Tunneling Interpenetrative Lithium Ion Conduction Channels in Polymer-in-Ceramic Composite Solid Electrolytes.

Polymer-in-ceramic composite solid electrolytes (PIC-CSEs) provide important advantages over individual organic or inorganic solid electrolytes. In conventional PIC-CSEs, the ion conduction pathway is primarily confined to the ceramics, while the faster routes associated with the ceramic-polymer interface remain blocked. This challenge is associated with two key factors: (i) the difficulty in establishing extensive and uninterrupted ceramic-polymer interfaces due to ceramic aggregation; (ii) the ceramic-polymer interfaces are unresponsive to conducting ions because of their inherent incompatibility. Here, we propose a strategy by introducing polymer-compatible ionic liquids (PCILs) to mediate between ceramics and the polymer matrix. This mediation involves the polar groups of PCILs interacting with Li+ ions on the ceramic surfaces as well as the interactions between the polar components of PCILs and the polymer chains. This strategy addresses the ceramic aggregation issue, resulting in uniform PIC-CSEs. Simultaneously, it activates the ceramic-polymer interfaces by establishing interpenetrating channels that promote the efficient transport of Li+ ions across the ceramic phase, the ceramic-polymer interfaces, and the intervening pathways. Consequently, the obtained PIC-CSEs exhibit high ionic conductivity, exceptional flexibility, and robust mechanical strength. A PIC-CSE comprising poly(vinylidene fluoride) (PVDF) and 60 wt % PCIL-coated Li3Zr2Si2PO12 (LZSP) fillers showcasing an ionic conductivity of 0.83 mS cm-1, a superior Li+ ion transference number of 0.81, and an elongation of ∼300% at 25 °C could be produced on meter-scale. Its lithium metal pouch cells show high energy densities of 424.9 Wh kg-1 (excluding packing films) and puncture safety. This work paves the way for designing PIC-CSEs with commercial viability.

Aluminium ion doping mechanism of lithium thiophosphate based solid electrolytes revealed with solid-state NMR.

We investigate the impact of Al incorporation on the structure and dynamics of Al-doped lithium thiophosphates (Li3-3xAlxPS4) based on ß-Li3PS4. 27Al and 6Li magic-angle spinning NMR spectra confirm that Al3+ ions occupy octahedral sites in the structure. Quantitative analyses of 27Al NMR spectra show that the maximum Al incorporation is x = 0.06 in Li3-3xAlxPS4. The ionic conductivity of ß-Li3PS4 is enhanced by over a factor 3 due to Al incorporation. Further increase of the Al doping level leads to the formation of a more complicated material consisting of multiple crystalline and distorted phases as indicated by 31P NMR spectra and powder X-ray diffraction. Consequently, novel Li ion diffusion pathways develop leading to a very high ionic conductivity at room temperature. NMR relaxometry shows that the activation barrier for long-range Li ion diffusion in ß-Li3PS4 hardly changes upon Al incorporation, but the onset temperature for motional narrowing comes down significantly due to Al doping. The activation barrier in the subsequently formed multiphase material decreases significantly, however, indicating a different more efficient Li ion conduction pathway.

Multicore Liquid Perfluorocarbon-Loaded Multimodal Nanoparticles for Stable Ultrasound and 19F MRI Applied to In Vivo Cell Tracking.

Ultrasound is the most commonly used clinical imaging modality. However, in applications requiring cell-labeling, the large size and short active lifetime of ultrasound contrast agents limit their longitudinal use. Here, 100 nm radius, clinically applicable, polymeric nanoparticles containing a liquid perfluorocarbon, which enhance ultrasound contrast during repeated ultrasound imaging over the course of at least 48 h, are described. The perfluorocarbon enables monitoring the nanoparticles with quantitative 19F magnetic resonance imaging, making these particles effective multimodal imaging agents. Unlike typical core-shell perfluorocarbon-based ultrasound contrast agents, these nanoparticles have an atypical fractal internal structure. The nonvaporizing highly hydrophobic perfluorocarbon forms multiple cores within the polymeric matrix and is, surprisingly, hydrated with water, as determined from small-angle neutron scattering and nuclear magnetic resonance spectroscopy. Finally, the nanoparticles are used to image therapeutic dendritic cells with ultrasound in vivo, as well as with 19F MRI and fluorescence imaging, demonstrating their potential for long-term in vivo multimodal imaging.

