Origin of the abnormal reduction of the dielectric response for ReCOB crystals and its mechanism: theoretical and experimental exploration

Abstract

The dielectric performance of ReCOB-type (Re: rare earth ions) crystals is vital for modulating their electro-elastic properties and improving the sensing capabilities of such high temperature piezoelectric sensors. It has been reported that the dielectric permittivity of ReCOB increases with increasing Re³⁺ ion radius, whereas LaCOB exhibits an abnormal drop in the dielectric permittivity, which presents an obstacle to the optimization of the properties of ReCOB crystals. By using first-principle calculations and combining these with experiments, we found that both electronic hybridization and bond vibrations contribute to the dielectric permittivity of ReCOB. A significant decrease in dielectric permittivity for LaCOB can be attributed to the distinct reduction in the ionic displacement polarization. Charged antisite La_Ca⁺ defects play an important role in improving the dielectric properties of LaCOB by changing the polarization direction. This suggests that it would be useful to increase the concentration of La_Ca antisite defects by partially replacing La³⁺ with smaller ions, such as Y³⁺, Er³⁺, and Tm³⁺.