I11-High Resolution Powder Diffraction
|
Bernhard T.
Leube
,
Christopher M.
Collins
,
Luke M.
Daniels
,
Benjamin B.
Duff
,
Yun
Dang
,
Ruiyong
Chen
,
Michael W.
Gaultois
,
Troy D.
Manning
,
Frédéric
Blanc
,
Matthew S.
Dyer
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[17193]
Open Access
Abstract: A tetragonal argyrodite with >7 mobile cations, Li7Zn0.5SiS6, is experimentally realized for the first time through solid state synthesis and exploration of the Li–Zn–Si–S phase diagram. The crystal structure of Li7Zn0.5SiS6 was solved ab initio from high-resolution X-ray and neutron powder diffraction data and supported by solid-state NMR. Li7Zn0.5SiS6 adopts a tetragonal I4 structure at room temperature with ordered Li and Zn positions and undergoes a transition above 411.1 K to a higher symmetry disordered F43m structure more typical of Li-containing argyrodites. Simultaneous occupation of four types of Li site (T5, T5a, T2, T4) at high temperature and five types of Li site (T5, T2, T4, T1, and a new trigonal planar T2a position) at room temperature is observed. This combination of sites forms interconnected Li pathways driven by the incorporation of Zn2+ into the Li sublattice and enables a range of possible jump processes. Zn2+ occupies the 48h T5 site in the high-temperature F43m structure, and a unique ordering pattern emerges in which only a subset of these T5 sites are occupied at room temperature in I4 Li7Zn0.5SiS6. The ionic conductivity, examined via AC impedance spectroscopy and VT-NMR, is 1.0(2) × 10–7 S cm–1 at room temperature and 4.3(4) × 10–4 S cm–1 at 503 K. The transition between the ordered I4 and disordered F43m structures is associated with a dramatic decrease in activation energy to 0.34(1) eV above 411 K. The incorporation of a small amount of Zn2+ exercises dramatic control of Li order in Li7Zn0.5SiS6 yielding a previously unseen distribution of Li sites, expanding our understanding of structure–property relationships in argyrodite materials.
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Apr 2022
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I11-High Resolution Powder Diffraction
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Open Access
Abstract: Mixed anion materials and anion doping are very promising strategies to improve solid-state electrolyte properties by enabling an optimized balance between good electrochemical stability and high ionic conductivity. In this work, we present the discovery of a novel lithium aluminum sulfide–chloride phase, obtained by substitution of chloride for sulfur in Li3AlS3 and Li5AlS4 materials. The structure is strongly affected by the presence of chloride anions on the sulfur site, as the substitution was shown to be directly responsible for the stabilization of a higher symmetry phase presenting a large degree of cationic site disorder, as well as disordered octahedral lithium vacancies. The effect of disorder on the lithium conductivity properties was assessed by a combined experimental–theoretical approach. In particular, the conductivity is increased by a factor 103 compared to the pure sulfide phase. Although it remains moderate (10–6 S·cm–1), ab initio molecular dynamics and maximum entropy (applied to neutron diffraction data) methods show that disorder leads to a 3D diffusion pathway, where Li atoms move thanks to a concerted mechanism. An understanding of the structure–property relationships is developed to determine the limiting factor governing lithium ion conductivity. This analysis, added to the strong step forward obtained in the determination of the dimensionality of diffusion, paves the way for accessing even higher conductivity in materials comprising an hcp anion arrangement.
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Nov 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[18630]
Open Access
Abstract: The structures of Zr and Hf metal–organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M6 cluster (as in fcu UiO-66) to the hcp-characteristic M12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species.
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Nov 2021
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I11-High Resolution Powder Diffraction
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Open Access
Abstract: We report a metal-organic framework where an ordered array of two linkers with differing length and geometry connect [Zr 6 (OH) 4 O 4 ] 12+ clusters into a twelve-connected fcu net that is rhombohedrally distorted from cubic symmetry. The ordered binding of equal numbers of terephthalate and fumarate ditopic carboxylate linkers at the trigonal antiprismatic Zr 6 core creates close-packed layers of fumarate-connected clusters that are connected along the single remaining threefold axis by terephthalates. This well-defined linker arrangement retains the three-dimensional porosity of the Zr cluster-based UiO family while creating two distinct windows within the channels that define two distinct guest diffusion paths. The ordered material is accessed by a restricted combination of composition and process parameters that were identified by high-throughput synthesis.
