Higher Coordination Number Research Articles

Acoustic Wave Velocities of Ferrous‐Bearing MgSiO3 Glass up to 158 GPa With Implications for Dense Silicate Melts at the Base of the Earth's Mantle

AbstractWe conducted in situ high‐pressure acoustic‐wave velocity measurements of Fe2+‐bearing MgSiO3 glass up to 158 GPa by Brillouin scattering spectroscopy to clarify the effect of iron on the elasticity and structural evolution of silicate melts in the lower mantle. The change in trend of the VS profile, likely induced by the structural transition of Si‐O coordination number from 6 to 6+ proposed in previous studies of silicate glasses, was confirmed to be located at ∼106 GPa. Given the iron contents of partial melts derived from a pyrolitic or chondritic mantle, the transition pressure would be at around 84–97 GPa, which is well within the lowermost‐mantle pressure regime. Our data show the substitution of 12 mol% Fe in MgSiO3 glass decreases the VS by ∼5.5%. This implies that iron affects the buoyancy relations between melts/crystals and the melts at the lowermost mantle will have the higher coordination number than 6.

Incorporating Ytterbium (III) and Bismuth (III) ions into NaInS2 nanocrystals toward enhanced visible absorption and near-infrared emission

Constructing lanthanide doped semiconductor nanocrystals (Ln-SNCs) is a promising strategy for combining of bright, long-lived, and spectrally narrow Ln3+ emission, along with strong broadband absorption and low-phonon-energy crystalline environment of semiconductor to make new spectral-conversion nanophosphors. NaInS2 SNC is one of the most important host series for its high stability and non-toxicity as compared to those widely explored Ln doped perovskite SNCs. Such a family SNCs provide high cation coordination numbers (CN) of 6, which fulfills the cation the fundamental prerequisite for Ln3+ doping. However, the photoluminescence quantum yields (PL QYs) of Yb3+ doped NaInS2 are still below 8% in most SNCs thus far, restricting their further application in near-infrared (NIR) bio-probe. Here, we demonstrate a strategy for accessing Yb3+/Bi3+-codoped NaInS2 SNCs for strong NIR emission. In order to improve the NIR emission, we introduce Bi3+ ions to create new excitation channels, aiming at enhancing the ultra-violet (UV) and visible light absorption. Furthermore, an ZnS outer-layer growth on Ln-doped NaInS2:Bi passivates the surface of SNCs and suppresses the surface defect related non-radiative recombination losses. Our NaInS2:Yb/Bi@ZnS SNCs exhibit efficient NIR emission around 1000 nm with a notable PL QY of 9.5%, suggesting their potential applications in NIR bio-imaging.

Non-covalent Cl⋯X interactions in several silver compounds based on [B12Cl12]2− clusters: 35Cl NQR and X-ray diffraction

Silver cluster compounds Ag2[B12Cl12](1), (Ag(CH3CN)4)2[B12Cl12] (2), and (Ag(CH3CN)2)2[B12Cl12] (3) with very different types of silver environment in crystals were synthesized and investigated using X-ray diffraction analysis (XRD), X-ray phase analysis and nuclear quadrupole resonance (35Cl NQR). Non-covalent interactions of chlorines with surrounding atoms were identified and analyzed using 35Cl NQR spectroscopy. The results were compared with those of XRD to show that the “short” contacts between atomic nuclei do not necessarily indicate the presence of an attraction interaction between the corresponding atoms. Numerous weak interhalogen Cl⋯Cl interactions were revealed in 1, while the Ag⋯Cl ineractions seem to be weakened due to high coordination number of silver atom. In 2, no Ag⋯Cl interactions were detected by X-ray diffraction, while non-covalent Cl⋯C, Cl⋯H and Cl⋯Cl interactions were found. As the NQR spectra indicated, interhalogen interactions in 2 appeared to be the strongest of all the others. In 3, interhalogen Cl⋯Cl interactions were the weakest, the largest contribution to the electric field gradient on the Cl atoms being made by silver atoms.

CRYSTAL STRUCTURE OF THE TmNi5

Сrystal structure of the TmNi5 compound has been investigated by means of X-ray single crystal method (Oxford Diffraction X’calibur four-circle diffractometer, MoKα radiation) for the first time: CaCu5-type structure, Pearson symbol hP6, space group P6/mmm, a = 4.8684(12), c = 3.9541(7) Å, R1 = 0.0529, wR2 = 0.1835 for 80 reflections. Similarly to intermetallic compounds with high transition metal content, atoms in the title structure have rather high coordination numbers: 20 for thulium and 12 for nickel.

