| 1. |
- Karlsson, Maths, 1978, et al.
(författare)
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Alkali-ion concentration dependence of the structure of proton-conducting alkali thio-hydroxogermanates investigated with neutron diffraction
- 2015
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 274, s. 40-45
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Tidskriftsartikel (refereegranskat)abstract
- The proton-conducting hydrated alkali thio-hydroxogermanate's MxGeSx(OH)(4) - x center dot yH(2)O (M = Na and K; x = 1 - 4,y approximate to 0.5 - 2) were investigated by means of neutron diffraction with the aim to elucidate how the structure changes as a function of alkali-ion concentration, x, type of alkali ion, M, and water content, y. For x = 1 - 3 we find that the materials are amorphous and composed of thio-hydroxogermanate anions, water molecules, and charge balancing alkali ions, whereas for x = 4 we find that the materials contain also a crystalline phase, suggesting that it is difficult to prepare purely amorphous materials for the highest alkali-ion concentration, for both the Na and K based materials. For x = 1 - 3, the structure is reflected by an intermediate-range ordering, with a characteristic length-scale ranging from approximately 6 to 9 angstrom, which is dependent on both x and M and which may be related to the separation distance between dimers of thio-hydroxogermanate anions. As x increases, the intermediate-range ordering shortens, possibly as the result of an increasing level of hydration water that may act as a dielectric medium that reduces the repulsive interaction between the negatively charged thio-hydroxogermanate anions and/or between the positively charged alkali ions. A comparison of the structural results to the reported conductivities of the same materials indicates a non-trivial relationship, which depends on both the type and concentration of alkali ions, as well as on the level of hydration water.
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| 2. |
- Karlsson, Maths, 1978, et al.
(författare)
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Structural Origin of the Mixed Glass Former Effect in Sodium Borophosphate Glasses Investigated with Neutron Diffraction and Reverse Monte Carlo Modeling
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:49, s. 27275-27284
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Tidskriftsartikel (refereegranskat)abstract
- The mixed glass former systems 0.35Na(2)O + 0.65[xB(2)O(3) + (1 - x)P2O5] and 0.5Na(2)O + 0.5[xB(2)O(3) + (1 - x)P2O5] with x = 0-1 were investigated with neutron diffraction (ND) together with reverse Monte Carlo (RMC) modeling of 0.35Na(2)O + 0.65[xB(2)O(3) + (1 - x)P2O5]. The results show that the structure of both systems is reflected by an intermediate-range ordering, with a characteristic x-dependent length scale of about 4-6 angstrom and which contracts slightly with the increase of the Na concentration. Results obtained from RMC modeling of the 0.35Na(2)O + 0.65[xB(2)O(3) + (1 - x)P2O5] system, using both previously reported X-ray diffraction (XRD) data as well as the here obtained ND data as independent constraints in the modeling, show that the intermediate-range structural features, notably the Na coordination and volume fraction of the conducting pathways, are only weakly dependent on the choice of the constraints used. In particular, we observe that the volume fraction of the conducting pathways and the activation energy for ionic conduction are only weakly correlated to each other, as opposed to what is found for binary alkali borate and phosphate glasses.
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| 3. |
- Karlsson, Maths, 1978, et al.
(författare)
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Structure of Proton-Conducting Alkali Thio-Hydroxogermanates
- 2008
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 20:19, s. 6014-6021
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Tidskriftsartikel (refereegranskat)abstract
- Using a combination of neutron diffraction, infrared spectroscopy, and first-principles calculations, we have investigated the structure of hydrated and dehydrated proton conducting alkali thio-hydroxogermanates of general formula M2GeS2(OH)2·yH2O (M = K, Rb, and Cs). The results show that the structure of hydrated and dry materials are basically the same, which confirms previous indications that the main effect of heating these materials is just a loss of water. We suggest that in the hydrated state the structure of these materials is built of dimers of thio-hydroxogermanate anions, with the water molecules acting as bridges between such dimers. In the dehydrated structure, the thio-hydroxogermanate anions instead form an extended network through the formation of interdimer hydrogen bonds through the −OH groups in the structure. The alkali ions are suggested to act as “space-fillers” in voids formed by the thio-hydroxogermanate anion dimers, in both the hydrated and the dehydrated state.
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| 4. |
- Shastri, Ananda, et al.
(författare)
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1H NMR study of the hydrogen dynamics in the (NaS)xGe(OH)4-x*y H2O ceramic proton conductors
- 2012
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 228, s. 46-55
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Tidskriftsartikel (refereegranskat)abstract
- 1H NMR was performed on the ceramic proton conductor (NaS)xGe(OH)4-x*y H2O for x=2,3 and y≈1-4 over the temperature range of −100 °C to 400 °C. NMR spectra, nuclear spin-lattice relaxation rates (R1), spin-spin relaxation rates (R2), and rotating frame relaxation rates (R1ρ) were obtained for both hydrated and dehydrated samples. It was found that the low temperature NMR spectra were consistent with simulated H2O lineshapes, and the presence of H3O+ at low temperature was not detected within the experimental uncertainty. Short- and long-range hydrogen motion occurred together, a signature of Grotthuss conduction mechanisms. The long range motion was a combination of H+ and H2O diffusion, with H2O motion limiting H+ dynamics as the onset temperature was approached.
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