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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Controlling magnetic configuration in soft–hard bilayers probed by polarized neutron reflectometry

Hard/soft magnetic bilayer thin films have been widely used in data storage technologies and permanent magnet applications. The magnetic configuration and response to temperatures and magnetic fields in these heterostructures are considered to be highly dependent on the interfacial coupling. However, the intrinsic properties of each of the layers, such as the saturation magnetization and layer thickness, also strongly influence the magnetic configuration. Changing these parameters provides an effective method to tailor magnetic properties in composite magnets. Here, we use polarized neutron reflectometry (PNR) to experimentally probe the interfacial magnetic configurations in the hard/soft bilayer thin films: L1 0 -FePt/A1-FePt, [Co/Pd]/CoPd, [Co/Pt]/FeNi, and L1 0 -FePt/Fe, all of which have a perpendicular magnetic anisotropy in the hard layer. These films were designed with different soft and hard layer thicknesses (t soft and t hard ) and saturation magnetization (M$_s^{soft}$ and M$_s^{hard}$). The influences of an in-plane magnetic field (H ip ) and temperature (T) are also studied using a L1 0 -FePt/A1-FePt bilayer sample. Comparing the PNR results to the micromagnetic simulations reveals that the interfacial magnetic configuration is highly dependent on t soft , M$_s^{soft}, and the external factors (H ip and T) and has a relatively weak dependence on t hard and M$_s^{hard}$. Key among these results, for thin t soft , the hard and soft layers are rigidly coupled in the out-of-plane direction and then undergo a transition to relax in-plane. This transition can be delayed to larger t soft by decreasing M$_s^{soft}$. Understanding the influence of these parameters on the magnetic configuration is critical to designing functional composite magnets for applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Structural and magnetic properties of CoTeMo⁢O 6

Here, we have conducted a comprehensive investigation into the magnetic properties of the chiral multiferroic material CoTeMo⁢O 6 . In contrast with the previous claim of canted antiferromagnetic order with ferromagnetic components [Y. Doi et al., J. Solid State Chem. 182, 3232 (2009)], our investigation reveals an antiferromagnetic ground state with compensated moments, providing an interesting platform for exploring exotic material properties. Through careful measurements of magnetization under a series of applied fields, we demonstrate that there exist two sequential field-induced magnetic transitions in CoTeMo⁢O 6 , with one occurring at 𝐻 𝑐⁢1 =460 Oe along the 𝑎 axis, and the other at 𝐻 𝑐⁢2 =1.16 T with the field along the 𝑏 axis. The values of 𝐻 𝑐⁢1 and 𝐻 𝑐⁢2 exhibit strong angular dependence and diverge with different rates as the applied field is rotated 90 ° within the 𝑎⁢𝑏 plane. This reflects the distinct nature of these transitions, which is further supported by the different critical behavior of 𝐻 𝑐⁢1 and 𝐻 𝑐⁢2 , characterized by the values of 𝛾, in the function of 𝐻 𝑐 =𝐻 0 ⁡(1−𝑇/𝑇 𝑐 ) 𝛾 . Furthermore, we have demonstrated that there exist structural and magnetic twin domains in CoTeMo⁢O 6 that strongly affect the experimental measurement of their macroscopic properties. Intriguingly, these twin domains can be related to the orthorhombicity/chirality of the crystal structure with the space group 𝑃⁢2 1 ⁢2 1⁢ 2. We further explored the magnetic and structural domains with uniaxial pressure and polarized light microscopy. Our results suggest that CoTeMo⁢O 6 could be used as a unique platform for investigating the intriguing physics involving intertwined degrees of freedom. The tunability of the underlying domain distribution and its strong anisotropy could also be useful for developing functional devices and applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Angle-resolved polarized Raman study of layered b-As x P x-1 alloys: Identification of As-P vibrational modes

