Synchrotron X-ray analysis of RbTiOAsO4

Area of Science:

• Crystallography
• Materials Science
• Solid-State Chemistry

Background:

• Rubidium oxotitanium arsenate (RbTiOAsO4) is a member of the KTiOPO4 (KTP) family, known for its nonlinear optical properties.
• Understanding cation disorder is crucial for optimizing the performance of KTP-type materials.

Purpose of the Study:

• To accurately determine the crystal structure of RbTiOAsO4 at room temperature using high-resolution synchrotron X-ray diffraction.
• To investigate the charge density distribution and identify the nature of cation disorder in RbTiOAsO4.
• To correlate charge density features with the material's linear and nonlinear optical properties.

Main Methods:

• Single-crystal X-ray diffraction using focused synchrotron radiation (lambda = 0.7500(9) A).
• Data collection at 293 K with a fast avalanche photodiode counter.
• Charge density analysis using difference Fourier transforms (Deltarho) and multipole modeling.

Main Results:

• High-quality synchrotron data revealed splitting of Rb cation positions at room temperature, indicating positional disorder.
• Significant accumulation of difference charge density (Deltarho) near Rb atoms suggests partial occupancy of pseudosymmetric sites.
• Charge density features within Ti-O and As-O bonds correlate with linear and nonlinear optical susceptibility, showing anisotropic behavior.

Conclusions:

• RbTiOAsO4 exhibits temperature-dependent static and/or dynamic disorder of Rb cations, a phenomenon potentially common in the KTP family.
• The observed charge density distribution provides insights into the relationship between crystal structure and nonlinear optical properties.
• Accurate charge density analysis is essential for understanding and predicting the optical behavior of KTP-type materials.