First principles calculation of La₃ Ta_0.5 Ga _5.5 O₁₄ crystal with acceptor-like intrinsic point defects

Langatate (La₃ Ta_0.5 Ga_5.5 O₁₄, LTG) single crystal has been one of the promising candidate piezoelectric materials in high temperature applications because of its structural stability at high temperature. However, it has been reported that compositions of LTG grown by the Czochralski method deviates from the ideal stoichiometry to Ta-poor and Ga-rich material. In this work, to elucidate the energetic stability of defects and their influences on electronic properties, defect formation energies, and electronic properties were calculated for perfect and defective LTG crystals by using first-principles calculations. The results with oxygen-rich assumption showed that Ga substitution on Ta site and Ta vacancy were the most energetically stable defects among various acceptor-like defects under low and high Fermi energy region, respectively. The most stable cation vacancy V Ta ′ ′ ′ ′ ′ could affect the electronic and optical properties of the LTG crystal, as the band gap of a crystal with V Ta ′ ′ ′ ′ ′ has a smaller gap than other defects.