ACaBO₃ (A = Cs, Rb): two new cubic borates with isolated BO₃ groups.

Area of Science:

• Solid-state chemistry
• Materials science
• Crystallography

Background:

• Alkali and alkaline-earth metal borates are of interest for their optical properties.
• Cubic borate structures are challenging to achieve due to anisotropic BO₃ triangles.
• Understanding structure-property relationships is key for designing new materials.

Purpose of the Study:

• Synthesize and characterize novel cubic alkali and alkaline-earth metal borates.
• Investigate the second-harmonic generation (SHG) properties and band gap of CsCaBO₃.
• Elucidate the structural factors governing the formation of cubic borate frameworks.

Main Methods:

• High-temperature solution method for synthesis.
• Powder SHG response measurement.
• Experimental band gap determination.
• Crystallographic analysis of cubic space group P2₁3.
• Computational SHG density calculations.

Main Results:

• Successfully synthesized CsCaBO₃ and RbCaBO₃.
• CsCaBO₃ shows a powder SHG response comparable to potassium dihydrogen phosphate (KDP) with a band gap of 4.20 eV.
• SHG effect in CsCaBO₃ arises from the synergistic interaction of B-O and Ca-O groups.
• The crystal structure features a 3D framework of CaO₆ octahedra, CsO₉ polyhedra, and BO₃ triangles.
• MO₆ octahedra are identified as crucial for forming ordered cubic structures with BO₃ or B₂O₅ groups.

Conclusions:

• CsCaBO₃ is a promising material for nonlinear optical applications.
• The role of MO₆ octahedra in stabilizing cubic borate structures is significant.
• This study provides essential insights for designing new cubic borates containing BO₃ triangles.