72 research outputs found
Negative muon spin rotation and relaxation on superconducting MgB2
The internal nuclear magnetic field in a superconducting MgB2 powder sample was studied with a μ- SR technique. Although the past μ +SR study on MgB2 reported the appearance of a dynamic behavior even below Tc due to μ + diffusion, μ- SR shows a static behavior in the whole temperature range measured, as expected. The ZF-μ- SR spectra do not suggest any appearance of additional magnetic field below Tc within the experimental accuracy. Considering the small asymmetry of the μ- SR signal, it is a challenge to detect the appearance of an internal magnetic field below Tc caused by the time reversal symmetry breaking
TRIM Simulations Tool for Stopping Fraction in Hydrostatic Pressure Cells
For quantum systems or materials, a common procedure for probing their
behaviour is to tune electronic/magnetic properties using external parameters,
e.g. temperature, magnetic field or pressure. Pressure application as an
external stimuli is a widely used tool, where the sample in question is
inserted into a pressure cell providing a hydrostatic pressure condition. Such
device causes some practical problems when using in Muon Spin
Rotation/Relaxation (SR) experiments as a large proportion of the muons
will be implanted in the pressure cell rather than in the sample, resulting in
a higher background signal. This issue gets further amplified when the
temperature dependent response from the sample is much smaller than that of the
pressure cell,which may cause the sample response to be lost in the background
and cause difficulties in aligning the sample within the beam. To tackle this
issue, we have used pySRIM to construct a practical and helpful simulation tool
for calculating muon stopping fractions, specifically for the pressure cell
setup at the E1 beamline using the GPD spectrometer at the Paul Scherrer
Institute, with the use of TRIM simulations. The program is used to estimate
the number of muon stopping in both the sample and the pressure cell at a given
momentum. The simulation tool is programmed into a GUI, making it accessible to
user to approximate prior to their experiments at GPD what fractions will
belong to the sample and the pressure cell in their fitting procedure.Comment: 8 Pages, 3 Figures, Conference proceedings for 15th international
conference on muon spin rotation, relaxation and resonanc
Confirming the high pressure phase diagram of the Shastry-Sutherland model
A Muon Spin Rotation (+SR) study was conducted to investigate the
magnetic properties of SrCu2(BO3)2 (SCBO) as a function of
temperature/pressure. Measurements in zero field and transverse field confirm
the absence of long range magnetic order at high pressures and low
temperatures. These measurements suggest changes in the Cu spin fluctuations
characteristics above 21 kbar, consistent with the formation of a plaquette
phase as previously suggested by inelastic neutron scattering measurements.
SCBO is the only known realisation of the Shatry-Sutherland model, thus the
ground state mediating the dimer and antiferromagnetic phase is likekly to be a
plaquette state
Acetic acid conversion to ketene on Cu2O(1 0 0): Reaction mechanism deduced from experimental observations and theoretical computations
Ketene, a versatile reagent in production of fine and specialty chemicals, is produced from acetic acid. We investigate the synthesis of ketene from acetic acid over the (3,0;1,1) surface of Cu2O(1 0 0) through analysis of the adsorption and desorption characteristics of formic and acetic acids. The results allow us to establish a reaction mechanism for ketene formation. Observations from x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy, and temperature programmed desorption (TPD), supported by a comparison with formic acid results, suggest that acetic acid reacts with Cu2O through deprotonation to form acetate species coordinated to copper sites and hydroxylation of nearby surface oxygen sites. For formic acid the decomposition of adsorbed formate species results in desorption of CO2 and CO while, for acetic acid, high yields of ketene are observed at temperature >500 K. Modeling by density functional theory (DFT) confirms the strong interaction of acetic acid with the (3,0;1,1) surface and the spontaneous dissociation into adsorbed acetate and hydrogen atom species, the latter forming an OH-group. In an identified reaction intermediate ketene binds via all C and O atoms to Cu surface sites, in agreement with interpretations from XPS. In the vicinity of the adsorbate the surface experiences a local reorganization into a c(2
7 2) reconstruction. The total computed energy barrier for ketene formation is 1.81 eV in good agreement with the 1.74 eV obtained from TPD analysis. Our experimental observations and mechanistic DFT studies suggests that Cu2O can operate as an efficient catalyst for the green generation of ketene from acetic acid
Confirming the high pressure phase diagram of the Shastry-Sutherland model
A Muon Spin Rotation (μ + SR) study was conducted to investigate the magnetic properties of SrCu2(BO3)2 (SCBO) as a function of temperature/pressure. Measurements in zero field and transverse field confirm the absence of long range magnetic order at high pressures and low temperatures. These measurements suggest changes in the Cu spin fluctuations characteristics above 21 kbar, consistent with the formation of a plaquette phase as previously suggested by inelastic neutron scattering measurements. SCBO is the only known realisation of the Shatry-Sutherland model, thus the ground state mediating the dimer and antiferromagnetic phase is likekly to be a plaquette state
High-Voltage Honeycomb Layered Oxide Positive Electrodes for Rechargeable Sodium Batteries
