The Dielectric and Piezoelectric Properties of YCa4O(BO3)3 Crystal Annealed in Critical Condition

The YCa
₄
O(BO
₃
)
₃
(YCOB) crystal is an attractive piezoelectric material for sensing at elevated temperatures. In this paper, the dielectric and piezoelectric properties of YCOB crystal annealed at high temperature of 1100°C and low atmosphere pressure of 2 Pa for 24 h were reported. Comparing to the pristine YCOB crystal, the relative dielectric permittivity (ε
₂₂
/ε
₀
) slightly increased after annealing, while the piezoelectric coefficient (d
₂₆
) got decreased, with a variation of <;7%. The chemical bonding for the annealed YCOB was studied using X-ray photoelectron spectroscopy, from which the variations of binding energies of B, Ca, and Y decreased below 0.2 eV, indicating the stable electronic structure of YCOB crystal. The vacancy formation energies for Y, Ca, O, and B atoms in YCOB crystal were also analyzed via first principle calculations. The O atom was found to possess the lowest vacancy formation energy, thus easier to evaporate during critical annealing and easier to compensate than other atoms. The vacancy defects are believed to be the main factor dominant the variations of dielectric and piezoelectric properties.