Oxygen and potassium vacancies in KTP calculated from first principles

Area of Science:

• Materials Science
• Solid State Physics
• Computational Chemistry

Background:

• Potassium titanyl phosphate (KTP) is a widely used nonlinear optical material.
• Understanding point defects, such as vacancies, is crucial for optimizing KTP's properties.
• Previous studies have explored KTP's defect behavior, but a comprehensive analysis of charge-state-dependent properties is needed.

Purpose of the Study:

• To investigate the atomic geometry, energetics, electronic, and optical properties of oxygen and potassium vacancies in KTP.
• To determine the influence of different charge states on these vacancy properties.
• To elucidate the impact of vacancies on KTP's optical response.

Main Methods:

• Density-functional theory (DFT) calculations were employed.
• The study systematically analyzed oxygen vacancies (between Ti-P and Ti-Ti) and potassium vacancies.
• Calculations considered various charge states and their dependence on the Fermi level.

Main Results:

• Oxygen vacancies between Ti and P exhibit negative-U behavior, with the neutral charge state (favored near the conduction band) introducing a defect level and an optical absorption peak.
• The doubly positive charge state of these Ti-P oxygen vacancies slightly alters the optical response.
• Oxygen vacancies between Ti atoms are doubly positive, and potassium vacancies are negative, neither significantly affecting KTP's optical properties.

Conclusions:

• The charge state of oxygen vacancies significantly influences their electronic and optical properties in KTP.
• Neutral oxygen vacancies near the conduction band are key to understanding optical absorption changes.
• Potassium vacancies and certain oxygen vacancies have minimal impact on KTP's optical characteristics.