In this study, the polarization-resolved Raman spectra of b-As x P x-1 flakes with varying arsenic concentration (x = 0, 0.4, and 0.8) are systematically investigated. A clear polarization dependence is observed in the Raman intensity of all the P-P, As-P, and As-As modes and confirmed by the first-principles calculations. The observed angle-dependence can be related to the structure of the Raman tensors of each peak. In particular, the Raman intensities corresponding to As-P vibration modes are studied in detail. The out of plane As-P mode ($A$$^{1}_{g}$) is clearly identified, but the butterfly-shaped behavior observed in the polar plot around 350 cm -1 is interpreted as the combination of the two in-plane vibrations, one along the armchair and the other along the zigzag direction. This work allows unambiguous assignment of the $A$$^{1}_{g}$, B 2g , and $A$$^{2}_{g}$ modes of the As-P vibrational modes and the importance of the consideration of the superposition of the in-plane B 2g and $A$$^{2}_{g}$ modes. Such study can be utilized to further characterize the anisotropic structural properties and analyze the local distribution of the As and P in b-As x P x-1 alloys which will play key roles in electronic and optical properties. Furthermore, this methodology can be further extended to alloyed two-dimensional material systems with in-plane anisotropy in general.

2D materials↗
DOE OSTI2023

Impact of the chiral asymmetry and a magnetic field on the passage of an energetic test parton in a QCD medium

We study the dependence of soft contribution to the energy loss of a test parton moving with a high velocity on the chiral imbalance and magnetic field in the QCD medium. A semiclassical approach is adopted to estimate the parton energy loss that takes into account the back-reaction on the parton due to the polarization effects of the QCD medium while traversing through the medium. We find that the motion of the parton is sensitive to the chiral asymmetry in the medium. Further, we investigate the effect of magnetic field-induced anisotropy on the energy transfer between the moving parton and the medium. Our results show that the energy loss of the parton is strongly influenced by the strength of the magnetic field as well as the relative orientation of the motion of the parton and the direction of the magnetic field in the medium.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Highly Anisotropic Drude-Weight-Reduction and Enhanced Linear-Dichroism in van der Waals Weyl Semimetal T d -MoTe 2 with Coherent Interlayer Electronic Transport

Weyl semimetal (WSM) states can be achieved by breaking spatial-inversion symmetry or time reversal symmetry. However, the anisotropy of the energy reduction contributing to the emergence of WSM states has seldom been investigated by experiments. A van der Waals metal MoTe 2 exhibits a type-II WSM phase below the monoclinic-to-orthorhombic-phase-transition temperature T c ~ 250 K. Here, in this work, a combined linearly polarized optical-spectroscopy and electrical-transport study of MoTe 2 is reported at different temperatures. The Drude components in the a-axis, b-axis, and c-axis optical conductivity spectra, together with the metallic out-of-plane and in-plane electrical resistivities, indicate the coherent inter-layer and in-plane charge transports. Moreover, the Drude weight in σ 1a (ω), rather than the Drude weights in σ 1b (ω) and σ 1c (ω), decreases dramatically below T c , which exhibits a highly anisotropic decrease in its Drude weight and thus suggests a strongly anisotropic reduction of the electronic kinetic energy in the WSM phase. Furthermore, below T c , due to the in-plane anisotropic spectral-weight transfer from Drude component to high-energy region, the in-plane inter-band-absorption anisotropy increases remarkably ≈770 meV, and has the largest value (≈0.68) of normalized linear dichroism among the reported type-II WSMs. The work sheds light on seeking new WSMs and developing novel photonic devices based on WSMs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Electronic and magnetic properties of iridium-based novel Heusler alloys

