Nuclear Magnetic Resonance Spin-lattice Relaxation Research Articles

Li-Ion Dynamics in Li2S:LiI Composites – on the Effect of Solid-Solution Formation on Overall Li+ Transport

The enormous interest in developing powerful all-solid-state Li-ion batteries led to a boost in electrolyte research. Some Li-ion conductors have Ag-bearing analogs; the fast Ag+ ion conductor, Ag3SI, could be one of such materials. So far, no clear evidence is available that the Li-counterpart, Li3SI, does exist. Here, we treated an equimolar mixture of Li2S and LiI in high-energy ball mills and followed structural changes via X-ray diffraction (XRD) and magic-angle spinning (MAS) 6,7Li nuclear magnetic resonance (NMR) measurements. Differences in local structures as sensed by MAS NMR will be discussed for annealed and non-annealed samples, that is, powder samples directly obtained after finishing the ball-milling procedure. For nanocrystalline, non-annealed Li2S:LiI, the MAS NMR response is characterized by a broad distribution of NMR lines showing chemical shifts between that of pure Li2S and LiI, hence pointing to the formation of solid-solution like regions.Ion dynamics on different length scales was probed with variable-temperature, potentiostatic conductivity spectroscopy as well as solid-state NMR spin-lattice relaxation (SLR) measurements. Defect-rich nanocrystalline Li2S:LiI has to be characterized by an overall conductivity that is 2 orders of magnitude higher as compared to that of the microcrystalline, annealed reference sample. SLR NMR experiments supports this result and reveal lower activation energies for both the fast local hopping ion dynamics and long-range ion diffusivity in the sample directly obtained after ball milling. Finally, mixing-time dependent 6Li 2D exchange NMR spectroscopy reveals even (very) slow Li+ exchange between the Li2S-rich and LiI-rich regions in the nanocrystalline sample. Off-diagonal intensities are especially seen for mixing times longer than 80 ms.

The novel oxy-sulfide glassy ionic conductors Na4P2S7-xOx 0 ≤ x ≤ 7: Understanding the features of static and dynamic cations

We present a 23Na nuclear spin dynamics model for interpreting nuclear magnetic resonance (NMR) spin-lattice relaxation and central linewidth data in the invert glass system Na4P2S7-xOx, 0 ≤ x ≤ 7. The glassy nature of this material results in variations in local Na+ cation environments that may be described by a Gaussian distribution of activation energies. A consistent difference between the mean activation energies determined by NMR and DC conductivity measurements was observed, and interpreted using a percolation theory model. From this, the NaNa coordination number in the sodium cation sublattice was obtained. These values were consistent with jumps through tetrahedral faces of the sodium cages for the sulfur rich glasses, x < 5, consistent with proposed models of their short range order (SRO) structures. From NMR spin-echo measurements, we determined the NaNa second moment M2 resulting from the NaNa magnetic dipole interaction of nearest neighbors. Values of M2 obtained as a function of sodium number density N were in agreement with models for uniform sodium distribution, indicating that these invert glass systems form so as to maximize the average NaNa distance. A simple Coulombic attraction model between Na+ cation and X (=S−, O−) anion was applied to calculate the activation energy. In the range 1.5 ≤ x ≤ 7, an increase in activation energy with increasing oxygen content x occurred, and was consistent with the decrease in average anionic radius, and the increase in Coulombic attraction. For small oxygen additions, 0 ≤ x ≤ 1.5, the suggested minimum at low oxygen concentration seen in the activation energies obtained from DC conductivity data is not evident in the model.

Nuclear spin relaxation in aqueous paramagnetic ion solutions.

A Brownian shell model describing the random rotational motion of a spherical shell of uniform particle density is presented and validated by molecular dynamics simulations. The model is applied to proton spin rotation in aqueous paramagnetic ion complexes to yield an expression for the Larmor-frequency-dependent nuclear magnetic resonance spin-lattice relaxation rate T_{1}^{-1}(ω) describing the dipolar coupling of the nuclear spin of the proton with the electronic spin of the ion. The Brownian shell model provides a significant enhancement to existing particle-particle dipolar models without added complexity, allowing fits to experimental T_{1}^{-1}(ω) dispersion curves without arbitrary scaling parameters. The model is successfully applied to measurements of T_{1}^{-1}(ω) from aqueous manganese(II), iron(III), and copper(II) systems where the scalar coupling contribution is known to be small. Appropriate combinations of Brownian shell and translational diffusion models, representing the inner and outer sphere relaxation contributions, respectively, are shown to provide excellent fits. Quantitative fits are obtained to the full dispersion curve of each aquoion with just five fit parameters, with the distance and time parameters each taking a physically justifiable numerical value.

