Prediction of ultraviolet optical materials in the K₂O-B₂O₃ system

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Ultraviolet (UV) birefringent crystals are essential for advanced technologies like lasers and optical communications.
• Alkali metal borates are a promising class of materials due to their diverse structures and UV optical properties.

Purpose of the Study:

• To systematically explore the K2O-B2O3 system for novel UV birefringent crystals.
• To identify stable and metastable crystal structures and analyze their properties.

Main Methods:

• Utilized the evolutionary crystal structure prediction algorithm USPEX.
• Performed ionic substitutions and first-principles calculations.
• Analyzed structural, electronic, and optical properties of predicted structures.

Main Results:

• Predicted two new stable structures (oP56-K3BO3 and mC44-K4B2O5) and twelve metastable structures in the K2O-B2O3 system.
• Identified six candidate structures with wide band gaps and high birefringence for UV optical applications.
• Discovered hR21-K3BO3, a non-centrosymmetric structure with a significant frequency doubling coefficient (4.6 KDP) and birefringence (0.056@1064 nm).

Conclusions:

• The coplanar arrangement of BO3 and B3O6 groups enhances optical anisotropy and birefringence.
• hR21-K3BO3 is a highly promising UV nonlinear optical material.
• The K2O-B2O3 system offers a rich source of novel UV optical materials.