Natural abundance, impressive chemical characteristics and economic
feasibility have rekindled the appeal for rechargeable sodium (Na) batteries as
a practical solution for the growing energy demand, environmental
sustainability and energy independence. However, the scarcity of viable
positive electrode materials remains a huge impediment to the actualization of
this technology. In this paper, we explore honeycomb layered oxides adopting
the composition NaNiCoTeO ( and ) as
feasible positive electrode (cathode) materials for rechargeable sodium
batteries at both room- and elevated temperatures using ionic liquids. Through
standard galvanostatic assessments and analyses we demonstrate that
substitution of nickel with cobalt in NaNiTeO leads to an increase
in the discharge voltage to nearly V (versus Na / Na) for the
NaNiCoTeO family of honeycomb layered oxide materials,
which surpasses the attained average voltages for most layered oxide positive
electrode materials that facilitate Na-ion desertion. We also verify the
increased kinetics within the NaNiCoTeO honeycomb layered
oxides during operations at elevated temperatures which lead to an increase in
reversible capacity of the rechargeable Na battery. This study underpins the
doping of congener transition metal atoms to the honeycomb structure of
NaNiTeO in addition to elevated-temperature operation as a
judicious route to enhance the electrochemical performance of analogous layered
oxides.Comment: 16 pages, 4 figures, 1 cover art (Electronic Supplementary
Information: 10 pages, 5 figures, 3 tables
Search for a space charge layer in thin film battery materials with low-energy muons
In an all solid state Li-ion battery, it is crucial to reduce ionic resistivity at the interface between the electrode and the electrolyte in order to enhance Li+ mobility across the interface. Recent first principles calculations predict the presence of a space-charge layer (SCL) at the interface due to the difference in the Li+ chemical potential at the interface between two different materials, as in the metal-semiconductor junction in electronic devices. However, the presence of SCL has never been experimentally observed. Our first attempt in a fresh multilayer sample, Cu(10 nm)/Li3PO4(50 nm)/LiCoO2(100 nm) on a sapphire substrate, with low-energy μ +SR (LE μ +SR) revealed a gradual change in the nuclear magnetic field distribution width as a function of implantation depth even across the interface between Li3PO4 and LiCoO2. This implies that the change in the field distribution width at SCL of the sample is too small to be detected by LE μ +SR
Magnetic nature of wolframite MgReO
Rhenium oxides belonging to the family ReO where is a metal
cation, exhibit interesting electronic and magnetic properties. In this study
we have utilized the muon spin rotation/relaxation (SR) technique to
study the magnetic properties of the MgReO compound. To the best of our
knowledge, this is the first investigation reported on this interesting
material, that is stabilized in a wolframite crystal structure using a special
high-pressure synthesis technique. Bulk magnetic studies show the onset of an
antiferromagnetic (AF) long range order, or a possible singlet spin state at
~K, with a subtle second high-temperature transition at
~K. Both transitions are also confirmed by heat capacity
() measurements. From our SR measurements, it is clear that the
sample enters an AF order below ~K. We find no
evidence of magnetic signal above , which indicates that is likely linked to a structural transition. Further, via sensitive zero
field (ZF) SR measurements we find evidence of a spin reorientation at
~K. This points towards a transition from a collinear AF
into a canted AF order at low temperature, which is proposed to be driven by
competing magnetic interactions
Honeycomb layered oxides: Structure, energy storage, transport, topology and relevant insights
The advent of nanotechnology has hurtled the discovery and development of nanostructured materials with stellar chemical and physical functionalities in a bid to address issues in energy, environment, telecommunications and healthcare. In this quest, a class of two-dimensional layered materials consisting of alkali or coinage metal atoms sandwiched between slabs exclusively made of transition metal and chalcogen (or pnictogen) atoms arranged in a honeycomb fashion have emerged as materials exhibiting fascinatingly rich crystal chemistry, high-voltage electrochemistry, fast cation diffusion besides playing host to varied exotic electromagnetic and topological phenomena. Currently, with a niche application in energy storage as high-voltage materials, this class of honeycomb layered oxides serves as ideal pedagogical exemplars of the innumerable capabilities of nanomaterials drawing immense interest in multiple fields ranging from materials science, solid-state chemistry, electrochemistry and condensed matter physics. In this review, we delineate the relevant chemistry and physics of honeycomb layered oxides, and discuss their functionalities for tunable electrochemistry, superfast ionic conduction, electromagnetism and topology. Moreover, we elucidate the unexplored albeit vastly promising crystal chemistry space whilst outlining effective ways to identify regions within this compositional space, particularly where interesting electromagnetic and topological properties could be lurking within the aforementioned alkali and coinage-metal honeycomb layered oxide structures. We conclude by pointing towards possible future research directions, particularly the prospective realisation of Kitaev-Heisenberg-Dzyaloshinskii-Moriya interactions with single crystals and Floquet theory in closely-related honeycomb layered oxide materials. This journal i
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