Potassium stabilization in β-K2Fe22O34 by Cr and Ce doping studied by field reversal method

DIFFUSION, SEGREGATION AND DESORPTION OF POTASSIUM FROM K2Fe22O34 FERRITE

“…The former one being in a can be attributed to surface and grain boundary diffusion, as described for Mg-stabilized K + -β-ferrite. 21 Although similar value (0.53 eV) observed previously was assigned to an intersystem crossing (from surface covalent to ionic states of potassium), 16 in our case the value of 0.52 eV being determined from AC conductivity measurements indicates that this energy can rather be associated with the K + diffusion barrier in the K-β-ferrite phase. In the temperature range 700-800 K the ionic conductivity is the dominant process observed for K + dynamics in the interspinel block galleries.…”

“…2 indicates that in these conditions the surface coverage is relatively small and the accumulation of potassium at the surface is essentially not accompanied by a clustering process. Among three possible surface states of potassium (two covalent and one ionic) discussed in detailed elsewhere, 16,18 the linear dependence of work function changes as a function of coverage suggests that the predominant contribution comes from the surface K + -O surf dipoles associated with the ionic form.…”

Magnesium Effect in K/Co-Mg-Mn-Al Mixed Oxide Catalyst for Direct NO Decomposition

“…In paper [18], it was found that the addition of transition metal elements to the oxide lattice can inhibit the loss of potassium during diesel soot combustion and in [19], it was reported that introduction of alien metal ions, in specific cases, can substantially improve the stability of potassium ferrites. The principal location of potassium remained unchanged by the introduction of the dopants, while the type of stabilization depended on the distribution and placement of the dopants in the catalyst material [20]. Two ways of K desorption prevention were reported: (i) incorporation of the K promoter into the structure, which slows down potassium diffusion from the bulk towards the surface by steric hindrance, and (ii) locating the K promoter at the basal planes, favoring the cationic state of the potassium, which inhibits the probability of potassium atoms leaving the surface via work function increase [19,21].…”

First-Principles Determination of the K-Conductivity Pathways in KAlO2

“…Fast ion-conducting materials are indispensable for new-generation energy storage and power devices (supercapacitors and electrochemical and fuel cells). Among them, metal oxides with highly mobile Li + and Na + charge carriers, such as the lithium (LiSICON) and sodium (NaSICON) superionic conductors as well as olivine- and perovskite-type oxides, are frequently considered, but also compounds with larger cations (e.g., K + ) have gathered attention in recent years. − The description of the ion diffusion within a material is key for predicting its performance. In new compounds the ion-conducting pathways are not known and theoretical methods allowing us to predict them are rare. − In fact, the bulk of these approaches require assuming certain pathways and thus are limited to compounds of moderate complexity. − ,, In this respect, general methods capable of discerning the ion-conducting channels, such as molecular dynamics simulations, are of great practical importance.…”