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Sep 2021
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I11-High Resolution Powder Diffraction
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Andrij
Vasylenko
,
Jacinthe
Gamon
,
Benjamin B.
Duff
,
Vladimir V.
Gusev
,
Luke M.
Daniels
,
Marco
Zanella
,
J. Felix
Shin
,
Paul M.
Sharp
,
Alexandra
Morscher
,
Ruiyong
Chen
,
Alex R.
Neale
,
Laurence J.
Hardwick
,
John B.
Claridge
,
Frédéric
Blanc
,
Michael W.
Gaultois
,
Matthew S.
Dyer
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[23666]
Open Access
Abstract: The selection of the elements to combine delimits the possible outcomes of synthetic chemistry because it determines the range of compositions and structures, and thus properties, that can arise. For example, in the solid state, the elemental components of a phase field will determine the likelihood of finding a new crystalline material. Researchers make these choices based on their understanding of chemical structure and bonding. Extensive data are available on those element combinations that produce synthetically isolable materials, but it is difficult to assimilate the scale of this information to guide selection from the diversity of potential new chemistries. Here, we show that unsupervised machine learning captures the complex patterns of similarity between element combinations that afford reported crystalline inorganic materials. This model guides prioritisation of quaternary phase fields containing two anions for synthetic exploration to identify lithium solid electrolytes in a collaborative workflow that leads to the discovery of Li3.3SnS3.3Cl0.7. The interstitial site occupancy combination in this defect stuffed wurtzite enables a low-barrier ion transport pathway in hexagonal close-packing.
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Sep 2021
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I11-High Resolution Powder Diffraction
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Christopher M.
Collins
,
Luke M.
Daniels
,
Quinn
Gibson
,
Michael W.
Gaultois
,
Michael
Moran
,
Richard
Feetham
,
Michael J.
Pitcher
,
Matthew S
Dyer
,
Charlene
Delacotte
,
Marco
Zanella
,
Claire A.
Murray
,
Gyorgyi
Glodan
,
Olivier
Perez
,
Denis
Pelloquin
,
Troy D.
Manning
,
Jonathan
Alaria
,
George R.
Darling
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Open Access
Abstract: We report the aperiodic titanate Ba 10 Y 6 Ti 4 O 27 with a room temperature thermal conductivity that equals the lowest reported for an oxide. The structure is characterised by discontinuous occupancy modulation of each of the sites, and can be considered as a quasicrystal. The resulting localisation of lattice vibrations suppresses phonon transport of heat. This new lead material for low thermal conductivity oxides is metastable and located within a quaternary phase field that has been previously explored – its isolation thus requires a precisely‐defined synthetic protocol. The necessary narrowing of the search space for experimental investigation is achieved by evaluation of titanate crystal chemistry, prediction of unexplored structural motifs that will favour synthetically accessible new compositions and assessment of their properties with machine learning models.
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May 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[16536]
Abstract: Neutron diffraction and x-ray pair distribution function experiments were performed to investigate the magnetic and local crystal structures of
Ba
2
FeSb
Se
5
and to compare them with the average (i.e., long range) structural model previously obtained by single-crystal x-ray diffraction. Changes in the local crystal structure (i.e., in the second coordination sphere) are observed upon cooling from 295 to 95 K, resulting in deviations from the average (i.e., long range) crystal structure. In this paper, we demonstrate that these observations cannot be explained by local or long-range magnetoelastic effects involving Fe-Fe correlations. Instead, we found that the observed differences between local and average crystal structure can be explained by Sb-
5
s
lone pair dynamics. We also find that, below the Néel temperature
(
T
N
=
58
K
)
, the two distinct magnetic
Fe
3
+
sites order collinearly, such that a combination of antiparallel and parallel spin arrangements along the
b
axis results. The nearest-neighbor arrangement
(
J
1
=
6
Å
)
is fully antiferromagnetic, while next-nearest-neighbor interactions are ferromagnetic in nature.