We report half-metallicity and magnetism including exchange splitting are the most significant physical parameters to predict and design a candidate material for spintronic applications. We report here an ab-initio investigation on chemical formation and dynamical stability along with electronic structure and magnetic properties of Ir 2 Cr (Si, Ge) and IrRhCr (Si, Ge) Heusler alloys. The negative formation and cohesive energies with positive phonon dispersions confirm the stabilities of these alloys. Electronic structure calculations reveal that Ir 2 Cr (Si, Ge) and IrRhCrSi alloys are half-metallic ferromagnets with unprecedented exchange splitting. In addition, IrRhCrGe also shows semi-metallic nature. All of these materials follow Slater Pauling rule with large magnetic moments and 100% spin-polarization. With Cr bearing the majority of the local magnetic moment and exchange splitting, a ferromagnetic state is more stable than a nonmagnetic state. The electronic charge distribution and population analysis confirm mixed ionic and covalent bonding. The magnetocrystalline anisotropy energy, with the easy magnetization along the [1 1 1] direction, is significantly high in Ir 2 CrGe. Elastic constants such as shear (G), bulk (B), Young’s moduli, and Poisson’s ratio indicate that the IrRhCrSi and IrRhCrGe alloys are mechanically stable, and Ir 2 CrSi and Ir 2 CrGe are mechanically unstable. The Pugh’s (B/G) and Poisson’s ratios confirm that the stable alloys are ductile.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Pairing around a single Dirac point: A unifying view of Kohn-Luttinger superconductivity in Chern bands, quarter metals, and topological surface states

Superconductivity of a single two-dimensional Dirac fermion offers a natural route to topological superconductivity. While usually considered extrinsic—arising from proximity to a conventional superconductor—we investigate when a doped Dirac cone can develop superconductivity from a short-range repulsive interaction 𝑈 via the Kohn–Luttinger mechanism. We show that an ideal, linear Dirac cone is immune to pairing at leading order in 𝑈 2 . Superconductivity instead emerges only through higher-order in 𝑘 corrections to the dispersion, which are unavoidable in any lattice realization and crucially dictate the pairing symmetry. The form of the pairing thus reflects how the well-known obstruction to realizing a single Dirac cone on a lattice is circumvented. When a Dirac cone arises from broken time-reversal symmetry—for instance, at a transition between Chern insulators or in a valley-polarized phase—we find a topological 𝑝−𝑖⁢𝑝 state whose chirality is opposite to that of the parent chiral metal above 𝑇 𝑐 . By contrast, for a surface Dirac cone of a 3D topological insulator, superconductivity is stabilized by anisotropies in the dispersion. For 𝐶 3⁢𝑣 -symmetric warping, as in , pairing is strongest when the Fermi surface becomes hexagonal, leading to order in the (𝑑±𝑖⁢𝑑)×(𝑝+𝑖⁢𝑝) channel with accidental near-nodes. In the highly anisotropic limit 𝑣 𝑥 ≫𝑣 𝑦 , relevant to side surfaces of layered materials, the Fermi surface splits into two branches, and nesting favors a pairing symmetry 𝛥∼s⁢g⁡n⁢(𝑘 𝑥 )⁢cos⁡(𝑘 𝑦 ) reminiscent of organic superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Dark and Bright Excitons in Halide Perovskite Nanoplatelets

Semiconductor nanoplatelets (NPLs), with their large exciton binding energy, narrow photoluminescence (PL), and absence of dielectric screening for photons emitted normal to the NPL surface, could be expected to become the fastest luminophores amongst all colloidal nanostructures. However, super-fast emission is suppressed by a dark (optically passive) exciton ground state, substantially split from a higher-lying bright (optically active) state. Here, the exciton fine structure in 2-8 monolayer (ML) thick Cs n - 1 Pb n Br 3n + 1 NPLs is revealed by merging temperature-resolved PL spectra and time-resolved PL decay with an effective mass model taking quantum confinement and dielectric confinement anisotropy into account. This approach exposes a thickness-dependent bright-dark exciton splitting reaching 32.3 meV for the 2 ML NPLs. The model also reveals a 5-16 meV splitting of the bright exciton states with transition dipoles polarized parallel and perpendicular to the NPL surfaces, the order of which is reversed for the thinnest NPLs, as confirmed by TR-PL measurements. Accordingly, the individual bright states must be taken into account, while the dark exciton state strongly affects the optical properties of the thinnest NPLs even at room temperature. Significantly, the derived model can be generalized for any isotropically or anisotropically confined nanostructure.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Lattice flexibility in Ca 3 Ru 2 O 7 : Control of electrical transport via anisotropic magnetostriction

