Abstract
Electronic states of ions in lead-free perovskite-type dielectric oxides have been investigated with a first-principle cluster calculation. For this calculation a double-perovskite cluster model based upon the simple cubic ABO3 was used; A and B are both the cations, and O is the oxygen anion. Systematic variations of ionic species for A and B, and lengths of the model cube edge were given to the model. Results of charge transfers of the ions show that their magnitudes depend on the edge length; the lager length leads to the higher transfer magnitude. This tendency implies spatial tolerance of the ions to the clusters, and are expected to correlate with electric polarizability and dipole reversibility of this kind of oxides. The density of states and the overlap population indicate that the higher cation valence causes the higher covalency of the anions. Considering all results together provides us an idea to obtain lead-free high-performance ferroelectrics, as high as the lead-based solid solutions.
Highlights
Research and development of lead-free perovskite ferroelectrics have been a subject of the harmless applications, such as actuators mainly and vibration-power generators hopefully, over a decade[1,2,3] since a large number of studies on the lead-based solid solutions were carried out;[4,5,6,7,8] the lead-based studies were those to bring out excellent ferroelectric performances, namely high electric polarization, high piezoelectricity, high electrostriction
We carried out a first-principle cluster calculation in this study and investigated chemical bonds for many ABO3 cases, followed by telling the potentialities of Bi and La from the chemical point of view
A discrete-variational (DV) Xα cluster method and its computer code SCAT19,20 were used for calculating electronic states of ions and their molecular orbitals (MO)
Summary
Research and development of lead-free perovskite ferroelectrics have been a subject of the harmless applications, such as actuators mainly and vibration-power generators hopefully, over a decade[1,2,3] since a large number of studies on the lead-based solid solutions were carried out;[4,5,6,7,8] the lead-based studies were those to bring out excellent ferroelectric performances, namely high electric polarization, high piezoelectricity, high electrostriction. Each transfer value is given by subtracting the effective charge from the formal ionic charge; the values of the cations must be positive and the anions negative, which means transfer of electrons from the anions to the others and formation of covalent bonds among all species.
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