I09-Surface and Interface Structural Analysis
|
Galo J.
Paez
,
Christopher N.
Singh
,
Matthew J.
Wahila
,
Keith E.
Tirpak
,
Nicholas F.
Quackenbush
,
Shawn
Sallis
,
Hanjong
Paik
,
Yufeng
Liang
,
Darrell G.
Schlom
,
Tien-Lin
Lee
,
Christoph
Schlueter
,
Wei-Cheng
Lee
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[13812, 25355]
Abstract: Recent reports have identified new metaphases of
VO
2
with strain and/or doping, suggesting the structural phase transition and the metal-to-insulator transition might be decoupled. Using epitaxially strained
VO
2
/
Ti
O
2
(001) thin films, which display a bulklike abrupt metal-to-insulator transition and rutile to monoclinic transition structural phase transition, we employ x-ray standing waves combined with hard x-ray photoelectron spectroscopy to simultaneously measure the structural and electronic transitions. This x-ray standing waves study elegantly demonstrates the structural and electronic transitions occur concurrently within experimental limits (±1K).
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May 2020
|
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I09-Surface and Interface Structural Analysis
|
Matthew J.
Wahila
,
Galo
Paez
,
Christopher N.
Singh
,
Anna
Regoutz
,
Shawn
Sallis
,
Mateusz J.
Zuba
,
Jatinkumar
Rana
,
M. Brooks
Tellekamp
,
Jos E.
Boschker
,
Toni
Markurt
,
Jack E. N.
Swallow
,
Leanne A. H.
Jones
,
Tim D.
Veal
,
Wanli
Yang
,
Tien-Lin
Lee
,
Fanny
Rodolakis
,
Jerzy T.
Sadowski
,
David
Prendergast
,
Wei-Cheng
Lee
,
W. Alan
Doolittle
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[20647, 21430]
Abstract: The metal-insulator transition of
NbO
2
is thought to be important for the functioning of recent niobium oxide-based memristor devices, and is often described as a Mott transition in these contexts. However, the actual transition mechanism remains unclear, as current devices actually employ electroformed
NbO
x
that may be inherently different to crystalline
NbO
2
. We report on our synchrotron x-ray spectroscopy and density-functional-theory study of crystalline, epitaxial
NbO
2
thin films grown by pulsed laser deposition and molecular beam epitaxy across the metal-insulator transition at
∼
810
∘
C
. The observed spectral changes reveal a second-order Peierls transition driven by a weakening of Nb dimerization without significant electron correlations, further supported by our density-functional-theory modeling. Our findings indicate that employing crystalline
NbO
2
as an active layer in memristor devices may facilitate analog control of the resistivity, whereby Joule-heating can modulate Nb-Nb dimer distance and consequently control the opening of a pseudogap.
|
Jul 2019
|
|
I09-Surface and Interface Structural Analysis
|
Sebastian A.
Howard
,
Christopher N.
Singh
,
Galo J.
Paez
,
Matthew
Wahila
,
Linda W.
Wangoh
,
Shawn
Sallis
,
Keith
Tirpak
,
Yufeng
Liang
,
David
Prendergast
,
Mateusz
Zuba
,
Jatinkumar
Rana
,
Alex
Weidenbach
,
Timothy M.
Mccrone
,
Wanli
Yang
,
Tien-Lin
Lee
,
Fanny
Rodolakis
,
William
Doolittle
,
Wei-Cheng
Lee
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[20647]
Open Access
Abstract: The discovery of analog LixNbO2 memristors revealed a promising new memristive mechanism wherein the diffusion of Li+ rather than O2− ions enables precise control of the resistive states. However, directly correlating lithium concentration with changes to the electronic structure in active layers remains a challenge and is required to truly understand the underlying physics. Chemically delithiated single crystals of LiNbO2 present a model system for correlating lithium variation with spectroscopic signatures from operando soft x-ray spectroscopy studies of device active layers. Using electronic structure modeling of the x-ray spectroscopy of LixNbO2 single crystals, we demonstrate that the intrinsic memristive behavior in LixNbO2 active layers results from field-induced degenerate p-type doping. We show that electrical operation of LixNbO2-based memristors is viable even at marginal Li deficiency and that the analog memristive switching occurs well before the system is fully metallic. This study serves as a benchmark for material synthesis and characterization of future LixNbO2-based memristor devices and suggests that valence change switching is a scalable alternative that circumvents the electroforming typically required for filamentary-based memristors.
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Jul 2019
|
|
I09-Surface and Interface Structural Analysis
|
Zachary W.
Lebens-Higgins
,
Nicholas V.
Faenza
,
Maxwell D.
Radin
,
Hao
Liu
,
Shawn
Sallis
,
Jatinkumar
Rana
,
Julija
Vinckeviciute
,
Philip J.
Reeves
,
Mateusz
Zuba
,
Fadwa
Badway
,
Nathalie
Pereira
,
Karena W.
Chapman
,
Tien-Lin
Lee
,
Tianpin
Wu
,
Clare P.