Boron Nitride- and Graphene-Supported Trimetallic Yolk–Shell and Hollow Nanoparticles

In this study, the stability of yolk–shell and hollow Ni@PdAu and PdAu@Ni nanoparticles in free state and supported on boron nitride and graphene substrates was investigated at 300 K using molecular dynamics simulations. To this end, analyses of several parameters such as relative stability, surface energy, coordination number, number of surface atoms, bond length, displacement vector, and atomic strain were employed. Results show that the yolk–shell and hollow Ni@PdAu nanoparticles are more stable than yolk–shell and hollow PdAu@Ni nanoparticles in free and supported states due to the less surface energy. Furthermore, results show that the hollow nanoparticles are more stable than yolk–shell nanoparticles in all states. In addition, results show that the void and hollow core in yolk–shell and hollow nanoparticles are unstable and collapse due to the contraction and expansion of the core and shell, which lead to the formation of the core–shell and quasi–Janus structures in hollow and yolk–shell nanoparticles, respectively. Moreover, nanoparticles create a quasi–ellipsoid structure with low density and high coordination number on the boron nitride. The yolk–shell and hollow nanoparticles are the most stable on the boron nitride due to the smaller displacement and variation of the atomic bond length and lower atomic strain, which are caused by the strong nonbonded interaction, good atomic match, and placement of the Ni, Au, and Pd atoms on the middle position of the boron nitride hexagonal structure. Generally, this study demonstrated that the stability of yolk–shell and hollow nanoparticles can be tuned by the substrate–nanoparticle interaction.

Switchable Nonlinear Optical Absorption of Metal–Organic Frameworks

AbstractMetal–organic frameworks (MOFs) are widely explored owing to their excellent nonlinear optical (NLO) properties. However, researchers have mainly focused on designing new structures of MOF crystals to adjust the NLO response while ignoring the influence of the number of metal–ligand coordination bonds on the NLO properties of MOFs. In this study, the influence of the coordination numbers of MOFs on their NLO properties is studied for the first time. Herein, MOFs with different coordination numbers, using trifluoroacetic acid as an auxiliary agent, are synthesized and their NLO properties are tested using the Z‐scan technique. The results reveal that the NLO absorption properties of MOFs with high coordination numbers can be effectively modulated from saturable absorption to reverse saturable absorption by increasing the excitation intensity. First‐principles calculations show that a change in the coordination numbers leads to a change in the charge transfer from metal to ligand, thereby resulting in different NLO responses. The MOFs with a high coordination number have potential applications in novel optical switches or logic gates. These results provide a reference for the precise adjustment of the NLO properties of MOFs.

Theoretical Prediction and Experimental Validation of the Glass-Forming Ability and Magnetic Properties of Fe-Si-B Metallic Glasses from Atomic Structures.

Developing new soft magnetic amorphous alloys with a low cost and high saturation magnetization (Bs) in a simple alloy system has attracted substantial attention for industrialization and commercialization. Herein, the glass-forming ability (GFA), thermodynamic properties, soft magnetic properties, and atomic structures of Fe80+xSi5−xB15 (x = 0–4) amorphous soft magnetic alloys were investigated by ab initio molecular dynamics (AIMD) simulations and experiments. The pair distribution function (PDF), Voronoi polyhedron (VP), coordination number (CN), and chemical short- range order (CSRO) were analyzed based on the AIMD simulations for elucidating the correlations between the atomic structures with the glass-forming ability and magnetic properties. For the studied compositions, the Fe82Si3B15 amorphous alloy was found to exhibit the strongest solute–solute avoidance effect, the longest Fe-Fe bond, a relatively high partial CN for the Fe-Fe pair, and the most pronounced tendency to form more stable clusters. The simulation results indicated that Fe82Si3B15 was the optimum composition balancing the saturation magnetization and the GFA. This prediction was confirmed by experimental observations. The presented work provides a reference for synthesizing new Fe-Si-B magnetic amorphous alloys.