Influence of Levulinic Acid Hydrogenation on Aluminum Coordination in Zeolite-Supported Ruthenium Catalysts: A 27 Al 3QMAS Nuclear Magnetic Resonance Study.

The influence of a highly oxygenated, polar protic reaction medium, that is, levulinic acid in 2-ethylhexanoic acid, on the dealumination of two zeolite-supported ruthenium catalysts, namely Ru/H-ß and Ru/H-ZSM-5, has been investigated by 27 Al triple-quantum magic-angle spinning nuclear magnetic resonance spectroscopy (3QMAS NMR). Upon use of these catalysts in the hydrogenation of levulinic acid, the heterogeneity in aluminum speciation is found to increase for both Ru/H-ZSM-5 and Ru/H-ß. For Ru/H-ZSM-5, the symmetric, tetrahedral framework aluminum species (FAL) were found to be mainly converted into distorted tetrahedral FAL species, with limited loss of aluminum to the solution by leaching. A severe loss of both FAL and extra-framework aluminum (EFAL) species into the liquid phase was observed for Ru/H-ß instead. The large decrease in tetrahedral FAL species, in particular, results in a significant decrease in strong acid sites, as corroborated by Fourier transform infrared spectroscopy (FT-IR). This decrease in acidity, evidence of the inferior stability of the strongly acidic sites in Ru/H-ß relative to Ru/H-ZSM-5 under the applied conditions, is considered as the main reason for differences seen in catalyst performance.

The coordinative state of aluminium alkyls in Ziegler-Natta catalysts.

The most commonly used cocatalyst species in Ziegler-Natta catalysts are aluminium alkyls. In this study we aim to find the interaction between aluminium centres of these activators and other components in the ZNC system. Initially we look at binary systems of Al-alkyl/MgCl2 and ternary systems of Al-alkyl/MgCl2/TiCl4, followed by donor containing systems. The aluminium alkyls prove to be very reactive species and only in the case of trimethylaluminium the alkyl is strongly present in the sample. This species appears to convert, however, over time. 1H NMR proves to be an efficient method to detect the presence of the Al-alkyl species. The use of high magnetic field strengths and 27Al MQMAS NMR alleviates signal overlap and gives insight in the dominant line broadening mechanisms thus providing an in-depth view of the cocatalyst. Various Al species with different coordinations can be identified in the samples. The heterogeneity of the samples turns out to have a larger effect on the 27Al NMR spectra than the quadrupolar interaction, which argues against the presence of highly distorted sites with mixed coordinations. Nevertheless for the samples indicating the presence of alkyls in the 1H NMR spectra, we observe an aluminium site at 97 ppm in the 27Al spectra that might be coordinated to an organic group.

Unravelling Li-Ion Transport from Picoseconds to Seconds: Bulk versus Interfaces in an Argyrodite Li6PS5Cl-Li2S All-Solid-State Li-Ion Battery.

One of the main challenges of all-solid-state Li-ion batteries is the restricted power density due to the poor Li-ion transport between the electrodes via the electrolyte. However, to establish what diffusional process is the bottleneck for Li-ion transport requires the ability to distinguish the various processes. The present work investigates the Li-ion diffusion in argyrodite Li6PS5Cl, a promising electrolyte based on its high Li-ion conductivity, using a combination of (7)Li NMR experiments and DFT based molecular dynamics simulations. This allows us to distinguish the local Li-ion mobility from the long-range Li-ion motional process, quantifying both and giving a coherent and consistent picture of the bulk diffusion in Li6PS5Cl. NMR exchange experiments are used to unambiguously characterize Li-ion transport over the solid electrolyte-electrode interface for the electrolyte-electrode combination Li6PS5Cl-Li2S, giving unprecedented and direct quantitative insight into the impact of the interface on Li-ion charge transport in all-solid-state batteries. The limited Li-ion transport over the Li6PS5Cl-Li2S interface, orders of magnitude smaller compared with that in the bulk Li6PS5Cl, appears to be the bottleneck for the performance of the Li6PS5Cl-Li2S battery, quantifying one of the major challenges toward improved performance of all-solid-state batteries.

Effect of Preparation Methods on the Interface of LiBH4/SiO2 Nanocomposite Solid Electrolytes.

