The Fermi energy as common parameter to describe charge compensation mechanisms: A path to Fermi level engineering of oxide electroceramics

Abstract

Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering.

Effect of iron acceptor doping and calcium donor doping in potassium sodium niobate‐based lead‐free piezoceramics

“…This is particularly relevant when cations possess multiple stable electronic configurations, as is the case with transition metal cations like Fe 3+ /Fe 4+ 84,85,86 . This means that the self‐trapping of holes results in polaron formation 87 . Polaron or trapping states have been identified in many iron‐doped perovskites, for example, Fe‐doped BT, 88 LiNbO 3 , 89 and SrTiO 3 materials 88 .…”

Investigation of O/N Ordering in Perovskite-Type Oxynitrides La1−xYxTa(O,N)3 on Long Range and Short Scale

“…For LaTaON 2 and La 0.9 Y 0.1 TaON 2 , within experimental uncertainty, the nominal compositions were confirmed by the refinements. It is important to note that the refinements of the La 0.9 Y 0.1 TaO 2 N compound revealed that the real composition was La 0.9 Y 0.1 TaO 1.58 (7) N 1.42 (7) . For LaTaO 2 N, the situation remained somewhat unclear as the free refinements strongly pointed to the presence of a N-rich composition.…”

“…Inorganics 2024, 12, 90 2 of 18 Consequently, a change in the Fermi level and defects in the crystal structure, such as oxygen vacancies, can come as an effect of the partial substitution of oxygen by nitrogen [7]. What results is a link between anionic doping-and hence the anionic ordering-and the electronic structure, which is highly important to understand.…”

“…The lowest values obtained by refinements based on physically meaningful parameters are highlighted in bold. N/A refers to the fact that since the real composition of the compound was La 0.9 Y 0.1 TaO 1.58(7) N 1.42(7) , the structural model was non-applicable.…”

Correlation Analysis in X-ray Photoemission Spectroscopy

“…Unlike metals, the Fermi level can be altered by several electronvolts in many semiconductors by relatively minor changes in the defect chemistry. [24][25][26] Fermi level shifts cause the measured binding energy of the core lines to shift by an equivalent energy.…”