Investigations of Proton Conduction in the Monoclinic Phase of RbH<sub>2</sub>PO<sub>4</sub> Using Multinuclear Solid-State NMR
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Bibliographic record
Abstract
To understand the nature of the high-temperature phase transition and the origin of proton conductivity in rubidium dihydrogen phosphate RbH 2 PO 4, (RDP), we utilized variable-temperature 1 H, 31 P, and 87 Rb MAS NMR at 11.7 and 21.1 T. The variable-temperature 1 H MAS NMR spectra do not show water peaks in the temperature range of 300−400 K, which argues against a partial polymerization and/or decomposition. The 1 H DQ MAS NMR spectra acquired at high field (21.1 T) reveal three different proton sites, and dipolar recoupling experiments give estimates of distances. This evidence supports the formation of a superstructure (doubling of the unit cell along the a -axis) in the high-temperature monoclinic phase. The variable-temperature proton spin−lattice relaxation ( T 1 ) reveals significant proton dynamics above 340 K, coinciding with the temperature at which an increase of bulk proton conductivity is reported in monoclinic RDP, but well below the macroscopic phase transition. These precursor dynamics foreshadow the onset of superprotonic conductivity. From variable- temperature 31 P and 87 Rb MAS NMR spectra, it is deduced that significant proton dynamics above 340 K are due to the proton transfer between hydrogen bonds accompanied by reorientation of PO 4 tetrahedra.
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Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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