Nanocomposites of complex metal hydrides and oxides are promising solid state electrolytes. The interaction of the metal hydride with the oxide results in a highly conducting interface layer. Up until now it has been assumed that the interface chemistry is independent of the nanoconfinement method. Using 29Si solid state NMR and LiBH4/SiO2 as a model system, we show that the silica surface chemistry differs for nanocomposites prepared via melt infiltration or ball milling. After melt infiltration, a Si···H···BH3 complex is present on the interface, together with silanol and siloxane groups. However, after ball milling, the silica surface consists of Si- H sites, and silanol and siloxane groups. We propose that this change is related to a redistribution of silanol groups on the silica surface during ball milling, where free silanol groups are converted to mutually hydrogen-bonded silanol groups. The results presented here help to explain the difference in ionic conductivity between nanocomposites prepared via ball milling and melt infiltration.

On the "tertiary structure" of poly-carbenes; self-assembly of sp3-carbon-based polymers into liquid-crystalline aggregates.

The self-assembly of poly(ethylidene acetate) (st-PEA) into van der Waals-stabilized liquid-crystalline (LC) aggregates is reported. The LC behavior of these materials is unexpected, and unusual for flexible sp(3)-carbon backbone polymers. Although the dense packing of polar ester functionalities along the carbon backbone of st-PEA could perhaps be expected to lead directly to rigid-rod behavior, molecular modeling reveals that individual st-PEA chains are actually highly flexible and should not reveal rigid-rod induced LC behavior. Nonetheless, st-PEA clearly reveals LC behavior, both in solution and in the melt over a broad elevated temperature range. A combined set of experimental measurements, supported by MM/MD studies, suggests that the observed LC behavior is due to self-aggregation of st-PEA into higher-order aggregates. According to MM/MD modeling st-PEA single helices adopt a flexible helical structure with a preferred trans-gauche syn-syn-anti-anti orientation. Unexpectedly, similar modeling experiments suggest that three of these helices can self-assemble into triple-helical aggregates. Higher-order assemblies were not observed in the MM/MD simulations, suggesting that the triple helix is the most stable aggregate configuration. DLS data confirmed the aggregation of st-PEA into higher-order structures, and suggest the formation of rod-like particles. The dimensions derived from these light-scattering experiments correspond with st-PEA triple-helix formation. Langmuir-Blodgett surface pressure-area isotherms also point to the formation of rod-like st-PEA aggregates with similar dimensions as st-PEA triple helixes. Upon increasing the st-PEA concentration, the viscosity of the polymer solution increases strongly, and at concentrations above 20 wt % st-PEA forms an organogel. STM on this gel reveals the formation of helical aggregates on the graphite surface-solution interface with shapes and dimensions matching st-PEA triple helices, in good agreement with the structures proposed by molecular modeling. X-ray diffraction, WAXS, SAXS and solid state NMR spectroscopy studies suggest that st-PEA triple helices are also present in the solid state, up to temperatures well above the melting point of st-PEA. Formation of higher-order aggregates explains the observed LC behavior of st-PEA, emphasizing the importance of the "tertiary structure" of synthetic polymers on their material properties.

Re-investigating the structure-property relationship of the solid electrolytes Li 3-x In1-x Zr x Cl6 and the impact of In-Zr(iv) substitution.

Chloride-based solid electrolytes are considered interesting candidates for catholytes in all-solid-state batteries due to their high electrochemical stability, which allows the use of high-voltage cathodes without protective coatings. Aliovalent Zr(iv) substitution is a widely applicable strategy to increase the ionic conductivity of Li3M(iii)Cl6 solid electrolytes. In this study, we investigate how Zr(iv) substitution affects the structure and ion conduction in Li3-x In1-x Zr x Cl6 (0 ≤ x ≤ 0.5). Rietveld refinement using both X-ray and neutron diffraction is used to make a structural model based on two sets of scattering contrasts. AC-impedance measurements and solid-state NMR relaxometry measurements at multiple Larmor frequencies are used to study the Li-ion dynamics. In this manner the diffusion mechanism and its correlation with the structure are explored and compared to previous studies, advancing the understanding of these complex and difficult to characterize materials. It is found that the diffusion in Li3InCl6 is most likely anisotropic considering the crystal structure and two distinct jump processes found by solid-state NMR. Zr-substitution improves ionic conductivity by tuning the charge carrier concentration, accompanied by small changes in the crystal structure which affect ion transport on short timescales, likely reducing the anisotropy.

Self-organized hetero-nanodomains actuating super Li+ conduction in glass ceramics.

