Insight into the Local Magnetic Environments and Deuteron Mobility in Jarosite (AFe(3)(SO(4))(2)(OD,OD(2))(6), A = K, Na, D(3)O) and Hydronium Alunite ((D(3)O)Al(3)(SO(4))(2)(OD)(6)), from Variable-Temperature (2)H MAS NMR Spectroscopy

[摘要]：Detailed insight into the magnetic properties and mobility of the different deuteron species in jarosites (AFe(3)(SO(4))(2)(OD)(6), A = K, Na, D(3)O) is obtained from variable-temperature (2)H MAS NMR spectroscopy performed from 40 to 300 K. Fast MAS results in high-resolution spectra above the Neel transition temperature (i.e., in the paramagnetic regime). The (2)H NMR hyperfine shift (delta), measured as a function of temperature, is a very sensitive probe of the local magnetic environment. Two different magnetic environments are observed: (i) Fe(2)-OD groups and D(3)O(+) ions in stoichiometric regions of the sample. Here, the delta((2)H) values are proportional to the bulk susceptibility and follow a Curie-Weiss law above 150 K. (ii) Fe-OD(2) groups and D(2)O molecules located near the Fe(3+) vacancies in the structure. The Fe(3+) ions near these vacancies show strong local antiferromagnetic couplings even high above the Neel temperature (of ca. 65 K). The D(2)O and D(3)O(+) ions located on the jarosite A site can be distinguished in the (2)H NMR spectra due to the different temperature dependence of their isotropic shifts. Motion of the D(3)O(+) ions was followed by investigating the isostructural (diamagnetic) compound (D(3)O)Al(3)(SO(4))(2)(OD)(6) and an activation energy of 6.3(4) kJ/mol is determined for the D(3)O(+) motion. Our NMR results support theories that ascribe the spin glass behavior that is observed for (H(3)O)Fe(3)(SO(4))(2)(OD)(6) but not for the other cation substituted jarosites, to the disorder of the D(3)O(+) ions and/or a less distorted Fe coordination environment. No signs of proton transfer reactions from the D(3)O(+) ion to the framework are observed.

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