Performance of Double-Filled Sr0.2Yb0.2Co4Sb12: An Exceptional Thermal Conductivity Reduction by Filler Segregation to the Grain Boundaries.

Among thermoelectric materials, skutterudites are the most prominent candidates in the mid-temperature range applications. In the multiple-filled Sr0.2Yb0.2Co4Sb12 skutterudite, with Sr and Yb as fillers, we have enhanced the thermoelectric performance of CoSb3 through the reduction of lattice thermal conductivity and the optimization of carrier concentration and electrical conductivity. The high-pressure synthesis of the double-filled derivative promotes filling fraction fluctuation. This is observed by high angular resolution synchrotron X-ray diffraction, showing a phase segregation that corresponds to an inhomogeneous distribution of the filler atoms, located at the 2a positions of the cubic space group Im3̅. In addition, scanning transmission electron microscopy (STEM) combined with EELS spectroscopy clearly shows a segregation of Sr atoms from the surface of the grains, which is compatible with the synchrotron X-ray powder diffraction results. Mean square displacement parameters analysis results in Einstein temperatures of ∼94 and ∼67 K for Sr and Yb, respectively, and a Debye temperature of ∼250 K. The strong effect on resonant and disorder scattering yields a significantly lower lattice thermal conductivity of 2.5 W m-1 K-1 at 773 K. Still, good weighed-mobility values were obtained, with high filling fraction of the Yb and Sr elements. This drives a reduced electrical resistivity of 2.1 × 10-5 Ω m, which leads to a peak zT of 0.26 at 773 K. The analysis and results performed for the synthesized (Sr,Yb)-double filled CoSb3, shed light on skutterudites for potential waste-heat recovery applications.

First-principles investigation of the Mg, Cu segregation at Al Σ5 (310) and Σ9 (221) symmetrical tilt grain boundaries

The segregation of alien solute atoms at grain boundaries (GBs) in nanocrystalline materials can dramatically affect their macroscopic properties. As important solutes in Al alloys, Mg and Cu atoms have been experimentally observed to segregate at GBs, which would render a significant impact on the material. In this work, first-principles calculations were used to conduct a systematic and comprehensive investigation to reveal the segregation behavior of Mg and Cu atoms at Al Σ5 (310) and Σ9 (221) GBs and its effect on GB properties. The negative segregation energy demonstrates that both Mg and Cu have a strong tendency to segregate to the Al GBs. Moreover, the segregation of Mg and Cu atoms can reduce the GB energy, indicating an increased thermodynamic stability of the GBs. Mechanical properties are explored by a combination of canonical Griffith fracture model with ab-initio tensile test method. Results reveal that the doped Mg will embrittle both GBs due to the elongation of interatomic bonds and depletion of charge density across the GBs. Contrarily, the segregated Cu contributes greatly to enhancing the GB strength by creating strong Cu-Al bonds with surrounding Al at GBs. Besides, the increased tensile separation displacement of GBs with Cu segregation also suggests an improved resistance to fracture, especially the Σ9 (221) GB. This work provides a theoretical understanding for the changes in microscopic properties of Al GBs caused by Mg and Cu segregation from an atomic and electronic level.

Interfacial Kagome lattice transitions induced by segregation of solute atoms

Interfacial structural transformations arising from solute segregation play a crucial role in the performance of materials. However, these micro-transitions are often difficult to reveal due to their buried nature. Here, in a typical Mg-rare-earth model system, we present the discovery of interfacial Kagome lattice transitions triggered by segregation of solutes coupled with bi-crystalline lattice interactions, in three types of partially coherent tilt grain boundaries (GBs), using atomic-resolution scanning transmission electron microscopy observations plus theoretical calculations. The results demonstrate that the minimization of GB elastic strain is responsible for the selective segregation of solutes at interfacial specific sites, resulting in a confined phase transition of the embedded triangular-quadrilateral (101¯1)Mg lattice to a topological hexagonal-triangular Kagome lattice via atomic shuffling. Furthermore, the pressure-temperature conditions that trigger such interfacial Kagome lattice transitions have also been determined. These findings not only enrich the transition pathways formed by the Kagome lattice but also provide a bottom-up approach for investigating interfacial structural transformations induced by solute/impurity segregation in polycrystalline materials.

