Origin of the Abnormal Reduction of the Dielectric Response for ReCOB Crystals and its Mechanism: Theoretical and Experimental Exploration
The dielectric performance of ReCOB (Re: rare earth ion such as Y, Nd, La, etc.) 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 optimize the electro-elastic 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 crystals. The significant decrease in the dielectric permittivity for LaCOB can be attributed to a distinct reduction in the ionic displacement polarization. Charged antisite LaCa+ defects play an important role in improving the dielectric properties of LaCOB by altering the polarization direction. This suggests an effective way to enhance the dielectric performance of LaCOB by increasing the concentration of LaCa antisite defects via partially replacing La3+ with smaller ions such as Y3+, Er3+, and Tm3+, which is beneficial for optimizing the electro-elastic features of ReCOB crystals for piezoelectric sensing application.