Structural geometry and molecular dynamics of hybrid organic–inorganic [NH3(CH2)6NH3]CdCl4 crystals close to phase transition temperatures

Organic–inorganic hybrid perovskites are highly promising for application in various electrochemical devices, such as batteries and fuel cells. The physical properties of crystals of the organic–inorganic hybrid perovskite [NH3(CH2)6NH3]CdCl4 are important for their future application. Therefore, these crystals were grown and their phase transition temperatures TC1 = 337 K and TC2 = 472 K were determined using powder X-ray diffraction and differential scanning calorimetry. We observed that the crystallographic surroundings of 1H and 13C in the cation near TC1 did not show significant changes, whereas those of 113Cd in the anion changed significantly. The change in the coordination geometry of C1 around Cd near TC1 changed the N–H···Cl bond by connecting with the 1H of NH3. The nuclear magnetic resonance spin-lattice relaxation time T1ρ suggested that the 1H energy transfer processes in phases III and II were easier, whereas the 13C energy transfer processes were easier in phase III than in phase II. The results of the current study for [NH3(CH2)nNH3]CdCl4 (n = 6) were compared with those for n = 2, 3, 4, and 5 obtained from previous studies. The features of the length of CH2 and even–odd number of carbons in the diammonium chain are expected to facilitate potential applications in the future.

Deformed spin- 12 square lattice in antiferromagnetic NaZnVOPO4(HPO4)

We report the structural and magnetic properties of a new spin-$\frac12$ antiferromagnet NaZnVOPO$_4$(HPO$_4$) studied via x-ray diffraction, magnetic susceptibility, high-field magnetization, specific heat, and $^{31}$P nuclear magnetic resonance (NMR) measurements, as well as density-functional band-structure calculations. While thermodynamic properties of this compound are well described by the $J_1-J_2$ square-lattice model, \textit{ab initio} calculations suggest a significant deformation of the spin lattice. From fits to the magnetic susceptibility we determine the averaged nearest-neighbor and second-neighbor exchange couplings of $\bar J_1\simeq -1.3$ K and $\bar J_2\simeq 5.6$ K, respectively. Experimental saturation field of 15.3\,T is consistent with these estimates if 20\% spatial anisotropy in $J_1$ is taken into account. Specific heat data signal the onset of a magnetic long-range order at $T_{\rm N} \simeq 2.1$ K, which is further supported by a sharp peak in the NMR spin-lattice relaxation rate. The NMR spectra mark the superposition of two P lines due to two noneqivalent P sites where the broad line with the strong hyperfine coupling and short $T_1$ is identified as the P(1) site located within the magnetic planes, while the narrow line with the weak hyperfine coupling and long $T_1$ is designated as the P(2) site located between the planes.

Relative Cation-Anion Diffusion in Alkyltriethylammonium-Based Ionic Liquids.

19F Nuclear Magnetic Resonance spin-lattice relaxation experiments have been performed for a series of ionic liquids including the same anion, bis(trifluoromethanesulfonyl)imide, and cations with alkyl chains of different lengths: triethylhexylammonium, triethyloctylammonium, decyltriethylammonium, dodecyltriethylammonium, decyltriethylammonium, and hexadecyltriethylammonium. The experiments have been carried out in a frequency range of 10 kHz to 10 MHz versus temperature. A thorough analysis of the relaxation data has led to the determination of the cation–anion as a relative translation diffusion coefficient. The diffusion coefficients have been compared with the corresponding cation–cation and anion–anion diffusion coefficients, revealing a correlation in the relative translation movement of the anion and the triethylhexylammonium, triethyloctylammonium, decyltriethylammonium, and dodecyltriethylammonium cations, whereas the relative translation diffusion between the anion and the cations with the longer alkyl chains, decyltriethylammonium and hexadecyltriethylammonium, remains rather uncorrelated (correlated to a much lesser extent).