We report that Ca 3 Ru 2 O 7 is a correlated and spin-orbit coupled system with an extraordinary anisotropy. It is both interesting and unique largely because this material exhibits conflicting phenomena that are often utterly inconsistent with traditional precedents, particularly, the quantum oscillations in the nonmetallic state and colossal magnetoresistivity achieved by avoiding a fully spin-polarized state. This work focuses on the relationship between the lattice and transport properties along each crystalline axis and reveals that application of magnetic field, H, along different crystalline axes readily stretches or shrinks the lattice in a uniaxial manner, resulting in distinct electronic states. Furthermore, application of modest pressure drastically amplifies the anisotropic magnetoelastic effect, leading to either an occurrence of a robust metallic state at H $∥$ hard axis or a reentrance of the nonmetallic state at H $∥$ easy axis. Ca3Ru2O7 presents a rare lattice-dependent magnetotransport mechanism, in which the extraordinary lattice flexibility enables an exquisite control of the electronic state via magnetically stretching or shrinking the crystalline axes, and the spin polarization plays an unconventional role unfavorable for maximizing conductivity. At the heart of the intriguing physics is the anisotropic magnetostriction that leads to exotic states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Yet Another Sunshine Mystery: Unexpected Asymmetry in GeV Emission from the Solar Disk

The Sun is one of the most luminous γ-ray sources in the sky and continues to challenge our understanding of its high-energy emission mechanisms. This study provides an in-depth investigation of the solar disk γ-ray emission, using data from the Fermi Large Area Telescope spanning 2008 August to 2022 January. We focus on γ-ray events with energies exceeding 5 GeV, originating from 0°5 angular aperture centered on the Sun, and implement stringent time cuts to minimize potential sample contaminants. We use a helioprojection method to resolve the γ-ray events relative to the solar rotation axes and combine statistical tests to investigate the distribution of events over the solar disk. We found that integrating observations over large time windows may overlook relevant asymmetrical features, which we reveal in this work through a refined time-dependent morphological analysis. We describe significant anisotropic trends and confirm compelling evidence of energy-dependent asymmetry in the solar disk γ-ray emission. Intriguingly, the asymmetric signature coincides with the Sun's polar field flip during the cycle 24 solar maximum, around 2014 June. Our findings suggest that the Sun's magnetic configuration plays a significant role in shaping the resulting γ-ray signature, highlighting a potential link between the observed anisotropies, solar cycle, and the solar magnetic fields. These insights pose substantial challenges to established emission models, prompting fresh perspectives on high-energy solar astrophysics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Switching the spin cycloid in BiFeO3 with an electric field

Abstract Bismuth ferrite (BiFeO 3 ) is a multiferroic material that exhibits both ferroelectricity and canted antiferromagnetism at room temperature, making it a unique candidate in the development of electric-field controllable magnetic devices. The magnetic moments in BiFeO 3 are arranged into a spin cycloid, resulting in unique magnetic properties which are tied to the ferroelectric order. Previous understanding of this coupling has relied on average, mesoscale measurements. Using nitrogen vacancy-based diamond magnetometry, we observe the magnetic spin cycloid structure of BiFeO 3 in real space. This structure is magnetoelectrically coupled through symmetry to the ferroelectric polarization and this relationship is maintained through electric field switching. Through a combination of in-plane and out-of-plane electrical switching, coupled with ab initio studies, we have discovered that the epitaxy from the substrate imposes a magnetoelastic anisotropy on the spin cycloid, which establishes preferred cycloid propagation directions. The energy landscape of the cycloid is shaped by both the ferroelectric degree of freedom and strain-induced anisotropy, restricting the spin spiral propagation vector to changes to specific switching events.