(C5H6N)Pb2X5 (X = Cl, Br): Hybrid Lead Halides Based on Seven-Coordinate Pb(II)

Hybrid lead halides are a diverse family of compounds, of interest for their optoelectronic properties, that vary in the dimensionality and connectivity of their inorganic substructures. The great majority of these compounds are based on lead-centered octahedra, with few examples featuring inorganic architectures containing higher coordination numbers. Here, we report the synthesis and characterization of a pyridinium lead bromide phase that is based on seven-coordinate Pb(II) centers. Through edge- and face-sharing, the polyhedra form a corrugated, two-dimensional inorganic substructure. Electronic structure calculations were used to examine the band structure and the role of the stereoactive lone pair in the inherently asymmetric, seven-coordinate Pb(II) geometry. For reference, we have visualized the role of the lone pair in the binary halide PbBr2, which also has a seven-coordinate inner ligand sphere. A comparison of the new structure with the limited number of existing hybrid lead halides with similar inorganic architectures highlights the templating role of the organic cation for these compounds. We also contribute characterization and discussion of isomorphic pyridinium lead chloride, which had been deposited in the Cambridge Structural Database but never, to our knowledge, addressed in the literature. The compounds were synthesized using solution conditions and structures determined with single-crystal X-ray diffraction. The materials were also characterized via powder X-ray diffraction, combustion elemental analysis, and diffuse reflectance UV-vis spectroscopy. While the structures reported here are centrosymmetric, the seven-coordinate, capped trigonal prismatic geometry that we have identified is a source of local asymmetry that could be used as a component in designing globally noncentrosymmetric structures.

Multiscale morphological and topological characterization of coal microstructure: Insights into the intrinsic structural difference between original and tectonic coals

Multiscale microstructure evolution of tectonic coal determines CBM storage, development and transport mechanism as well as its effect on coal and gas outburst potential. The multi-scale morphological and topological microstructure characterization of original and tectonic coals were performed via the photoelectric & radiation techniques, fluid penetration method and digital core technique, from nanometer scale to micrometer scale. This study concludes that compared to original coals, tectonism coals have enhanced sorption ability with short equilibrium time and lower structural strength basically. With the increase of metamorphism, the surface morphological features could transform from irregular to regular as the banded pore-fractures evolve into uniformly distributed pores; brittle and ductile deformations increase microstructure connectivity and promote more irregular bending coal body than original coals. Metamorphism could accelerate an evolutionary trend from larger pores to smaller pores whereas mesopore and macropore are more sensitive to tectonism than micropore; meanwhile, micropore volume and surface area in high-ranked coals are significantly influenced with the tectonism than middle-ranked coals; besides, the negligible variation in micropores volume serves as a significant contributor to a rapid rise in surface area. Tectonism restrains the increase of effective migration pathways, i.e., the constricted configuration. Physisorption isotherms indirectly verify the coal has diverse pore shapes, such as cylindrical, conical, slit and constricted pores, etc. 3D visualization of tectonic coal morphologically exhibits more microcracks and sporadically distributed pore-connected groups, completely transforming original coal matrix into smaller blocks that promote gas sorption, diffusion and seepage capacity. In this case, the equivalent topological parameters of tectonic coals are strengthened with more developed space-throat properties and higher coordination number. Through the morphological and topological analyses, tectonic coals are identified as the interconnected microstructure with lower pore-throat ratio and tortuosity than original coals, generating more diversified and accessible migration pathway. In light of the aforementioned results, a conceptual schematic presentation was summarized to illustrate the intrinsic structural difference between original and tectonic coals, which are of great guiding significance to the occurrence mechanism of outburst prediction and risk.

Proton Conductive Lanthanide-Based Metal-Organic Frameworks: Synthesis Strategies, Structural Features, and Recent Progress.

In the fields of proton exchange membrane fuel cells as well as impedance recognition, molecular sieve, and biochemistry, the development of proton conductive materials is essential. The design and preparation of the next generation of proton conductive materials-crystalline metal-organic framework (MOF) materials with high proton conductivity and excellent water stability-are facing great challenges. Due to the large radius and high positive charge of lanthanides, they often interact with organic ligands to exhibit high coordination numbers and flexible coordination configurations, resulting in the higher stability of lanthanide-based MOFs (Ln-MOFs) than their transition metal analogues, especially regarding water stability. Therefore, Ln-MOFs have attracted considerable attention. This review offers a view of the latest progress of proton conductive Ln-MOFs, including synthesis strategy, structural characteristics, and advantages, proton conductivity, proton conductive mechanism, and applications. More importantly, by discussing structure-property relationships, we searched for and analyzed design techniques and directions of development of Ln-MOFs in the future. The latest progress of synthesis strategy, structural characteristics, proton conductive properties and mechanism and applications on Ln-MOFs. Ln-MOFS Lanthanide-based MOFs, MOF metal-organic framework, PEMFC proton exchange membrane fuel cells.

