Abstract
The effective ionic charges of lead-free perovskite dielectric complex compounds were investigated with molecular orbital calculation. The base model was a double perovskite cluster that consisted of octahedral oxygen cages with a transition metal ion of titanium, niobium, or zirconium located at each of their centers, and alkali and/or alkaline earth metal ions located at the body center, corners, edge centers, or face centers of the cluster. The results showed significant covalent bonds between the transition metals and the oxygens, and the alkali metals, especially sodium and oxygen. On the other hand, the alkaline earth metals have weak covalency. Calculation was also performed with the replacement of some of the oxygens with chlorine or fluorine; such replacement enhances the covalency of the transition metals. These trends provide good guidelines for the design properties of lead-free perovskite piezoelectrics based on ubiquitous sodium use.
Highlights
Lead (Pb)-based piezoelectrics have exclusively high electric polarization and piezoelectricity [1,2,3,4,5].The typical substance is lead titanate, designated as PbTiO3 (PT) [6,7]
The effective ionic charges of perovskite dielectric complex compounds were investigated with molecular orbital calculation
The charge of Pb for PT, which is an important component of good piezoelectrics, was a stand-alone value
Summary
Lead (Pb)-based piezoelectrics have exclusively high electric polarization and piezoelectricity [1,2,3,4,5].The typical substance is lead titanate, designated as PbTiO3 (PT) [6,7]. The results indicated that the lead (Pb) ion is significantly covalent with the oxygen (O) and titanium (Ti) ions This feature suggests that the covalency forms a molecular orbital (i.e., electronic channels) through which valence electrons are transferred back and forth between the cations and anions in response to external fields. Takesue [9], confirmed with molecular orbital calculation that (Bi1/2 Na1/2 )TiO3 (BNT) [10,11] could be such a substitute. This substance is widely recognized as a potential substitute and has been studied through many types of fabrication [11,12,13], long before N. In addition to BNT, many excellent Pb-free piezoelectrics have been discovered [14,15,16]
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