Comparison of oxygen vacancy and interstitial oxygen in KDP and ADP crystals from density functional theory calculations

Point defects may be the main factor to decrease the laser damage threshold of KDP and ADP. By combining the first-principle calculations with the experiments, the oxygen vacancy defect is regarded as one of the dominant source for the initial structural breakdown in KDP which leads to the serious optical damage. The higher laser damage threshold of ADP attributes to a mass of hydrogen bonds that could stabilize the skeleton structure and prevent the electron transitions and optical absorptions. [Display omitted] •Position annihilation technique for KDP and ADP crystals.•The mechanisms induced by oxygen defects based on the first-principle calculations.•The different structural and electrical performance between KDP and ADP crystal. The oxygen vacancy (VO) and interstitial oxygen (Oi) are the easiest formed intrinsic point defects that could decrease the laser damage thresholds of potassium dihydrogen phosphate (KDP) and its analog ammonium dihydrogen phosphate (ADP). In this work, we have grown KDP and ADP crystals by traditional temperature reduction method and “point-seed” rapid growth technique, and proved the existence of the oxygen defects by position annihilation technique. Based on the first-principle calculations, the mechanisms of the structural breakdown and the optical absorption induced by the VO and Oi defects in both crystals have been investigated. It is found that VO2+ and VO0 defects are the dominant point defects that attribute to the collapse of the KDP crystal structure and the weak extra optical absorption at about 155 nm. The higher laser damage threshold of ADP than KDP mainly comes from a mass of hydrogen bonds in ADP crystals. They have found to play an important role in stabilizing the skeleton structure of ADP by forming the strong O-O peroxyl bridge structure and by preventing the electron transitions between and within the NH4 and the PO4 groups. It is therefore suggested to decrease the concentration of VO defects during the growth progress in order to improve the crystal performance under laser irradiation.