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Feb 2021
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I11-High Resolution Powder Diffraction
|
Jacinthe
Gamon
,
Benjamin B.
Duff
,
Matthew S.
Dyer
,
Christopher
Collins
,
Luke M.
Daniels
,
T. Wesley
Surta
,
Paul M.
Sharp
,
Michael W.
Gaultois
,
Frédéric
Blanc
,
John B.
Claridge
,
Matthew
Rosseinsky
Open Access
Abstract: With the goal of finding new lithium solid electrolytes by a combined computational-experimental method, the exploration of the Li-Al-O-S phase field resulted in the discovery of a new sulphide Li3AlS3. The structure of the new phase was determined through an approach combining synchrotron X-ray and neutron diffraction with 6Li and 27Al magic angle spinning nuclear magnetic resonance spectroscopy, and revealed a highly ordered cationic polyhedral network within a sulphide anion hcp-type sublattice. The originality of the structure relies on the presence of Al2S6 repeating dimer units consisting of two edge-shared Al tetrahedra. We find that, in this structure type consisting of alternating tetrahedral layers with Li-only polyhedra layers, the formation of these dimers is constrained by the Al/S ratio of 1/3. Moreover, by comparing this structure to similar phases such as Li5AlS4 and Li4.4Al0.2Ge0.3S4 ((Al+Ge)/S = 1/4), we discovered that the Al2S6 dimers not only influence atomic displacements and Li polyhedral distortions, but also determine the overall Li polyhedral arrangement within the hcp lattice, leading to the presence of highly ordered vacancies in both the tetrahedral and Li-only layer. AC-impedance measurements revealed a low lithium mobility, which is strongly impacted by the presence of ordered vacancies. Finally, a composition-structure-property relationship understanding was developed to explain the extent of lithium mobility in this structure type.
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Oct 2019
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[13911]
Abstract: Materials used as electrodes in energy storage devices have been extensively studied with solid-state NMR spectroscopy. Due to the almost ubiquitous presence of transition metals, these systems are also often magnetic. While it is well known that the presence of anisotropic bulk magnetic susceptibility (ABMS) leads to broadening of resonances under MAS, we show that for mono-disperse and non-spherical particle morphologies, the ABMS can also lead to considerable shifts, which vary substantially as a function of particle shape. This, on one hand, complicates the interpretation of the NMR spectrum and the ability to compare the measured shift of different samples of the same system. On the other hand the ABMS shift provides a mechanism with which to derive the particle shape from the NMR spectrum. In this work, we present a methodology to model the ABMS shift, and relate it to the shape of the studied particles. The approach is tested on the $^7$Li NMR spectra of single crystals and powders of LiFePO$_4$. The results show that the ABMS shift can be a major contribution to the total NMR shift in systems with large magnetic anisotropies and small hyperfine shifts, $^7$Li shifts for typical LiFePO$_4$ morphologies varying by as much as 100 ppm. The results are generalised to demonstrate that the approach can be used as a means with which to probe the aspect ratio of particles. The work has implications for the analysis of NMR spectra of all materials with anisotropic magnetic susceptibilities, including diamagnetic materials such as graphite.
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Jul 2019
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[19080]
Abstract: The metal-free hybrid organic–inorganic perovskite [MDABCO](NH4)I3 (with MDABCO = N-methyl-1,4-diazabicyclo[2.2.2]octane) was recently discovered to exhibit an excellent ferroelectric performance, challenging established ceramic ferroelectrics. We here probe the mechanical properties of [MDABCO](NH4)I3 by combining high pressure single crystal X-ray diffraction and nanoindentation, underlining the exceptional role and opportunities that come with the use of sustainable, metal-free perovskite ferroelectrics.
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Mar 2019
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