Structure modulations in nonlinear optical (NLO) materials Cs(2)TB4O9 (T = Ge, Si)

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Inorganic borates are crucial for nonlinear optical (NLO) applications.
• Understanding complex crystal structures is key to designing new NLO materials.
• Previous studies on Cs(2)TB4O9 lacked detailed structural insights.

Purpose of the Study:

• To elucidate the incommensurately modulated structures of Cs(2)TB4O9 (T = Ge, Si).
• To explain the origin of unusual bond distances observed in average structures.
• To provide a foundation for the design of novel NLO borate materials.

Main Methods:

• Single-crystal X-ray diffraction was employed for detailed structural analysis.
• The charge-flipping algorithm was used to solve the complex modulated structures.
• Superspace group symmetry I2(αβ0)0 was determined for the crystal structures.

Main Results:

• New types of incommensurately modulated borate structures were identified in Cs(2)TB4O9.
• The primary modulation feature was determined to be the ordering of oxygen atoms.
• The modulated structure models successfully explained the previously observed unreasonable B-O distances, attributing them to the ordering of BO4 and BO3 units.

Conclusions:

• The detailed structural analysis reveals a new type of modulated borate structure.
• Oxygen ordering is the key factor driving the structural complexity in Cs(2)TB4O9.
• This work provides a deeper understanding of structure-property relationships in NLO borates.