Morphologically Flex Sm-MOF Based Electrochemical Immunosensor for Ultrasensitive Detection of a Colon Cancer Biomarker.

Despite having the potential to synthesize stable metal-organic frameworks (MOFs), rare earth metal-based MOFs have not been exploited extensively. Owing to the high coordination numbers, the MOFs can generate a suitable coordination environment for various applications. Herein, samarium (Sm)-based MOFs were synthesized with three different organic linkers, namely, trimesic acid (TMA), meso-tetra(4-carboxyphenyl)porphine (TCPP), and 1,3,6,8-tetra(4-carboxylphenyl) pyrene(TBPy) by the solvothermal approach. The morphologies of Sm-TMA MOF, Sm-TCPP MOF, Sm-TBPy MOF were rod-shaped, cubic consisting of stacked 2D layers, and spherical made of small cubic structures, respectively. After the electrochemical properties of the synthesized MOFs were investigated, the MOFs were used to fabricate immunosensors for detection of carcinoembryonic antigen using a label-free signaling strategy. The immunosensors exhibited a wide linear detection range and a lower detection limit. The exhibited reproducibility and selectivity of the immunosensors were within the tolerable limits. The established label-free immunosensor has been successfully applied for detection of carcinoembryonic antigen in human serum samples, demonstrating that the rare earth metal-based MOFs are promising for construction of biosensors for medical diagnosis.

Crystal structure determination of a new LaPO4 phase in a multicomponent glass ceramic via 3D electron diffraction

A glass ceramic from the MgO–Al 2 O 3 –SiO 2 system containing additives of ZrO 2 , TiO 2 , La 2 O 3 and P 2 O 5 was investigated. Via x-ray powder diffraction (XRPD) and Transmission electron microscopy(TEM) the crystalline phases present could be identified as MgAl 2 O 4 (Spinel), orthorhombic ZrTiO 4 and a polymorph of LaPO 4 with a previously unknown crystal structure. The crystal structure of this LaPO 4 phase was solved ab initio via 3D ED Data. The polymorph occurs in a distorted barite structure type in the same space group (P2 1 /n) as the stable monazite type polymorph, however the density is higher and the La has a higher coordination number. Furthermore the LaPO 4 is present in a spinodal relict microstructure. Potential explanations for the presence of this metastable polymorph are pressure due to residual stresses from the crystallization or surface effects due to the high surface area resulting from the spinodal relict structure.

Effect of Particle Size and Constraint Conditions on Single Particle Strength of Carbonate Sand.

Carbonate sand is often encountered and utilized as construction material in offshore engineering projects. Carbonate sand particles, which are porous and angular, are found to be highly crushable under high stress conditions, whereas the mechanisms and controlling factors for the crushing of carbonate sand particles are not well developed. The crushability and particle strength of around 400 particles from three fractions (5–10 mm, 2–5 mm, and 1–2 mm) of carbonate sand from the South China Sea were investigated via grain-scale single particle crushing tests. Special emphasis was placed on the effect of external constraint conditions (i.e., coordination number) and intrinsic particle morphology characteristics on the particle strength of carbonate soil. The particle strength of carbonate sand was found to be around half of quartz sand in terms of characteristic stress. Negative correlations, which could be depicted by an exponential equation, were found between the particle size and particle strength. Due to elongated particle shape and tensile stress concentration, a higher coordination number may lower the particle strength, which contradicts what was reported for quartz sands. A series of seven fundamental particle dimensions and five particle shape descriptors was characterized, and the aspect ratio was found to be one of the more influential shape descriptors for particle strength. The results enriched the database for the analysis of highly irregular geomaterial and provided insights into controlling factors of particle strength and crushing mechanisms of the carbonate sand.

