I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[25166]
Open Access
Abstract: We report the synthesis, crystal structure, thermal response, and electrochemical behavior of the Prussian blue analogue (PBA) K2Cu[Fe(CN)6]. From a structural perspective, this is the most complex PBA yet characterized: its triclinic crystal structure results from an interplay of cooperative Jahn–Teller order, octahedral tilts, and a collective “slide” distortion involving K-ion displacements. These different distortions give rise to two crystallographically distinct K-ion channels with different mobilities. Variable-temperature X-ray powder diffraction measurements show that K-ion slides are the lowest-energy distortion mechanism at play, as they are the only distortion to be switched off with increasing temperature. Electrochemically, the material operates as a K-ion cathode with a high operating voltage and an improved initial capacity relative to higher-vacancy PBA alternatives. On charging, K+ ions are selectively removed from a single K-ion channel type, and the slide distortions are again switched on and off accordingly. We discuss the functional importance of various aspects of structural complexity in this system, placing our discussion in the context of other related PBAs.
|
May 2022
|
|
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.
|
Apr 2022
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[28349]
Abstract: Frustrated lanthanide oxides with dense magnetic lattices are of fundamental interest for their potential in cryogenic refrigeration due to a large ground state entropy and suppressed ordering temperatures but can often be limited by short-range correlations. Here, we present examples of frustrated fcc oxides, Ba2GdSbO6 and Sr2GdSbO6, and the new site-disordered analogue Ca2GdSbO6 ([CaGd]A[CaSb]BO6), in which the magnetocaloric effect is influenced by minimal superexchange (J1 ∼ 10 mK). We report on the crystal structures using powder X-ray diffraction and the bulk magnetic properties through low-field susceptibility and isothermal magnetization measurements. The Gd compounds exhibit a magnetic entropy change of up to −15.8 J/K/molGd in a field of 7 T at 2 K, a 20% excess compared to the value of −13.0 J/K/molGd for a standard in magnetic refrigeration, Gd3Ga5O12. Heat capacity measurements indicate a lack of magnetic ordering down to 0.4 K for Ba2GdSbO6 and Sr2GdSbO6, suggesting cooling down through the liquid 4-He regime. A mean-field model is used to elucidate the role of primarily free-spin behavior in the magnetocaloric performance of these compounds in comparison to other top-performing Gd-based oxides. The chemical flexibility of the double perovskites raises the possibility of further enhancement of the magnetocaloric effect in the Gd3+fcc lattices.
|
Mar 2022
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[24332]
Abstract: Highly conductive solid electrolytes are fundamental for all solid-state batteries with low inner cell resistance. Such fast solid electrolytes are often found by systematic substitution experiments in which one atom is exchanged for another, and corresponding changes in ionic transport are monitored. With this strategy, compositions with the most promising transport properties can be identified fast and reliably. However, the substitution of one element does not only influence the crystal structure and diffusion channel size (static) but also the underlying bonding interactions and with it the vibrational properties of the lattice (dynamic). Since both static and dynamic properties influence the diffusion process, simple one-dimensional substitution series only provide limited insights to the importance of changes in the structure and lattice dynamics for the transport properties. To overcome these limitations, we make use of a two-dimensional substitution approach, investigating and comparing the four single-substitution series Na3P1–xSbxS4, Na3P1–xSbxSe4, Na3PS4–ySey, and Na3SbS4–ySey. Specifically, we find that the diffusion channel size represented by the distance between S/Se ions cannot explain the observed changes of activation barriers throughout the whole substitution system. Melting temperatures and the herein newly defined anharmonic bulk modulus─as descriptors for bonding interactions and corresponding lattice dynamics─correlate well with the activation barriers, highlighting the relevance of lattice softness for the ion transport in this class of fast ion conductors.
|
Feb 2022
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[25166]
Abstract: Reaction between Na2FeSbO5 and LiNO3 at 300 °C yields the metastable phase Li2FeSbO5 which is isostructural with the sodium “parent” phase (space group Pbna, a = 15.138(1) Å, b = 5.1440(3) Å, c = 10.0936(6) Å) consisting of an alternating stack of Li2Fe2O5 and Li2Sb2O5 sheets containing tetrahedral coordinated Fe3+ and octahedrally coordinated Sb5+, respectively. Further reaction between Li2FeSbO5 with NO2BF4 in acetonitrile at room temperature yields LiFeSbO5, which adopts an orthorhombic structure (space group Pbn21, a = 14.2943(4) Å, b = 5.2771(1) Å, c = 9.5610(3) Å) in which the LiFeO5 layers have shifted on lithium extraction, resulting in an octahedral coordination for the iron cations. 57Fe Mössbauer data indicate that the nominal Fe4+ cations present in LiFeSbO5 have disproportionated into a 1:1 combination of Fe3+ and Fe5+ centers which are ordered within the LiFeSbO5 structural framework. It is widely observed that Fe4+ centers tend to be unstable in delithiated Li–Fe–X–O phases currently proposed as lithium-ion battery cathode materials, so the apparent stability of highly oxidized Fe5+ centers in LiFeSbO5 is notable, suggesting cathode materials based on oxidizing Fe3+ could be possible. However, in this instance, the structural change which occurs on delithiation of Li2FeSbO5 prevents electrochemical cycling of this material.