Critical Examination of the Representativeness of Austenite Grain Growth Studies Performed In Situ Using HT-LSCM and Application to Determine Growth-inhibiting Mechanisms

This contribution critically addresses the potential of HT-LSCM experiments for in situ observations of austenite grain growth (AGG). By quantifying AGG for various alloys, the impact of impurity induced solute drag effects (SDE) and second phase precipitation Zener pinning forces (PZ) on AGG can be estimated. Also the grain boundary mobility (GBM) can be determined. The measured arithmetic mean of the time-resolved grain size distributions as a function of temperature and chemical composition is the most important value for quantification. The obtained data is then used to contribute to mathematical models of classical grain growth theory and to allow conclusions on parametrization of SDE and PZ. In this contribution, grain size measurements at the sample surface (in situ and ex situ) are compared with ex situ bulk measurements and experiments on grain growth in the single-phase austenite region (γ-Fe) under isothermal annealing conditions at different temperatures are presented. Grain growth results include high-purity Fe (Fe > 99.98%), binary Fe‑P, Fe‑C, and quaternary Fe-C-Nb‑N systems. For the alloys investigated, it is assumed that grain growth in high-purity Fe occurs without the influence of solute drag or precipitation mechanisms. In Fe‑P, it is shown that grain growth is inhibited by the segregation of impurity atoms at the grain boundaries (GB), which allows conclusions to be drawn about the influence of SDE. In the case of Fe-C-Nb‑N systems, the influence of Nb(C,N) precipitation on grain growth due to Zener pinning forces is presented.

Hydrogen on screw dislocation in Fe and W: Existence of 3D-compound and exotic segregation profile

We present the study of hydrogen atom segregation on screw dislocation in Fe and W metals by means of rigid lattice Monte Carlo simulations using interaction energies obtained from ab initio calculations. These interaction energies are attractive or repulsive depending on direction and distance. This high interaction anisotropy leads to the formation of a 3D compound for both iron and tungsten. A second consequence is that, within a given temperature range, hydrogen enrichment is greater at the outer than at the innermost sites of the dislocation. This unusual behavior is only observed for iron. We propose a mean-field model that accounts for the ordering phenomenon to explain the results and the differences between the two metals.

Microstructure Evolution during High-Pressure Torsion in a 7xxx AlZnMgZr Alloy.

A homogenized, supersaturated AlZnMgZr alloy was processed via severe plastic deformation (SPD) using a high-pressure torsion (HPT) technique for different revolutions at room temperature to obtain an ultrafine-grained (UFG) microstructure. The microstructure and mechanical properties of the UFG samples were then studied using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and tensile and hardness measurements. The main purpose was to study the effect of shear strain on the evolution of the microstructure of the investigated alloy. We found a very interesting evolution of the decomposed microstructure in a wide range of shear strains imposed by HPT. While the global properties, such as the average grain size (~200 nm) and hardness (~2200 MPa) appeared unchanged, the local microstructure was continuously transformed. After 1 turn of HPT, the decomposed UFG structure contained relatively large precipitates inside grains. In the sample processed by five turns in HPT, the segregation of Zn atoms into grain boundaries (GBs) was also observed. After 10 turns, more Zn atoms were segregated into GBs and only smaller-sized precipitates were observed inside grains. The intensive solute segregations into GBs may significantly affect the ductility of the material, leading to its ultralow-temperature superplasticity. Our findings pave the way for achieving advanced microstructural and mechanical properties in nanostructured metals and alloys by engineering their precipitation and segregation by means of applying different HPT regimes.

Atomistic origin of high grain boundary resistance in solid electrolyte lanthanum lithium titanate

Lanthanum lithium titanate is one of the promising electrolytes for solid-state lithium-ion batteries due to its high bulk ionic conductivity up to ∼10−3 S/cm. However, the practical application of this material has been bottlenecked by high grain boundary (GB) resistance, while the underlying mechanism is still under debate. Here we report a comprehensive study with direct evidence to reveal the origin of high GB resistance in La2/3–xLi3xTiO3 (LLTO). Atomic-scale observations via advanced scanning transmission electron microscopy show that the GBs are uniformly subject to subsurface segregation of La atoms to compensate for the excess surface charges. The La segregation leads to an abrupt decrease of charge carrier concentration neighboring GBs and hence is supposed to have deleterious effect on GB conductivity. The findings suggest a novel mechanism of space-charge-induced cation segregation, which shed lights on the intrinsic origin of low GB ionic conductivity in LLTO.