3D visualization of tectonic coal microstructure and quantitative characterization on topological connectivity of pore-fracture networks by Micro-CT

Research on the connectivity characteristics and topological relationships of pore-fracture networks is crucially significant for systematic understanding the microstructure evolution on original and tectonic coals. From the aspects of digitization, visualization, non-destruction, topologization and quantitation, Micro-CT is adopted to characterize the microstructure of original, tectonic and reconstructed coals. The results indicate that the roughly vertical distribution among cleat system in original coal microstructure regularly splits coal matrix into several cubic blocks. Tectonism induces the fundamental transformation on microstructure, associated with well-developed micro-fractures and sporadic pores distributed in spatial scale. With external stress loading, the internal micro-fractures of reconstructed coal sharply decline and gradually evolves into widely-distributed pore connectivity with locally disorderly and dispersed micro-fractures. Following morphological thinning algorithm, skeletonization models were created to demonstrate that the mean tortuosity of original coal has the highest value of 1.2213, followed by reconstructed and tectonic coals of 1.1741 and 1.1205, respectively. Based on skeletonization, the topological “ball-rod” model and its quantitative connectivity parameters reveal that the equivalent structure of pore space for tectonic coal significantly increases, compared to original coal; however, the reconstructed coal after stress loading decreases slightly to 37.75%. Tectonism may facilitate coal microstructure to generate a high coordination number >10, enhancing the connectivity of tectonic coal; nevertheless, the coordination number of reconstructed coal dropped dramatically due to stress loading. Based on the mentioned above, the pore-scale flow simulation of micro-topological equivalent PNMs was conducted for discovering that pressure distributions of tectonic coal in different directions are more concentrated and uniform than original coal while the latter has a non-uniform flow pattern due to its structural anisotropy and heterogeneity. The aforementioned results have guiding significance for revealing the micro-topological connectivity of pore-fracture network in coal, as well as the pore-scale fluid transporting visualization. • 3D visualization models of coal microstructure were non-destructively established. • 3D skeletonization and PNM were created based on morphological simplification. • Pore-scale flow simulation was conducted by micro-topological equivalent PNMs.

Unusual Intramolecular Motion of ReH92- in K2ReH9 Crystal: Circle Dance and Three-Arm Turnstile Mechanisms Revealed by Computational Studies.

The nonahydridorhenate dianion ReH92- is a unique rhenium polyhydride complex due to its remarkably high coordination number; however, its detailed polytopal rearrangement process in either solution or crystal is so far unclear. In this work, our quantum chemical calculations have identified two previously unreported fluxional mechanisms for the ReH92- dianion in the K2ReH9 crystal: three-arm turnstile rotation and circle dance mechanism. These two polytopal rearrangements in the crystal offer an alternative interpretation to the pulse and wide-line NMR spectra (Farrar et al. J. Chem. Phys. 1969, 51, 3595). The previously postulated hindered rotation of the whole ReH92- dianion in K2ReH9 (White et al. J. Chem. Soc., Faraday Trans. 2 1972, 68, 1414) turns out to be a combination of the above-mentioned two elementary fluxional processes. In addition, our calculations have confirmed the Muetterties' D3h⇌C4v rearrangement as the intramolecular motion for the ReH92- dianion in solution.

DEM investigation on strain localization in a dense periodic granular assembly with high coordination number

Strain localization is one of key phenomena which have been studied extensively in geomaterials and for different kinds of materials including metals and polymers. This well-known phenomenon appears when structure/material is closed to failure. Theoretical, experimental, and numerical research have been dedicated to this subject for a long while. In the numerical aspects, strain localization inside the periodic granular assembly has not been well studied in the literature. In this paper, we investigate the occurrence and development of strain localization within a dense cohesive-frictional granular assembly with high coordination number under bi-periodic boundary conditions by Discrete Element Modeling (DEM). The granular assembly is composed of 2D circular disks and subjected to biaxial loading with constant lateral pressure. The results show that the formation of shear bands is of periodic type, consistent with the boundary conditions. This formation has the origins of the irreversible losing of cohesive contacts, viewed as micro-crackings which strongly concentrated in the periodic shear zones. This micromechanical feature is therefore strongly related to the strain localization observed at the sample scale. Finally, we also show that the strain localization is in perfect agreement with the sample’s displacement fluctuation fields.