Easy-to-manufacture Li2S-P2S5 glass ceramics are the key to large-scale all-solid-state lithium batteries from an industrial point of view, while their commercialization is greatly hampered by the low room temperature Li+ conductivity, especially due to the lack of solutions. Herein, we propose a nanocrystallization strategy to fabricate super Li+-conductive glass ceramics. Through regulating the nucleation energy, the crystallites within glass ceramics can self-organize into hetero-nanodomains during the solid-state reaction. Cryogenic transmission electron microscope and electron holography directly demonstrate the numerous closely spaced grain boundaries with enriched charge carriers, which actuate superior Li+-conduction as confirmed by variable-temperature solid-state nuclear magnetic resonance. Glass ceramics with a record Li+ conductivity of 13.2 mS cm-1 are prepared. The high Li+ conductivity ensures stable operation of a 220 µm thick LiNi0.6Mn0.2Co0.2O2 composite cathode (8 mAh cm-2), with which the all-solid-state lithium battery reaches a high energy density of 420 Wh kg-1 by cell mass and 834 Wh L-1 by cell volume at room temperature. These findings bring about powerful new degrees of freedom for engineering super ionic conductors.

Refocused continuous-wave decoupling: a new approach to heteronuclear dipolar decoupling in solid-state NMR spectroscopy.

A novel strategy for heteronuclear dipolar decoupling in magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy is presented, which eliminates residual static high-order terms in the effective Hamiltonian originating from interactions between oscillating dipolar and anisotropic shielding tensors. The method, called refocused continuous-wave (rCW) decoupling, is systematically established by interleaving continuous wave decoupling with appropriately inserted rotor-synchronized high-power π refocusing pulses of alternating phases. The effect of the refocusing pulses in eliminating residual effects from dipolar coupling in heteronuclear spin systems is rationalized by effective Hamiltonian calculations to third order. In some variants the π pulse refocusing is supplemented by insertion of rotor-synchronized π/2 purging pulses to further reduce the residual dipolar coupling effects. Five different rCW decoupling sequences are presented and their performance is compared to state-of-the-art decoupling methods. The rCW decoupling sequences benefit from extreme broadbandedness, tolerance towards rf inhomogeneity, and improved potential for decoupling at relatively low average rf field strengths. In numerical simulations, the rCW schemes clearly reveal superior characteristics relative to the best decoupling schemes presented so far, which we to some extent also are capable of demonstrating experimentally. A major advantage of the rCW decoupling methods is that they are easy to set up and optimize experimentally.

The Nature of Interface Interactions Leading to High Ionic Conductivity in LiBH4/SiO2 Nanocomposites.

Complex metal hydride/oxide nanocomposites are a promising class of solid-state electrolytes. They exhibit high ionic conductivities due to an interaction of the metal hydride with the surface of the oxide. The exact nature of this interaction and composition of the hydride/oxide interface is not yet known. Using 1H, 7Li, 11B, and 29Si NMR spectroscopy and lithium borohydride confined in nanoporous silica as a model system, we now elucidate the chemistry and dynamics occurring at the interface between the scaffold and the complex metal hydride. We observed that the structure of the oxide scaffold has a significant effect on the ionic conductivity. A previously unknown silicon site was observed in the nanocomposites and correlated to the LiBH4 at the interface with silica. We provide a model for the origin of this silicon site which reveals that siloxane bonds are broken and highly dynamic silicon-hydride-borohydride and silicon-oxide-lithium bonds are formed at the interface between LiBH4 and silica. Additionally, we discovered a strong correlation between the thickness of the silica pore walls and the fraction of the LiBH4 that displays fast dynamics. Our findings provide insights on the role of the local scaffold structure and the chemistry of the interaction at the interface between complex metal hydrides and oxide hosts. These findings are relevant for other complex hydride/metal oxide systems where interface effects leads to a high ionic conductivity.

Improving Li-ion interfacial transport in hybrid solid electrolytes.

