Impact of angle and bond distance variation on the transport properties of perovskites

Abstract

Relations between the electrical conductivity responses, the direct and indirect cation interactions, the Cation-Anion bond distances, and the Cation-Anion-Cation angles are discussed. It is shown that both Cation-Cation and Cation-Anion-Cation interactions govern essentially the dynamics of the charge carriers in various oxide compounds. The electrical transport properties for materials containing transition metal cations are directly related to the Cation-Cation/Cation-Anion bond distances and Cation-Anion-Cation (α) angle values. Accordingly, for α > 135° and for weak Cation-Anion length, strong Cation-Anion-Cation interactions are observed, thus implying the appearance of a semiconductor behavior. Explicitly, for elevated Cation-Anion-Cation angle (α around 180°), no Cation-Cation interaction can be seen, which supports the development of materials with a semiconductor behavior. In this work, the temperature dependence of the electrical conductivity is considered to estimate the relative magnitudes of the Mn - Mn versus Mn-O-Mn interactions. Accordingly, for manganites with strong Mn - Mn interactions, covalent-type bonds may be formed at low temperatures. The appearance of metallic behavior within the mentioned material family is linked to the improvement of the Mn - Mn interactions degree. For various oxide systems, covalent-type Cation-Cation bond formation improves the phase transition from the metallic to the semiconductor behaviors, which can be cooperative or non-cooperative. The cooperative transition is observed at a definite temperature value. While, the non-cooperative transition can be noticeable over a finite temperature domain.