Alkali-ion concentration dependence of the structure of proton-conducting alkali thio-hydroxogermanates investigated with neutron diffraction
Artikel i vetenskaplig tidskrift, 2015

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.

Proton conducting

Neutron diffraction

Thio-hydroxogermanate

Fuel cell

Författare

Maths Karlsson

Chalmers, Teknisk fysik, Kondenserade materiens fysik

Jonas Nordström

Chalmers, Teknisk fysik, Kondenserade materiens fysik

Aleksandar Matic

Chalmers, Teknisk fysik, Kondenserade materiens fysik

Steve Martin

Iowa State University

S. Imberti

ISIS Facility

D.T. Bowron

ISIS Facility

Solid State Ionics

0167-2738 (ISSN)

Vol. 274 40-45

Ämneskategorier

Fysikalisk kemi

DOI

10.1016/j.ssi.2015.02.019

Mer information

Skapat

2017-10-07