The development of commercial solid-state batteries has to date been hindered by the individual limitations of inorganic and organic solid electrolytes, motivating hybrid concepts. However, the room-temperature conductivity of hybrid solid electrolytes is still insufficient to support the required battery performance. A key challenge is to assess the Li-ion transport over the inorganic and organic interfaces and relate this to surface chemistry. Here we study the interphase structure and the Li-ion transport across the interface of hybrid solid electrolytes using solid-state nuclear magnetic resonance spectroscopy. In a hybrid solid polyethylene oxide polymer-inorganic electrolyte, we introduce two representative types of ionic liquid that have different miscibilities with the polymer. The poorly miscible ionic liquid wets the polymer-inorganic interface and increases the local polarizability. This lowers the diffusional barrier, resulting in an overall room-temperature conductivity of 2.47 × 10-4 S cm-1. A critical current density of 0.25 mA cm-2 versus a Li-metal anode shows improved stability, allowing cycling of a LiFePO4-Li-metal solid-state cell at room temperature with a Coulombic efficiency of 99.9%. Tailoring the local interface environment between the inorganic and organic solid electrolyte components in hybrid solid electrolytes seems to be a viable route towards designing highly conducting hybrid solid electrolytes.

A Water-Free In Situ HF Treatment for Ultrabright InP Quantum Dots.

Indium phosphide quantum dots are the main alternative for toxic and restricted Cd-based quantum dots for lighting and display applications, but in the absence of protecting ZnSe and/or ZnS shells, InP quantum dots suffer from low photoluminescence quantum yields. Traditionally, HF treatments have been used to improve the quantum yield of InP to ∼50%, but these treatments are dangerous and not well understood. Here, we develop a postsynthetic treatment that forms HF in situ from benzoyl fluoride, which can be used to strongly increase the quantum yield of InP core-only quantum dots. This treatment is water-free and can be performed safely. Simultaneous addition of the z-type ligand ZnCl2 increases the photoluminescence quantum yield up to 85%. Structural analysis via XPS as well as solid state and solution NMR measurements shows that the in situ generated HF leads to a surface passivation by indium fluoride z-type ligands and removes polyphosphates, but not PO3 and PO4 species from the InP surface. With DFT calculations it is shown that InP QDs can be trap-free even when PO3 and PO4 species are present on the surface. These results show that both polyphosphate removal and z-type passivation are necessary to obtain high quantum yields in InP core-only quantum dots. They further show that core-only InP QDs can achieve photoluminescence quantum yields rivalling those of InP/ZnSe/ZnS core/shell/shell QDs and the best core-only II-VI QDs.

Equilibrium lithium-ion transport between nanocrystalline lithium-inserted anatase TiO2 and the electrolyte.

The power density of lithium-ion batteries requires the fast transfer of ions between the electrode and electrolyte. The achievable power density is directly related to the spontaneous equilibrium exchange of charged lithium ions across the electrolyte/electrode interface. Direct and unique characterization of this charge-transfer process is very difficult if not impossible, and consequently little is known about the solid/liquid ion transfer in lithium-ion-battery materials. Herein we report the direct observation by solid-state NMR spectroscopy of continuous lithium-ion exchange between the promising nanosized anatase TiO(2) electrode material and the electrolyte. Our results reveal that the energy barrier to charge transfer across the electrode/electrolyte interface is equal to or greater than the barrier to lithium-ion diffusion through the solid anatase matrix. The composition of the electrolyte and in turn the solid/electrolyte interface (SEI) has a significant effect on the electrolyte/electrode lithium-ion exchange; this suggests potential improvements in the power of batteries by optimizing the electrolyte composition.

High-resolution solid-state (13)C µMAS NMR with long coherence life times.

Longer coherence life times (i.e. smaller homogeneous linewidths) can be achieved for carbon resonances which are strongly coupled to protons with high rf field heteronuclear decoupling in micro magic angle spinning NMR. Better proton decoupling enhances the sensitivity and resolution of two-dimensional through-bond correlation experiments for mass-limited samples with uniform carbon labeling.

Hydrogen bonding and chemical shift assignments in carbazole functionalized isocyanides from solid-state NMR and first-principles calculations.