Molecular motion of imidazolium cations and phase transitions in (ImH)2KCo(CN)6 with double perovskite structure

Temperature dependence of 1H nuclear magnetic resonance spin–lattice relaxation time T1 of (ImH)2KCo(CN)6, ImH+: imidazolium cation, is reported. The asymmetric T1 minimum observed in intermediate-temperature phase between 198 and 112 K is analyzed assuming the Cole-Davidson distribution of correlation time. Temperature dependences of 14N nuclear quadrupole resonance frequencies and spin–lattice relaxation times are also reported. The phase transitions at 198 and 112 K are shown to be of second and first order, respectively. The 14N relaxation is shown to be governed by the electric field gradient fluctuation due to the in-plane reorientational motion of the imidazolium cations.

Breakdown of atomic spin-orbit coupling picture in an apparently isolated pseudo-one-dimensional iridate: Sr3NaIrO6

In the presence of strong atomic spin-orbit coupling (SOC), tending to the $j\text{\ensuremath{-}}j$ coupling limit, $5{d}^{4}$ iridates are speculated to possess a nonmagnetic ${J}_{\mathrm{eff}}=0$ singlet ground state from atomic consideration, which invariably gets masked due to different solid-state effects (e.g., hopping). Here, we try to probe the trueness of the atomic SOC-based proposal in an apparently one-dimensional system, ${\mathrm{Sr}}_{3}{\mathrm{NaIrO}}_{6}$, with well-separated ${\mathrm{Ir}}^{5+}$ $(5{d}^{4})$ ions. But all the detailed experimental as well as theoretical characterizations reveal that the ground state of ${\mathrm{Sr}}_{3}{\mathrm{NaIrO}}_{6}$ is not nonmagnetic. However, our combined dc susceptibility $\ensuremath{\chi}$, $^{23}\mathrm{Na}$ nuclear magnetic resonance (NMR), muon spin relaxation/rotation $(\ensuremath{\mu}\mathrm{SR})$, and heat capacity ${C}_{p}$ measurements clearly refute any sign of spin freezing or ordered magnetism among the ${\mathrm{Ir}}^{5+}$ moments due to geometrical exchange frustration, while in-depth zero-field and longitudinal field $\ensuremath{\mu}\mathrm{SR}$ investigations strongly point towards an inhomogeneous quantum spin liquid (QSL)-like ground state. In addition, the linear temperature dependence of both the NMR spin-lattice relaxation rate and the magnetic heat capacity at low temperatures suggest low-lying gapless spin excitations in the QSL phase of this material. Finally, we conclude that the effective SOC realized in ${d}^{4}$ iridates is unlikely to offer a ground state which will be consistent with a purely atomic $j\text{\ensuremath{-}}j$ coupling description.

2H NMR study on temperature-dependent water dynamics in amino-acid functionalized silica nanopores.

We prepare various amino-acid functionalized silica pores with diameters of ∼6 nm and study the temperature-dependent reorientation dynamics of water in these confinements. Specifically, we link basic Lys, neutral Ala, and acidic Glu to the inner surfaces and combine 2H nuclear magnetic resonance spin-lattice relaxation and line shape analyses to disentangle the rotational motions of the surfaces groups and the crystalline and liquid water fractions coexisting below partial freezing. Unlike the crystalline phase, the liquid phase shows reorientation dynamics, which strongly depends on the chemistry of the inner surfaces. The water reorientation is slowest for the Lys functionalization, followed by Ala and Glu and, finally, the native silica pores. In total, the rotational correlation times of water at the different surfaces vary by about two orders of magnitude, where this span is largely independent of the temperature in the range ∼200-250 K.

Transport studies of NaPF6 carbonate solvents-based sodium ion electrolytes

Characterizing fundamental ion transport is necessary for the modification and development of electrolytes. In this study, we investigated the local and bulk transport properties of 1 M NaPF6 in the binary EC:PC (1:1), and ternary 5EC:3PC:2DEC (5:3:2) solvents, as well as their 2 wt.% FEC modulated versions. We determined 1H, 19F and 23Na Nuclear Magnetic Resonance (NMR) spin-lattice relaxation time (T1), self-diffusion coefficient (D), linewidth and chemical shift. These were complimented with density, viscosity and ionic conductivity measurements, all as a function of temperature. Both the viscosity and ionic conductivity displayed VFT behavior and their Walden products showed a dependence on temperature. This coupled with their having the lower Walden products indicated less salt dissociation in the 5EC:3PC:2DEC and 5EC:3PC:2DEC + 2 wt.% electrolytes. NMR D19F and 23Na values for these electrolytes were also similar at 298K indicating cation-anion association, but diverged with increasing temperatures, with that for the anion being greater than the cation. The addition of the FEC provides greater local dynamics for the individual solvents in the less polar electrolyte but appeared to impede that of the ions.

