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a¹H SSNMR spectra of the diamagnetic ammonioalunite, (NH4)Al3(SO4)2(OH)6 and b¹H SSNMR spectra of the diamagnetic hydronium gallium alunite, (D3O)Ga3(SO4)2(OH)6 with the different hydrogen species assigned Spectra recorded at 900 MHz. The asterisk indicates a negligible amount of an unknown impurity
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The various hydrogen species present in a series of synthetic hydroniumjarosite ((H3O)Fe3(SO4)2(OH)6), and ammonioalunite ((NH4)Al3(SO4)2(OH)6) as well synthetic potassium (Cr³⁺ and V³⁺) and hydronium (V³⁺, Cr³⁺, and Ga³⁺) analogues were identified and quantified by ¹H and ²H MAS NMR spectroscopy. The results confirm the defect mechanism proposed f...
Citations
... where values of n = 3, 2, or 0 corresponds to the A-site being fully occupied by D 3 O + , D 2 O, or K + respectively. The 2 H MAS NMR spectrum (Fig. 2) contains the spinning side band manifold for 4 resonances located at δ iso = 872(10), 828(5), 229(5), and 7(2) ppm, which are assigned to Cr 2 -OD (D), Cr 2 -OD (K), Cr -OD 2 and D n O, respectively, using earlier reported data [20,41]. The Cr 2 -OD resonances stem from stoichiometric Crjarosite with either D n O or K + on the A-site. ...
... Fig. 11 shows the PXRD diffractogram of the Cr-jarosite sample. This matches earlier reported diffractograms [20,41]. ...
The dynamics of the S = 3=2 kagome antiferromagnet chromium jarosite, KCr$_3$(OD)$_6$(SO$_4$)$_2$ was studied using high-resolution neutron time-of-flight spectroscopy on a polycrystalline sample with a nearly stoichiometric magnetic lattice (2.8(2)% Cr vacancies). Neutron spectroscopy reveals diffuse spin wave excitations in the ordered phase with an incomplete gap and significant finite life-time broadening as well as a pronounced zero mode. Using linear spin wave theory, we estimate the exchange couplings, with the leading nearest neighbor value being $J_1$ = 0:884 meV. Above $T_N$ diffuse excitations from cooperative paramagnetism dominate. A model for two-dimensional magnetic cluster excitations is shown to capture the essential features of the data in the cooperative paramagnetic phase.
... Our calculations carried out for isolated complexes give 7.3 and 4.6 (17.5) ppm for the isotropic chemical shift for free H 3 O + and H 5 O 2 + clusters, respectively (the number in parenthesis corresponds to the central proton). These calculations are supported by several experimental studies of hydrated layered oxides, in which the signal at 8-11 ppm was assigned to the H 3 O + [32,36,[44][45][46]. Hence, following both theoretical and experimental studies of other complex layered oxides, and accounting that for α-form of HCa 2 Nb 3 O 10 ·yH 2 O there are 1.6 H 2 O molecules and one interlayer proton per one formula, it can be suggested that one water molecule participates in the formation of H 3 O + , the signal L2 at about 7 ppm, whereas other signals correspond to water molecules that are localized in different sites of the charged interlayer space or are part of the more extended charged complexes, like H + . . . ...
The photocatalytic activity of layered perovskite-like oxides in water splitting reaction is dependent on the hydration level and species located in the interlayer slab: simple or complex cations as well as hydrogen-bonded or non-hydrogen-bonded H2O. To study proton localization and dynamics in the HCa2Nb3O10·yH2O photocatalyst with different hydration levels (hydrated-α-form, dehydrated-γ-form, and intermediate-β-form), complementary Nuclear Magnetic Resonance (NMR) techniques were applied. 1H Magic Angle Spinning NMR evidences the presence of different proton containing species in the interlayer slab depending on the hydration level. For α-form, HCa2Nb3O10·1.6H2O, 1H MAS NMR spectra reveal H3O+. Its molecular motion parameters were determined from 1H spin-lattice relaxation time in the rotating frame (T1ρ) using the Kohlrausch-Williams-Watts (KWW) correlation function with stretching exponent β = 0.28: Ea=0.2102 eV, τ0=9.01 × 10-12 s. For the β-form, HCa2Nb3O10·0.8H2O, the only 1H NMR line is the result of an exchange between lattice and non-hydrogen-bonded water protons. T1ρ(1/T) indicates the presence of two characteristic points (224 and 176 K), at which proton dynamics change. The γ-form, HCa2Nb3O10·0.1H2O, contains bulk water and interlayer H+ in regular sites. 1H NMR spectra suggest two inequivalent cation positions. The parameters of the proton motion, found within the KWW model, are as follows: Ea=0.2178 eV, τ0=8.29 × 10-10 s.
