Ultrastiff cubic TiO2 identified via first-principles calculations

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Titanium dioxide (TiO2) exists in various crystal structures, each with unique physical properties.
• Understanding the compressibility and mechanical behavior of TiO2 polymorphs under pressure is crucial for materials science applications.

Purpose of the Study:

• To calculate and compare the crystal structures and compressibilities of fluorite- and pyrite-structured TiO2 under hydrostatic pressure.
• To evaluate the potential of these TiO2 polymorphs as ultrahard materials.

Main Methods:

• Utilized gradient-corrected density functional theory (DFT) and hybrid density functional-Hartree-Fock (HF) formulations.
• Performed calculations on fluorite- and pyrite-structured TiO2 under varying hydrostatic pressures.

Main Results:

• Fluorite TiO2 demonstrated high incompressibility with a bulk modulus (K(0)) of approximately 395 GPa, nearing ultrahard cotunnite TiO2.
• Pyrite TiO2 showed a smaller bulk modulus (K(0) of approximately 220-260 GPa), yet exceeding experimental values for cubic TiO2.
• Calculated shear modulus values suggest fluorite TiO2 could be an ultrahard material if stabilized.

Conclusions:

• Fluorite TiO2 is a highly incompressible material with potential for ultrahard applications.
• The mechanical properties of different TiO2 polymorphs vary significantly with crystal structure.
• Further research is needed to stabilize fluorite TiO2 under ambient conditions for practical use.