Nuclear magnetic resonance spin-lattice relaxation of lithium ions in aqueous solution by NMR and molecular dynamics.

We study the aqueous solvation dynamics of lithium ions using nuclear magnetic resonance spectroscopy, molecular dynamics, and viscosity measurements. Several relaxation mechanisms are examined to explain the strong increases of spin-lattice relaxation toward high concentrations. The use of both 6Li and 7Li isotopes is helpful to identify the quadrupolar contribution to the relaxation rate. In particular, it is found that the quadrupolar interaction constitutes the strongest contribution above a concentration of ∼10 molal. The next-strongest contribution arises from interactions that scale with the square of the gyromagnetic ratio (mostly the dipolar interaction), and the experimental relaxation rates appear to be fully accounted for when these mechanisms are combined over the concentration range up to the saturation concentration. The study of solvation dynamics, particularly at high concentrations, could be of relevance for electrolyte dynamics in aqueous Li-ion rechargeable batteries.

Heterogeneous Structures of Ionic Liquids as Probed by CO Rotation with Nuclear Magnetic Resonance Relaxation Analysis and Molecular Dynamics Simulations.

The rotational dynamics of carbon monoxide (CO) in ionic liquids (ILs) was investigated by nuclear magnetic resonance (NMR) relaxation measurements and molecular dynamics (MD) simulations. NMR spin-lattice relaxation time measurements were performed for 17O-enriched CO in 10 ILs (four imidazolium-cation-based, four phosphonium-cation-based, and two ammonium-cation-based ILs, all paired with the bis(trifluorosulfonylmethane)imide anion). In combination with previously reported data for five ILs and viscosity data, our results indicated that the obtained rotational relaxation times (τ2R) were much smaller than those predicted using the Stokes-Einstein-Debye (SED) theory. For the same viscosity/temperature values, the τ2R-1 value increased linearly with increasing carbon number of the alkyl group in the cation. The deviation from the SED equation was due to the insensitivity of τ2R to the carbon number, even though a higher carbon number generally leads to higher viscosity values for ILs. To investigate the unique rotational properties of CO in the ILs, MD simulations were performed on five representative ILs (two imidazolium, two phosphonium, and one ammonium) containing CO solutes. From rotational correlation function analyses, the CO rotation mainly occurred in a free rotation-like manner within 1 ps, which explained the relative insensitivity of CO rotation to viscosity. In the subsequent time scale (>1 ps), the minor component of the CO rotation was discriminated among different ILs. It was strongly suggested that, because CO preferably locates in the outer part of the alkyl groups in the cation, the slow CO rotation is correlated with the outer alkyl dynamics, which are decoupled from the whole cation rotation.

Continuous Matrix Product Operator Approach to Finite Temperature Quantum States.

We present an algorithm for studying quantum systems at finite temperature using continuous matrix product operator representation. The approach handles both short-range and long-range interactions in the thermodynamic limit without incurring any time discretization error. Moreover, the approach provides direct access to physical observables including the specific heat, local susceptibility, and local spectral functions. After verifying the method using the prototypical quantum XXZ chains, we apply it to quantum Ising models with power-law decaying interactions and on the infinite cylinder, respectively. The approach offers predictions that are relevant to experiments in quantum simulators and the nuclear magnetic resonance spin-lattice relaxation rate.

Superconductivity of underdoped PrFeAs(O,F) investigated via point-contact spectroscopy and nuclear magnetic resonance

Underdoped PrFeAs(O,F), one of the less known members of the 1111 family of iron-based superconductors, was investigated in detail by means of transport, SQUID magnetometry, nuclear magnetic resonance (NMR) measurements and point-contact Andreev-reflection spectroscopy (PCARS). PCARS measurements on single crystals evidence the multigap nature of PrFeAs(O,F) superconductivity, shown to host at least two isotropic gaps, clearly discernible in the spectra, irrespective of the direction of current injection (i.e., along the ab planes or along the c axis). Additional features at higher energy can be interpreted as signatures of a strong electron-boson coupling, as demonstrated by a model which combines Andreev reflection with the Eliashberg theory. Magnetic resonance measurements in the normal phase indicate the lack of a magnetic order in underdoped PrFeAs(O,F), while $^{75}$As NMR spin-lattice relaxation results suggest the presence of significant electronic spin fluctuations, peaking above $T_{c}$ and expected to mediate the superconducting pairing.