Grey
,
Brent
Melot
,
Anton
Van Der Ven
,
Glenn G.
Amatucci
,
Wanli
Yang
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[19162]
Open Access
Abstract: Oxygen participation, arising from increased transition metal–oxygen covalency during delithiation, is considered essential for the description of charge compensation in conventional layered oxides. The advent of high-resolution mapping of the O K-edge resonant inelastic X-ray scattering (RIXS) provides an opportunity to revisit the onset and extent of oxygen participation. Combining RIXS with an array of structural and electronic probes for the family of Ni-rich LiNi0.8Co0.2−yAlyO2 cathodes, we identify common charge compensation regimes that are assigned to formal transition metal redox (<4.25 V) and oxygen participation through covalency (>4.25 V). From O K-edge RIXS maps, we find the emergence of a sharp RIXS feature in these systems when approaching full delithiation, which has previously been associated with lattice oxidized oxygen in alkali-rich systems. The lack of transition metal redox signatures and strong covalency at these high degrees of delithiation suggest this RIXS feature is similarly attributed to lattice oxygen charge compensation as in the alkali-rich systems. The RIXS feature's evolution with state of charge in conventional layered oxides is evidence that this feature reflects the depopulation of occupied O 2p states associated with oxygen participation.
|
Jul 2019
|
|
I09-Surface and Interface Structural Analysis
|
Zachary W.
Lebens-Higgins
,
Shawn
Sallis
,
Nicholas V.
Faenza
,
Fadwa
Badway
,
Nathalie
Pereira
,
David M.
Halat
,
Matthew
Wahila
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
Wanli
Yang
,
Clare P.
Grey
,
Glenn G.
Amatucci
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[12764, 16005]
Abstract: For layered oxide cathodes, impedance growth and capacity fade related to reactions at the cathode-electrolyte interface (CEI) are particularly prevalent at high voltage and high temperatures. At a minimum, the CEI layer consists of Li2CO3, LiF, reduced (relative to the bulk) metal-ion species, and salt decomposition species but conflicting reports exist regarding their progression during (dis)charging. Utilizing transport measurements in combination with x-ray and nuclear magnetic resonance spectroscopy techniques, we study the evolution of these CEI species as a function of electrochemical and thermal stress for LiNi0.8Co0.15Al0.05O2 (NCA) particle electrodes using a LiPF6 ethylene carbonate: dimethyl carbonate (1:1 volume ratio) electrolyte. Although initial surface metal reduction does correlate with surface Li2CO3 and LiF, these species are found to decompose upon charging and are absent above 4.25 V. While there is trace LiPF6 breakdown at room temperature above 4.25 V, thermal aggravation is found to strongly promote salt breakdown and contributes to surface degradation even at lower voltages (4.1 V). An interesting finding of our work was the partial reformation of LiF upon discharge which warrants further consideration for understanding CEI stability during cycling.
|
Jan 2018
|
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I09-Surface and Interface Structural Analysis
|
Zachary W.
Lebens-Higgins
,
Nicholas
Faenza
,
Pinaki
Mukherjee
,
Shawn
Sallis
,
Fadwa
Badway
,
Nathalie
Pereira
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
Frederic
Cosandey
,
Glenn
Amatucci
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[12764, 16005]
Abstract: For layered oxide cathodes, aluminum doping has widely been shown to improve performance, particularly at high degrees of delithiation. While this has led to increased interest in Al-doped systems, including LiNi0.8Co0.15Al0.05O2 (NCA), the aluminum surface environment has not been thoroughly investigated. Using hard x-ray photoelectron spectroscopy measurements of the Al 1s core region for NCA electrodes, we examined the evolution of the surface aluminum environment under electrochemical and thermal stress. By correlating the aluminum environment to transition metal reduction and electrolyte decomposition, we provide further insight into the cathode-electrolyte interface layer. A remarkable finding is that Al-O coatings in LiPF6 electrolyte mimic the evolution observed for the aluminum surface environment in doped layered oxides.
|
Dec 2017
|
|
I09-Surface and Interface Structural Analysis
|
Nicholas V.
Faenza
,
Zachary W.
Lebens-Higgins
,
Pinaki
Mukherjee
,
Shawn
Sallis
,
Nathalie
Pereira
,
Fadwa
Badway
,
Anna
Halajko
,
Gerbrand
Ceder
,
Frederic
Cosandey
,
Louis F. J.
Piper
,
Glenn G.