... 2 H MAS NMR of synthetic samples established the defect mechanism and local magnetic properties, thereby resolving the ambiguity about the existence of hydronium (H 3 O þ ) in these minerals [123]. The presence of solid acids (H 3 O þ and H 2 O 5 þ ions) in iron sulfates such as hydronium jarosite and rhomboclase has been proven by 2 H MAS NMR [123][124][125]. Many important binding sites for contaminants are often ill-defined mineral phases such as ferrihydrite and basaluminite, where SSNMR provides key information about the local environment and their relative concentrations. ...
Environmental science is an interdisciplinary field, which integrates chemical, physical, and biological sciences to study environmental problems and human impact on the environment. This article highlights the use of solid-state NMR spectroscopy (SSNMR) in studies of environmental processes and remediation with examples from both laboratory studies and samples collected in the field. The contemporary topics presented include soil chemistry, environmental remediation (e.g., heavy metals and radionuclides removal, carbon dioxide mineralization), and phosphorus recovery. SSNMR is a powerful technique, which provides atomic-level information about speciation in complex environmental samples as well as the interactions between pollutants and minerals/organic matter on different environmental interfaces. The challenges in the application of SSNMR in environmental science (e.g., measurement of paramagnetic nuclei and low-gamma nuclei) are also discussed, and perspectives are provided for the future research efforts.
... This explains the partial occupancy of alkali ions on the A-site, as confirmed by solid state NMR spectroscopy. [29][30][31] The presence of both M and A-site vacancies is closely linked to the synthesis method of choice. 19,25,[29][30][31] The preparation of stoichiometric Cr jarosites is difficult and requires a slow, controlled release of Cr 3+ by oxidation of elemental chromium. ...
... [29][30][31] The presence of both M and A-site vacancies is closely linked to the synthesis method of choice. 19,25,[29][30][31] The preparation of stoichiometric Cr jarosites is difficult and requires a slow, controlled release of Cr 3+ by oxidation of elemental chromium. 12 To our knowledge, neutron diffraction has been reported on Cr-jarosite samples from four different synthesis approaches, but crucial experimental details about the synthesis procedure and sample composition, including Cr concentration, are missing in most studies. ...
... Earlier reported 2 H NMR data were used as starting parameters. 31 We note that the main contribution to ∆ is from the paramagnetic dipolar interaction as 2 H in inorganic materials has negligible chemical shift anisotropy (≤ 10 ppm). The quadrupole interaction is reported as the nuclear quadrupole coupling constant, ...
Potassium chromium jarosite, KCr 3 (OH) 6 (SO 4) 2 (Cr-jarosite), is considered a promising candidate to display spin liquid behavior due to the strong magnetic frustration imposed by the crystal structure. However, the ground state magnetic properties have been debated, since Cr-jarosite is notoriously non-stoichiometric. Our study reports the magnetic properties for deuterated KCr 3 (OD) 6 (SO 4) 2 on chemically well-defined samples, which have been obtained by a combination of powder X-ray diffraction, neutron diffraction, solid state NMR spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy. Eight polycrystalline samples, which all only contained 1-3% Cr vacancies were obtained. However, significant substitution (2-27%) of potassium with H 2 O and/or H 3 O + was observed and resulted in pronounced stacking disorder along the c-axis. A clear second-order transition to an antiferromagnetically ordered phase at T N = 3.8(1) K with a small net moment, 0.03 µ B , per Cr 3+-ion was obtained from vibrating sample magnetometry and temperature dependent neutron diffraction. The moment is attributed to spin canting caused by the Dzyaloshinskii-Moriya interaction. Thus, our experimental results imply that even ideal potassium chromium jarosite will exhibit magnetic order below 4 K and therefore it does not qualify as a true spin liquid material.
The dynamics of the S=3/2 kagomé antiferromagnet chromium jarosite, KCr3(OD)6(SO4)2, was studied using high-resolution neutron time-of-flight spectroscopy on a polycrystalline sample with a nearly stoichiometric magnetic lattice [2.8(2)% Cr vacancies]. Neutron spectroscopy reveals diffuse spin wave excitations in the ordered phase with an incomplete gap and significant finite-lifetime broadening as well as a pronounced kagomé zero mode. Using linear spin wave theory, we estimate the exchange couplings. The system is highly two dimensional with the leading nearest-neighbor coupling being J1=0.881 meV. Above TN, diffuse excitations from the classical spin liquid regime dominate. We model the Q response and energy response separately and show that in both the ordered phase and the classical spin liquid regime they are strongly coupled.
This solid-state NMR report summarises the subject and results of 247 articles and original papers published in 2019. In addition to the published reviews, the two major sections in this report consider various methodological developments and a broad range of applications. The presented classification of papers into different sections and subsections is intended to ease the overview of the results obtained in 2019, as well as to evaluate the directions in which solid-state NMR is likely to develop in the near future.