Spin- 12 chain compound Ba2Cu2Te2P2O13 : Magnetization, specific heat, and local-probe NMR

We present synthesis and characterization of ${\mathrm{Ba}}_{2}{\mathrm{Cu}}_{2}{\mathrm{Te}}_{2}{\mathrm{P}}_{2}{\mathrm{O}}_{13}$ (BCTPO) via x-ray diffraction, magnetic susceptibility, heat capacity, and $^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) measurements. BCTPO crystallizes in a monoclinic structure with ${\mathrm{Cu}}^{2+}$ ions forming coupled chains. In magnetization $M(T)$ measurements, a broad maximum is observed around 53 K. Upon the application of magnetic fields, a sharp anomaly evolves around 4 K in the heat capacity ${C}_{P}(T)$ data, indicative of long-range order, while it is absent in zero field. The $^{31}\mathrm{P}$ NMR line shift at about 93.954 kOe tracks the spin susceptibility, whereas the line broadening evidences the onset of magnetic order at about 4 K or lower. The inferred isotropic and axial components of the hyperfine coupling constant are ${A}_{hf}^{\mathrm{iso}}\ensuremath{\simeq}$ 3635 $\text{Oe}/{\ensuremath{\mu}}_{B}$ and ${A}_{hf}^{ax}\ensuremath{\simeq}$ 479 $\text{Oe}/{\ensuremath{\mu}}_{B}$, respectively. The $^{31}\mathrm{P}$ NMR spin-lattice relaxation rate $1/{T}_{1}$ shows a pronounced divergence for $T\ensuremath{\longrightarrow}0$. We assign this behavior to critical fluctuations on the verge of order.

Li-Ion Diffusion in Nanoconfined LiBH4-LiI/Al2O3: From 2D Bulk Transport to 3D Long-Range Interfacial Dynamics.

Solid electrolytes based on LiBH4 receive much attention because of their high ionic conductivity, electrochemical robustness, and low interfacial resistance against Li metal. The highly conductive hexagonal modification of LiBH4 can be stabilized via the incorporation of LiI. If the resulting LiBH4-LiI is confined to the nanopores of an oxide, such as Al2O3, interface-engineered LiBH4-LiI/Al2O3 is obtained that revealed promising properties as a solid electrolyte. The underlying principles of Li+ conduction in such a nanocomposite are, however, far from being understood completely. Here, we used broadband conductivity spectroscopy and 1H, 6Li, 7Li, 11B, and 27Al nuclear magnetic resonance (NMR) to study structural and dynamic features of nanoconfined LiBH4-LiI/Al2O3. In particular, diffusion-induced 1H, 7Li, and 11B NMR spin–lattice relaxation measurements and 7Li-pulsed field gradient (PFG) NMR experiments were used to extract activation energies and diffusion coefficients. 27Al magic angle spinning NMR revealed surface interactions of LiBH4-LiI with pentacoordinated Al sites, and two-component 1H NMR line shapes clearly revealed heterogeneous dynamic processes. These results show that interfacial regions have a determining influence on overall ionic transport (0.1 mS cm–1 at 293 K). Importantly, electrical relaxation in the LiBH4-LiI regions turned out to be fully homogenous. This view is supported by 7Li NMR results, which can be interpreted with an overall (averaged) spin ensemble subjected to uniform dipolar magnetic and quadrupolar electric interactions. Finally, broadband conductivity spectroscopy gives strong evidence for 2D ionic transport in the LiBH4-LiI bulk regions which we observed over a dynamic range of 8 orders of magnitude. Macroscopic diffusion coefficients from PFG NMR agree with those estimated from measurements of ionic conductivity and nuclear spin relaxation. The resulting 3D ionic transport in nanoconfined LiBH4-LiI/Al2O3 is characterized by an activation energy of 0.43 eV.

Lithium-Ion Transport in Nanocrystalline Spinel-Type Li[InxLiy]Br4 as Seen by Conductivity Spectroscopy and NMR.