|
Feb 2022
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[21995, 26285]
Abstract: Ni-rich lithium nickel manganese cobalt (NMC) oxide cathode materials promise Li-ion batteries with increased energy density and lower cost. However, higher Ni content is accompanied by accelerated degradation and thus poor cycle lifetime, with the underlying mechanisms and their relative contributions still poorly understood. Here, we combine electrochemical analysis with surface-sensitive X-ray photoelectron and absorption spectroscopies to observe the interfacial degradation occurring in LiNi0.8Mn0.1Co0.1O2–graphite full cells over hundreds of cycles between fixed cell voltages (2.5–4.2 V). Capacity losses during the first ∼200 cycles are primarily attributable to a loss of active lithium through electrolyte reduction on the graphite anode, seen as thickening of the solid-electrolyte interphase (SEI). As a result, the cathode reaches ever-higher potentials at the end of charge, and with further cycling, a regime is entered where losses in accessible NMC capacity begin to limit cycle life. This is accompanied by accelerated transition-metal reduction at the NMC surface, thickening of the cathode electrolyte interphase, decomposition of residual lithium carbonate, and increased cell impedance. Transition-metal dissolution is also detected through increased incorporation into and thickening of the SEI, with Mn found to be initially most prevalent, while the proportion of Ni increases with cycling. The observed evolution of anode and cathode surface layers improves our understanding of the interconnected nature of the degradation occurring at each electrode and the impact on capacity retention, informing efforts to achieve a longer cycle lifetime in Ni-rich NMCs.
|
Feb 2022
|
|
I15-1-X-ray Pair Distribution Function (XPDF)
|
Alice M.
Bumstead
,
Ignas
Pakamore
,
Kieran D.
Richards
,
Michael F.
Thorne
,
Sophia S.
Boyadjieva
,
Celia
Castillo-Blas
,
Lauren N.
Mchugh
,
Adam F.
Sapnik
,
Dean S.
Keeble
,
David A.
Keen
,
Rachel C.
Evans
,
Ross S.
Forgan
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[20038]
Abstract: Melt-quenched metal–organic framework (MOF) glasses have gained significant interest as the first new category of glass reported in 50 years. In this work, an amine-functionalized zeolitic imidazolate framework (ZIF), denoted ZIF-UC-6, was prepared and demonstrated to undergo both melting and glass formation. The presence of an amine group resulted in a lower melting temperature compared to other ZIFs, while also allowing material properties to be tuned by post-synthetic modification (PSM). As a prototypical example, the ZIF glass surface was functionalized with octyl isocyanate, changing its behavior from hydrophilic to hydrophobic. PSM therefore provides a promising strategy for tuning the surface properties of MOF glasses.
|
Feb 2022
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[19772, 22706]
Open Access
Abstract: Reversible and irreversible charge exchange reactions of Li- and Mn-rich layered oxides (Li1.15Ni0.2Co0.1Mn0.55O2, LLO) are investigated with bulk and surface-sensitive near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the Ni L2,3, Co L2,3, Mn L2,3, and O K edges; mass spectrometry (MS); and operando synchrotron X-ray powder diffraction (SXPD). The present work shows the relation between O–O formation in the bulk and Ni, Co, and Mn reduction/oxidation processes, which in turn deliver outstanding capacities of Li-rich layered oxides (LLO). Moreover, the reversibility of charge compensation reactions is discussed and differences between O–O formation and oxygen release, both occurring mainly upon the first charge (so-called activation), are identified.
|
Dec 2021
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[24154]
Abstract: We present a comprehensive structural and magnetic characterization of the barlowite family of S = 1/2 kagomé magnets, Cu4(OH)6FX, where X = Cl, Br, or I. Through high-resolution synchrotron X-ray and neutron powder diffraction measurements, we reveal two sources of structural complexity within this family of materials, namely, compositional disorder of the halide species that occupy sites in between the kagomé layers and the positional disorder of the interlayer Cu2+ ions that persists well into the Pnma structural ground state. We demonstrate that understanding these inherent structural disorders is key as they correlate with the degree of partial order in the magnetic ground states of these quantum frustrated magnets.
|
Dec 2021
|
|
I11-High Resolution Powder Diffraction
|
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.
|
Nov 2021
|
|
