| 1. |
- Hall, Andreas, 1975, et al.
(författare)
-
Structure of Ag x Na 1−x PO 3 glasses by neutron diffraction and reverse Monte Carlo modelling
- 2007
-
Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:41
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed structural studies of mixed mobile ion phosphate glasses Ag x Na 1−x PO 3 using diffraction experiments and reverse Monte Carlo simulations. This glass system is particularly interesting as a model system for investigations of the mixed mobile ion effect, due to its anomalously low magnitude in the system. As for previously studied mixed alkali phosphate glasses, with a much more pronounced mixed mobile ion effect, we find no substantial structural alterations of the phosphorous–oxygen network and the local coordination of the mobile cations. Furthermore, the mobile Ag + and Na + ions are randomly mixed with no detectable preference for either similar or dissimilar pairs of cations. However, in contrast to mixed mobile ion systems with a very pronounced mixed mobile ion effect, the two types of mobile ions have, in this case, very similar local environments. For all the studied glass compositions the average Ag–O and Na–O distances in the first coordination shell are determined to be 2.5 ± 0.1 and 2.5 ± 0.1 Å, and the corresponding average coordination numbers are approximately 3.2 and 3.7, respectively. The similar local coordinations of the two types of mobile ions suggests that the energy mismatch for a Na + ion to occupy a site that previously has been occupied by a Ag + ion (and vice versa) is low, and that this low energy mismatch is responsible for the anomalously weak mixed mobile ion effect. (Some figures in this article are in colour only in the electronic version).
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Karlsson, Maths, 1978, et al.
(författare)
-
Alkali-ion concentration dependence of the structure of proton-conducting alkali thio-hydroxogermanates investigated with neutron diffraction
- 2015
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 274, s. 40-45
-
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.
|
|
| 6. |
|
|
| 7. |
- Karlsson, Maths, 1978, et al.
(författare)
-
Structure of Proton-Conducting Alkali Thio-Hydroxogermanates
- 2008
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 20:19, s. 6014-6021
-
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.
|
|
| 8. |
- Sillrén, Per, 1982, et al.
(författare)
-
The temperature dependent structure of liquid 1-propanol as studied by neutron diffraction and EPSR simulations
- 2013
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 138:21, s. 214501-
-
Tidskriftsartikel (refereegranskat)abstract
- The structure of liquid 1-propanol is investigated as a function of temperature using neutron diffrac- tion together with Empirical Potential Structure Refinement modelling. The combined diffraction and computer modelling analysis demonstrates that propanol molecules form hydrogen bonded clusters with a relatively wide size distribution, which broadens at lower temperatures. We find that the clus- ter size distribution is well described by a recently proposed statistical model for branched H-bonded networks [P. Sillrén, J. Bielecki, J. Mattsson, L. Börjesson, and A. Matic, J. Chem. Phys. 136, 094514 (2012)]. The average cluster size increases from ∼3 to 7 molecules, whilst the standard deviation of the size distribution increases from 3.3 to 8.5 as the temperature is decreased from 293 to 155 K. The clusters are slightly branched, with a higher degree of branching towards lower temperatures. An analysis of the cluster gyration tensor (Rmn) reveals an average elongated ellipsoidal shape with axes having proportions 1:1.4:1.9. We find that the average radius of gyration has a cluster size dependence consistent with that of fractal clusters, Rg ∝ n1/D , with a fractal dimension D ≈ 2.20, which is close to D = 2.00 expected for an ideal random walk or D = 2.11 expected for reaction limited aggregation. The characteristic angles between the H-bonded OH-groups that constitute the clusters show only a weak temperature dependence with O–H· · ·O angles becoming more narrowly distributed around 180◦ at lower temperatures.
|
|
