Antisite defect “conductivity barrier” and 5d orbital hybridization for enhanced resistivity in piezoelectric crystals

Abstract

Piezoelectric crystals are extensively employed in sensing technologies, yet their intrinsic low resistivity at elevated temperatures poses a critical challenge, significantly hindering their application in high-temperature environments. It is found that Ta-containing piezoelectric crystals possess higher resistivity than their Nb-containing counterparts, but the underlying mechanisms remain unclear. Herein, we propose a novel electron relaxation mechanism that highlights the 5d orbital hybridization induced efficient electron trapping in antisite defects through a comparative analysis of La₃Ga_5.5Ta_0.5O₁₄ (LGT) and La₃Ga_5.5Nb_0.5O₁₄ (LGN) crystals. Our study reveals that the spatial extension of Ta-5d orbitals strengthens hybridization with O-2p orbitals, significantly increasing the crystal field splitting energy and deepening the Ta_Ga polaron potential well, which collectively elevate the excitation energy for electron release, accelerate the carrier recombination, and ultimately suppress electrical conductivity while boosting resistivity. Leveraging this mechanism, LGT crystal features a remarkable three-orders-of-magnitude enhancement in resistivity by co-regulation of electron concentration, antisite defect density and occupation sites via combining oxygen atmospheric control and Al doping. This study provides a new insight into the conduction mechanism and a general Ta-based design strategy for resistivity modulation beyond the piezoelectric crystals.