Carbazole functionalized polyisocyanides are known to exhibit excellent electronic properties (E. Schwartz, et al., Chemistry of Materials, 2010, 22, 2597). The functionalities and properties of such materials crucially depend on the organization and stability of the polymer structure. We combine solid-state Nuclear Magnetic Resonance (NMR) experiments with first-principles calculations of isotropic chemical shifts, within the recently developed converse approach, to rationalize the origin of isotropic chemical shifts in the crystalline monomer l-isocyanoalanine 2-(9H-carbazol-9-yl) ethyl amide (monomer 1) and thereby gain insight into the structural organization of its polymer (polymer 2). The use of state-of-the-art solid-state NMR experiments combined with Density Functional Theory (DFT) based calculations allows an unambiguous assignment of all proton and carbon resonances of the monomer. We were able to identify the structure stabilising interactions in the crystal and understand the influence of the molecular packing in the crystal structure on the chemical shift data observed in the NMR spectra. Here the Nuclear Independent Chemical Shift (NICS) approach allows discriminating between 'physical' interactions amongst neighboring molecules such as ring-current effects and 'chemical' interactions such as hydrogen bonding. This analysis reveals that the isocyanide monomer is stabilized by multiple hydrogen bonds such as a bifurcated hydrogen bond involving -N-H, -C-H and O=C- moieties and Ar-H···C≡N- hydrogen bonding (Ar = aromatic group). Based on the geometrical arrangement it is postulated that the carbazole units are involved in the weak σ-π interactions giving rise to a Herringbone packing of the molecules. The chemical shift analysis of the polymer spectra readily establishes the existence of N-H···O=C hydrogen bonds despite the limited resolution exhibited by the polymer spectra. It is also elucidated that the relative arrangement of the carbazole units in the polymer differs significantly from that of the monomer.

Framework and extra-framework aluminium in wet ion exchanged Fe-ZSM5 and the effect of steam during the decomposition of N2O.

The role of extra-framework and framework aluminium in wet-ion exchanged Fe-ZSM5 has been studied using (29)Si NMR and (27)Al triple quantum magic angle spinning (3QMAS) NMR. A series of samples were studied, the parent material, the wet ion exchanged Fe-ZSM5 and Fe-ZSM5 that has been used in the decomposition of N(2)O with varying reaction conditions. Various framework and extra-framework aluminium species have been identified. It was found that cationic Fe species prefer to replace the Brønsted acid protons in their charge balancing role at those aluminium sites associated with the largest quadrupolar product. The framework aluminium atoms that pertain to the smaller quadrupolar product, which are either charge balanced by extra-framework aluminium or a proton, are much less prone to exchange. In the catalytic decomposition of N(2)O it seemed that water present in small amounts enhances the catalytic activity. However, water also decreases the long term stability and performance by dealuminating the zeolite framework. With a high amount of water present, Fe-ZSM5 was destabilised and catalytically inferior.

Full quadrupolar tensor determination by NMR using a micro-crystal spinning at the magic angle.

An implementation of rotor-synchronised Magic Angle Spinning (MAS) NMR is presented to determine the quadrupolar coupling tensor values from a single crystal study for half-integer quadrupolar nuclei. Using a microcoil based probehead for studying micro crystals with superior sensitivity, we successfully determine the full quadrupolar tensor of (23)Na using a micro crystal of dimensions 210 x 210 x 700 mum of NaNO(3) as a model system. A two step simulation procedure is used to obtain the orientation of the quadrupolar tensor information from the experimental spectra and is verified by XRD analysis.

A solid-state NMR and DFT study of compositional modulations in Al(x)Ga(1-x)As.

We have conducted (75)As and (69)Ga Nuclear Magnetic Resonance (NMR) experiments to investigate order/disorder in Al(x)Ga(1-x)As lift-off films with x∼ 0.297 and 0.489. We were able to identify all possible As(Al(n)Ga(4-n)) sites with n = 0-4 coordinations in (75)As NMR spectra using spin-echo experiments at 18.8 Tesla. This was achieved by employing high rf field strengths using a small solenoid coil and an NMR probe specifically designed for this purpose. Spectral deconvolution, using an evolutionary algorithm, complies with the absence of long-range order if a CuAu based order parameter is imposed. An unconstrained fit shows a deviation of the statistics imposed by this type of ordering. The occupational disorder in the Ga and Al positions is reflected in a distribution of the Electric Field Gradients (EFGs) experienced at the different arsenic sites. We established that this can be modelled by summing the effects of the first coordination sphere and a Czjzek type distribution resulting from the compositional variation in the Al/Ga sub-lattice in the higher coordination spheres. (69)Ga 3QMAS and nutation data exclude the presence of highly symmetric sites and also show a distribution in EFG. The experimentally obtained quadrupolar interactions are in good agreement with calculations based on Density Functional Theory (DFT). Using additivity of EFG tensors arising from distant charge perturbations, we could use DFT to model the EFG distributions of the n = 0-4 sites, reproducing the Czjzek and extended Czjzek distributions that were found experimentally. On the basis of these calculations we conclude that the (75)As quadrupolar interaction is sensitive to compositional modulations up to the 7th coordination shell in these systems.