Acid-Base Centers and Acid-Base Scales in Ionic Solids

Abstract

For the case of ionic crystals it is shown to be most straightforward and consistent to define acidity/basicity by the (electro-)chemical potential of the respective ion, in a similar fashion to the way that the Fermi level (i.e.. electrochemical potential of the electron) characterizes the redox state. The isomorphy is explicitly expressed by using the energy-level diagrams introduced for electrons in semiconductor physics. Without having to make further assumptions it is possible 1) to compare acidity/basicity between different solids, 2) to link internal and surface acidity/basicity, and 3) to establish acidity/basicity scales for ionic solids. The point defects are revealed to be the natural acidic and basic elementary centers, and associates between them to be the internal acids/bases exchanging these elementary centers. Even though acidity/basicity is an overall property of the solid, the number of point defects (if dilute) directly represents these properties in the same way as H+ or OH- accomplish this for aqueous solutions.

Ionics versus electronics, and the general case of mixed conductor

“…In the case of the oxide higher-lying interstitial levels may also exist but occur as discrete structures (see text). For details the reader is referred to [9] from which the figure is taken. and time.…”

“…on a logarithmic scale. In the case of water this is obviously pH and pOH and in the case of ionic defects in ionic solids one obviously arrives at analogous acid-base scales [9]. The fact that two types of internal reactions dominate solid state chemistry, namely redox-reactions which involve electron transfer and acidbase reactions which involve ion transfer, directly reflects the analogous but also complementary role of electronic and ionic defects.…”

“…Again, this is analogous to H 2 O: Acetic acid, e. g. the "associate" of the impurity acetate (OAc − ) with H + is a proton generator in aqueous solutions. For details the reader is referred to [9].…”

Doping Strategies in Inorganic and Organic Materials

“…The analogous situation with strong and weak acids and bases was worked out in Ref. [14] and straightforwardly leads to a precise acid base concept for ionic crystalline solids.…”

Spark Plasma Sintering and Hot Pressing of Hetero‐Doped LaNbO4

“…This will influence the chemical potential gradient across the heterophase interfaces. 23 In this work, the sintering behavior, microstructure, and electrical properties of these composite materials are investigated to elucidate the possibility of developing hetero-doped LaNbO 4 . 24 To prevent precipitation, the pH was adjusted with ammonium hydroxide NH 4 OH (25%) and HNO 3 (65%) (both Merck).…”