Shape stability and electronic structure of Pt3M (M = Co or Ni) alloy nanoparticles

We studied the shape stability of Pt3M alloy nanoparticles (NPs) using density functional theory calculations, where M is Co or Ni. The relationship between the shape and durability of Pt3M NPs is reported. We evaluated the cohesive energies of face-centered cubic (fcc) and face-centered tetragonal (fct) NPs. Truncated octahedron, icosahedron, and truncated cube were considered as shapes for the fcc NPs. The cohesive energies in the truncated octahedral fcc Pt NPs were lower than other shapes, while the icosahedral fcc and truncated octahedral fct Pt3M NPs with the Pt-skin configuration were stable. Co and Ni had lower twin boundary energies than Pt, thus affecting the stability of the icosahedral fcc Pt3M NP; another factor influencing the stability was the high coordination number. An increase in Pt–M bond fraction lowered the cohesive energy of truncated octahedral fct Pt3M NPs. The expansion of the icosahedral fcc NPs competed with the shrinking effect of alloying, thus affecting the d-band center in icosahedral fcc Pt3M NPs. Due to the suppression of the charge transfer and shrinkage effect by alloying, d-band center in the facet with coordination number = 9 was adjusted to the suitable range based on the volcano plot.

Particle flocculation in a stirred tank: A microscopic test by coupled CFD-DEM approach

Particle flocculation in a stirred tank was numerically investigated by a coupled CFD-DEM approach, in which a microscopic test in a typical zone was first proposed instead of solving the full-scale particle field. The flocculation kinetics was described by the Johnson-Kendall-Roberts (JKR) theory, followed by calibration of surface energy parameter. A Volume of Fluid (VOF) model was employed to capture the interface between liquid and air. The two-way coupling of fluid and particle was achieved by resolving pressure gradient force and Gidaspow’s drag force in the momentum equations. Based upon the qualitative and quantitative validation tests in air-water interface pattern and fluid tangential velocity, respectively, the particle coordination number and flocs fractal properties (e.g. fractal dimension, voidage, effective density) were investigated considering the effect of impeller speed. Results show that the number of particles first increases with particle coordination number and then decreases, and is further positively correlated with the stirring intensity in lower coordination numbers (0−3) while negatively correlated in higher coordination numbers (≥5). The influences of turbulence dissipation rate on the average particle coordination number were also investigated in radial, tangential, and axial directions. The mean floc size decreases with impeller speed, however, the fractal dimension increases in a certain range. The voidage increases with the daughter-particle number in a floc while the effective density of flocs is inversely proportional to the floc size. It is recommended to adopt operations that facilitate the one-by-one attachment mode and syneresis for forming relatively large and compact flocs.

Metallization and Superconductivity in the van der Waals Compound CuP2Se through Pressure-Tuning of the Interlayer Coupling.

Emergent layered Cu-bearing van der Waals (vdW) compounds have great potentials for use in electrocatalysis, lithium batteries, and electronic and optoelectronic devices. However, many of their alluring properties such as potential superconductivity remain unknown. In this work, using CuP2Se as a model compound, we explored its electrical transport and structural evolution at pressures up to ∼60 GPa using both experimental determinations and ab initio calculations. We found that CuP2Se undergoes a semiconductor-to-metal transition at ∼20 GPa at room temperature and a metal-to-superconductor transition at 3.3-5.7 K in the pressure range from 27.0 to 61.4 GPa. At ∼10 and 20 GPa, there are two isostructural changes in the compound, corresponding to, respectively, the emergence of the interlayer coupling and start of interlayer atomic bonding. At a pressure between 35 and 40 GPa, the vdW layers start to slide and then merge, forming a new phase with high coordination numbers. We also found that the Bardeen-Cooper-Schrieffer (BCS) theory describes quite well the pressure dependence of the critical temperature despite occurrence of a possible medium-to-strong electron-phonon coupling, revealing the determinant roles of the enhanced bulk modulus and electron density of states at high pressure. Moreover, nanosizing of CuP2Se at high pressure further increased the critical temperature even at sizes approaching the Anderson limit. These findings would have important implications for developing novel applications of layered vdW compounds through simple pressure tuning of the interlayer coupling.

Grain boundary kinetics in magnesium alloys from first principles

Grain boundary migration in magnesium alloys has been studied using quantum mechanical calculations implementing the nudged elastic band method. Four crystallographically different boundaries were examined: two twin boundaries and two general grain boundaries that showed no crystallographic symmetry across the boundary plane. The activation energies for boundary migration were determined from the minimum energy pathways, and these energies were consistent with experimental values. It was found that the activation energy is linearly related to the coordination number of the boundaries. This indicates that boundaries with lower coordination numbers showed smaller activation energies and thus higher mobilities than the more orderly boundaries with larger coordination number and larger activation energies. The effect of solutes at the boundary was also studied, and it was found that most solutes with low co-ordination number decreased the activation energy for boundary migration, but the effect of solutes on boundaries with high coordination number was strongly dependent on the solute chemistry.