A new β-CdTeO₃ polymorph with a structure related to α-CdTeO₃.

Area of Science:

• Solid State Chemistry
• Materials Science
• Crystallography

Background:

• Polymorphism in metal tellurites is crucial for tuning material properties.
• Understanding the structural and electronic differences between polymorphs is key for materials design.

Purpose of the Study:

• To synthesize and characterize a new polymorph of cadmium tellurite (β-CdTeO₃).
• To elucidate the crystal structure and electronic properties of β-CdTeO₃.
• To compare β-CdTeO₃ with the previously reported α-CdTeO₃ polymorph.

Main Methods:

• Hydrothermal synthesis for β-CdTeO₃ preparation.
• Ab initio structure solution from powder X-ray diffraction data.
• Density Functional Theory (DFT) for electronic structure calculations.
• UV-Vis spectroscopy for optical bandgap determination.

Main Results:

• A new β-CdTeO₃ polymorph with space group Pnma was successfully synthesized.
• The 3D framework of β-CdTeO₃ comprises distorted [CdO₆] octahedra, [CdO₇] prisms, and various tellurium polyhedra ([Te^IVO₃E], [Te^IVO₄E], [Te^IVO₃+₁E]).
• β-CdTeO₃ is a wide bandgap semiconductor (E_g = 3.55 eV), with the presence of [Te^IVO₄E] polyhedra contributing to a lower bandgap compared to α-CdTeO₃ (E_g = 3.91 eV).
• α-CdTeO₃ is slightly more thermodynamically stable than β-CdTeO₃.
• β-CdTeO₃ undergoes a first-order phase transition to α-CdTeO₃ above 540 °C.

Conclusions:

• The study successfully characterized a novel β-CdTeO₃ polymorph, detailing its unique structural features and electronic properties.
• The findings highlight the influence of specific tellurium polyhedra on the semiconductor bandgap of cadmium tellurite.
• The phase transition behavior provides insights into the thermal stability and interconversion of CdTeO₃ polymorphs.