36 MATERIALS SCIENCE↗
DOE OSTI2025

A magnon band analysis of GdRu 2 Si 2 in the field-polarized state

Understanding the formation of skyrmions in centrosymmetric materials is a problem of fundamental and technological interest. GdRu 2 Si 2 is a candidate material that hosts a variety of multi-Q magnetic phases, including in zero-field. Here, inelastic neutron scattering is used to measure the spin excitations in the field-polarized phase of GdRu 2 Si 2 . Linear spin wave theory and a method of interaction invariant path analysis are used to derive a Hamiltonian accounting for the spectra. The Hamiltonian, dominated by bilinear (Ruderman-Kittel-Kasuya-Yosida) Heisenberg exchange, compares favorably to ab initio calculations. Dipolar interactions are a secondary energy scale to consider, with J D.D ~ 0.05 J RKKY . However, it is shown that in the field-polarized phase the dipolar interactions ‘self screen’ so that their effect is largely suppressed. No specific evidence for higher-order exchange is found. These aspects are discussed in the context of the lower field multi-Q states and the anisotropy of the system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Anisotropic 2D excitons unveiled in organic-inorganic quantum wells

Here we report that two-dimensional (2D) excitons arise from electron-hole confinement along one spatial dimension. Such excitations are often described in terms of Frenkel or Wannier limits according to the degree of exciton spatial localization and the surrounding dielectric environment. In hybrid material systems, such as the 2D perovskites, the complex underlying interactions lead to excitons of an intermediate nature, whose description lies somewhere between the two limits, and a better physical description is needed. Here, we explore the photophysics of a tuneable materials platform where covalently bonded metal-chalcogenide layers are spaced by organic ligands that provide confinement barriers for charge carriers in the inorganic layer. We consider self-assembled, layered bulk silver benzeneselenolate, [AgSePh] ∞ , and use a combination of transient absorption spectroscopy and ab initio GW plus Bethe-Salpeter equation calculations. We demonstrate that in this non-polar dielectric environment, strongly anisotropic excitons dominate the optical transitions of [AgSePh] ∞ . We find that the transient absorption measurements at room temperature can be understood in terms of low-lying excitons confined to the AgSe planes with in-plane anisotropy, featuring anisotropic absorption and emission. Finally, we present a pathway to control the exciton behaviour by changing the chalcogen in the material lattice. Our studies unveil unexpected excitonic anisotropies in an unexplored class of tuneable, yet air-stable, hybrid quantum wells, offering design principles for the engineering of an ordered, yet complex dielectric environment and its effect on the excitonic phenomena in such emerging materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Out-of-plane polarization and topological magnetic vortices in multiferroic CrPSe 3

Two-dimensional multiferroic materials are ideal systems for exploring new coupling mechanisms between different ferroic orders and producing novel quantum phenomena with potential applications. Here we employ first-principles density functional theory calculations to discover intrinsic ferroelectric and antiferroelectric phases of Cr⁢P⁢Se 3 , which show ferromagnetic order and compete with the centrosymmetric phase with an antiferromagnetic order. Our analysis shows that the electrical dipoles of such type-I multiferroic phases come from the out-of-plane displacements of phosphorus ions due to the stereochemically active lone pairs. The coupling between polar and magnetic orders creates the opportunity for tuning the magnetic ground state by switching from the centrosymmetric to the ferroelectric phase using an out-of-plane electric field. In ferroelectric and antiferroelectric phases, the combination of easy-plane anisotropy and Dzyaloshinskii-Moriya interactions indicates that they can host topological magnetic vortices such as meron pairs.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Solid-phase heteroepitaxy of oriented Sb 2 Se 3 on GaAs for birefringent thin films

Here, we investigate the amorphous-to-crystalline transformation of antimony selenide (Sb 2 Se 3 ) on UHV-prepared GaAs (001) substrates. In the bulk orthorhombic form, Sb 2 Se 3 is a layered quasi-1D semiconductor with highly anisotropic properties of interest for optical and electronic devices. We find that an amorphous layer deposited by molecular beam epitaxy annealed at or above 230 °C yields a textured-epitaxial structure among some randomly oriented domains. The textured-epitaxial Sb 2 Se 3 grains are oriented with the covalently bonded “1D axis” constrained in-plane to GaAs [110] and with multiple van der Waals (hk0) orientations out-of-plane. The same texture was achieved exclusively without randomly oriented grains using continuous-wave laser radiation, highlighting the use of thermal and optical methods to yield anisotropic crystalline Sb 2 Se 3 films directly from the amorphous phase. Polarized reflectance and polarized microscopy confirm the unique state of in-plane birefringence in the crystallized thin film. Overall, we show that solid-phase heteroepitaxy provides additional pathways to the integration of low-symmetry chalcogenide semiconductors for demanding applications where the inherent anisotropy needs to be preserved.