Amatucci
Diamond Proposal Number(s):
[12764]
Abstract: Enabling practical utilization of layered R-3m positive electrodes near full delithiation requires an enhanced understanding of the complex electrode-electrolyte interactions that often induce failure. Using Li[Ni0.8Co0.15Al0.05]O2 (NCA) as a model layered compound, the chemical and structural stability in a strenuous thermal and electrochemical environment was explored. Operando microcalorimetry and electrochemical impedance spectroscopy identified a fingerprint for a structural decomposition and transition metal dissolution reaction that occurs on the positive electrode at full delithiation. Surface sensitive characterization techniques, including X-ray absorption spectroscopy and high resolution transmission electron microscopy, measured a structural and morphological transformation of the surface and subsurface regions of NCA. Despite the bulk structural integrity being maintained, NCA surface degradation at a high state of charge induces excessive transition metal dissolution and significant positive electrode impedance development, resulting in a rapid decrease of electrochemical performance. Additionally, the impact of electrolyte salt, positive electrode surface area, and surface Li2CO3 content on the magnitude and character of the dissolution reaction was studied.
|
Jun 2017
|
|
I09-Surface and Interface Structural Analysis
|
Nicholas
Quackenbush
,
H.
Paik
,
Matthew
Wahila
,
Shawn
Sallis
,
M. E.
Holtz
,
X.
Huang
,
A.
Ganose
,
B. J.
Morgan
,
David O.
Scanlon
,
Y.
Gu
,
F.
Xue
,
L.-Q.
Chen
,
G. E.
Sterbinsky
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
J. C.
Woicik
,
J.-H.
Guo
,
J. D.
Brock
,
D. A.
Muller
,
D. A.
Arena
,
D. G.
Schlom
,
Louis
Piper
Diamond Proposal Number(s):
[12546]
Abstract: Tensile strain along the cR axis in epitaxial VO2 films raises the temperature of the metal insulator transition and is expected to stabilize the intermediate monoclinic M2 phase. We employ surface-sensitive x-ray spectroscopy to distinguish from the TiO2 substrate and identify the phases of VO2 as a function of temperature in epitaxial VO2/TiO2 thin films with well-defined biaxial strain. Although qualitatively similar to our Landau-Ginzburg theory predicted phase diagrams, the M2 phase is stabilized by nearly an order of magnitude more strain than expected for the measured temperature window. Our results reveal that the elongation of the cR axis is insufficient for describing the transition pathway of VO2 epitaxial films and that a strain induced increase of electron correlation effects must be considered.
|
Aug 2016
|
|
I09-Surface and Interface Structural Analysis
|
Linda W.
Wangoh
,
Shawn
Sallis
,
Kamila M.
Wiaderek
,
Yuh-Chieh
Lin
,
Bohua
Wen
,
Nicholas
Quackenbush
,
Natasha A.
Chernova
,
Jinghua
Guo
,
Lu
Ma
,
Tianpin
Wu
,
Tien-Lin
Lee
,
Christoph
Schlueter
,
Shyue Ping
Ong
,
Karena W.
Chapman
,
M. Stanley
Whittingham
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[11246, 12546]
Abstract: Full, reversible intercalation of two Li+ has not yet been achieved in promising VOPO4 electrodes. A
pronounced Li+ gradient has been reported in the low voltage window (i.e., second lithium reaction)
that is thought to originate from disrupted kinetics in the high voltage regime (i.e., first lithium
reaction). Here, we employ a combination of hard and soft x–ray photoelectron and absorption
spectroscopy techniques to depth profile solid state synthesized LiVOPO4 cycled within the low
voltage window only. Analysis of the vanadium environment revealed no evidence of a Li+ gradient,
which combined with almost full theoretical capacity confirms that disrupted kinetics in the high
voltage window are responsible for hindering full two lithium insertion. Furthermore, we argue that
the uniform Li+ intercalation is a prerequisite for the formation of intermediate phases Li1.50VOPO4
and Li1.75VOPO4. The evolution from LiVOPO4 to Li2VOPO4 via the intermediate phases is
confirmed by direct comparison between O K–edge absorption spectroscopy and density functional
theory.
|
Aug 2016
|
|
I09-Surface and Interface Structural Analysis
|
Shawn
Sallis
,
N.
Pereira
,
P.
Mukherjee
,
Nicholas
Quackenbush
,
N.
Faenza
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
W. L.
Yang
,
F.
Cosandey
,
G. G.
Amatucci
,
Louis
Piper
Diamond Proposal Number(s):
[12764]
Abstract: The pronounced capacity fade in Ni-rich layered oxide lithium ion battery cathodes observed when cycling above 4.1 V (versus Li/Li+) is associated with a rise in impedance, which is thought to be due to either bulk structural fatigue or surface reactions with the electrolyte (or combination of both). Here, we examine the surface reactions at electrochemically stressed Li1– x Ni 0.8Co0.15Al0.05O2 binder-free powder electrodes with a combination of electrochemical impedance spectroscopy, spatially resolving electron microscopy, and spatially averaging X-ray spectroscopy techniques. We circumvent issues associated with cycling by holding our electrodes at high states of charge (4.1 V, 4.5 V, and 4.75 V) for extended periods and correlate charge-transfer impedance rises observed at high voltages with surface modifications retained in the discharged state (2.7 V). The surface modifications involve significant cation migration (and disorder) along with Ni and Co reduction, and can occur even in the absence of significant Li2CO3 and LiF. These data provide evidence that surface oxygen loss at the highest levels of Li+ extraction is driving the rise in impedance.
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Jun 2016
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