A new polar alkaline earth-rare earth iodate: Ba₂Ce(IO₃)₈(H₂O)

Area of Science:

• Inorganic Chemistry
• Materials Science
• Crystallography

Background:

• Alkaline earth-rare earth iodates are of interest due to their unique structural and optical properties.
• Hydrothermal synthesis offers a versatile route for creating novel crystalline materials.
• Understanding structure-property relationships is crucial for designing advanced functional materials.

Purpose of the Study:

• To synthesize and characterize a new alkaline earth-rare earth iodate, Ba2Ce(IO3)8(H2O).
• To determine the crystal structure of Ba2Ce(IO3)8(H2O) using single-crystal X-ray diffraction.
• To investigate the optical properties, specifically UV-vis-NIR transmission and second-harmonic-generation (SHG) response, and their correlation with the crystal structure.

Main Methods:

• Hydrothermal synthesis for crystal growth.
• Single-crystal X-ray diffraction for structural determination.
• UV-vis-NIR transmission spectroscopy for optical absorption analysis.
• Theoretical calculations for band gap and property analysis.

Main Results:

• Ba2Ce(IO3)8(H2O) was successfully synthesized as large crystals.
• The crystal structure was determined, revealing zero-dimensional [Ce(IO3)8(H2O)]4- units and polar space group Pna21.
• The compound exhibits a short wavelength absorption edge at 381 nm and a weak SHG response (0.2 times that of KDP).
• A theoretical band gap of 2.44 eV was calculated, influenced by Ce-O and I-O interactions.

Conclusions:

• The synthesis of Ba2Ce(IO3)8(H2O) expands the family of alkaline earth-rare earth iodates.
• The weak SHG response is attributed to the cancellation of polarization effects from iodate groups.
• The study highlights the strong correlation between crystal structure, functional group arrangement, and optical properties like SHG and birefringence.
• The presence of alkaline earth metals appears to increase the band gap in these compounds.