Xiao, Kelly [Stanford Univ., CA (United States)] (↗
DOE OSTI2021

Spin-orbit–coupled exciton-polariton condensates in lead halide perovskites

Spin-orbit coupling (SOC) is responsible for a range of spintronic and topological processes in condensed matter. Here, we show photonic analogs of SOCs in exciton-polaritons and their condensates in microcavities composed of birefringent lead halide perovskite single crystals. The presence of crystalline anisotropy coupled with splitting in the optical cavity of the transverse electric and transverse magnetic modes gives rise to a non-Abelian gauge field, which can be described by the Rashba-Dresselhaus Hamiltonian near the degenerate points of the two polarization modes. With increasing density, the exciton-polaritons with pseudospin textures undergo phase transitions to competing condensates with orthogonal polarizations. Unlike their pure photonic counterparts, these exciton-polaritons and condensates inherit nonlinearity from their excitonic components and may serve as quantum simulators of many-body SOC processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The Atacama Cosmology Telescope: a measurement of the Cosmic Microwave Background power spectra at 98 and 150 GHz

We present the temperature and polarization angular power spectra of the CMB measured by the Atacama Cosmology Telescope (ACT) from 5400 deg2 of the 2013–2016 survey, which covers >15000 deg2 at 98 and 150 GHz. For this analysis we adopt a blinding strategy to help avoid confirmation bias and, related to this, show numerous checks for systematic error done before unblinding. Using the likelihood for the cosmological analysis we constrain secondary sources of anisotropy and foreground emission, and derive a “CMB-only” spectrum that extends to ℓ=4000. At large angular scales, foreground emission at 150 GHz is ∼1% of TT and EE within our selected regions and consistent with that found by Planck. Using the same likelihood, we obtain the cosmological parameters for ΛCDM for the ACT data alone with a prior on the optical depth of τ=0.065±0.015. ΛCDM is a good fit. The best-fit model has a reduced χ2 of 1.07 (PTE=0.07) with H0=67.9±1.5 km/s/Mpc. We show that the lensing BB signal is consistent with ΛCDM and limit the celestial EB polarization angle to ψP =−0.07ˆ±0.09ˆ. We directly cross correlate ACT with Planck and observe generally good agreement but with some discrepancies in TE. All data on which this analysis is based will be publicly released.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Structural characterization of tin in toothpaste by dynamic nuclear polarization enhanced 119 Sn solid-state NMR spectroscopy

Stannous fluoride (SnF 2 ) is an effective fluoride source and antimicrobial agent that is widely used in commercial toothpaste formulations. The antimicrobial activity of SnF 2 is partly attributed to the presence of Sn(II) ions. However, it is challenging to directly determine the Sn speciation and oxidation state within commercially available toothpaste products due to the low weight loading of SnF 2 (0.454 wt% SnF 2 , 0.34 wt% Sn) and the amorphous, semi-solid nature of the toothpaste. Here, we show that dynamic nuclear polarization (DNP) enables 119 Sn solid-state NMR experiments that can probe the Sn speciation within commercially available toothpaste. Solid-state NMR experiments on SnF 2 and SnF 4 show that 19 F isotropic chemical shift and 119 Sn chemical shift anisotropy (CSA) are highly sensitive to the Sn oxidation state. DNP-enhanced 119 Sn magic-angle turning (MAT) 2D NMR spectra of toothpastes resolve Sn(II) and Sn(IV) by their 119 Sn chemical shift tensor parameters. Fits of DNP-enhanced 1D 1 H → 119 Sn solid-state NMR spectra allow the populations of Sn(II) and Sn(IV) within the toothpastes to be estimated. This analysis reveals that three of the four commercially available toothpastes contained at least 80% Sn(II), whereas one of the toothpaste contained a significantly higher amount of Sn(IV).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