Currently, a variety of solid Li+ conductors are being discussed that could potentially serve as electrolytes in all-solid-state Li-ion batteries and batteries using metallic Li as the anode. Besides oxides, sulfides and thioposphates, and also halogenides, such as Li3YBr6, belong to the group of such promising materials. Here, we report on the mechanosynthesis of ternary, nanocrystalline (defect-rich) Li[InxLiy]Br4, which crystallizes with a spinel structure. We took advantage of a soft mechanochemical synthesis route that overcomes the limitations of classical solid-state routes, which usually require high temperatures to prepare the product. X-ray powder diffraction, combined with Rietveld analysis, was used to collect initial information about the crystal structure; it turned out that the lithium indium bromide prepared adopts cubic symmetry (). The overall and electronic conductivity were examined via broadband conductivity spectroscopy and electrical polarization measurements. While electric modulus spectroscopy yielded information on long-range ion transport, 7Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements revealed rapid, localized ionic hopping processes in the ternary bromide. Finally, we studied the influence of thermal treatment on overall conductivity, as the indium bromide might find applications in cells that are operated at high temperatures (330 K and above).

Proton dynamics in antiferroelectric CsH3(SeO3)2 single crystal investigated by 1H NMR measurements

1H nuclear magnetic resonance (NMR) measurements have been performed to study the proton dynamics associated with the antiferroelectric transition of a hydrogen-bonded single crystal of CsH3(SeO3)2. Herein, 1H NMR spectrum, shift, linewidth, and spin-lattice relaxation rate 1/T1 are measured in the temperature range of 80–296 K with the c-axis parallel to a magnetic field of ~4.85 T. The spectrum exhibits a composite structure with two narrow peaks at 296 K; at a low temperature, this structure evolves into a single broad shape with three humps. This complex shape and evolution are deconvoluted into five or six components based on the number of inequivalent and disordered hydrogen sites. By estimating the chemical shift and linewidth for each proton site, we identify all peaks. The spin-lattice relaxation recovery exhibits a double-exponential behavior with two relaxation times, short T1S and extremely large T1L. Both T1S and T1L follow Arrhenius behavior. From the respective 1/T1(T), the activation energies for proton motion are measured to be small: 1.16 ± 0.1 and 0.83 ± 0.06 kJ/mol for T1S and T1L, respectively. While the static NMR data, chemical shift and linewidth, show no evidence for the transition, the dynamic data 1/T1L highlights a clear increase across TN = 145 K, which is possibly a signature of the transition.

Motional freedom of dimethylammonium ions in a cyanoelpasolite, [(CH3)2NH2]2KCo(CN)6, which exhibits phase transition associated with a distinct change in dielectric property.

The temperature dependence of the 1H nuclear magnetic resonance spin-lattice relaxation time T1 of [(CH3)2NH2]2KCo(CN)6 and the partially deuterated analogue [(CD3)2NH2]2KCo(CN)6 has been reported. A change in the molecular motion of organic cations through the first-order phase transition at Tc = 246 K has been discussed. Although this first-order transition has been reported as an isosymmetric transition, in which the space group of the crystal does not change, the number of the 14N nuclear quadrupole resonance line changed from three in the high-temperature phase to twelve in the low-temperature phase indicating the lowering of crystal symmetry.

Self-diffusion and ionic exchange in mechanosynthesized, nanocrystalline solid solutions of PbF2 and CaF2[sbnd]19F 2D NMR visualizes the flourine hopping preferences

Ionic conductors based on PbF2, being one of the archetypes to study ion dynamics, serve as excellent model substances to study the elementary steps of translational anion dynamics in the solid state. Here, high-energy ball milling was employed to prepare a structurally disordered, metastable solid solution by mixing PbF2 with CaF2. The cation-mixed lattice in cubic Ca0.4Pb0.6F2 provides a range of magnetically distinct fluorine sites. We used 2D 19F magic angle spinning nuclear magnetic resonance (NMR) exchange spectroscopy to reveal the site preference of the F anions when hopping through the lattice. It turned out that the F anions located in sites coordinated by Pb cations are more mobile than those residing near or in Ca-rich environments. Conductivity measurements and variable-temperature 19F NMR spin-lattice relaxation experiments provide activation energies (0.24 eV, 0.40 eV) from which we deduce that in cation-mixed Ca0.4Pb0.6F2 anion diffusivity, on the angstrom length-scale, is mainly determined by vacant F− sites. Macroscopic ion transport has to be characterized by an activation energy of 0.55 eV suggesting that the F anions also use interstitial sites for long-range ionic transport.