Phase transformation and negative thermal expansion in TaVO5

Area of Science:

• Solid-state chemistry
• Materials science
• Crystallography

Background:

• Understanding phase transformations and thermal expansion is crucial for designing advanced materials.
• Tantalum vanadium oxide (TaVO(5)) is a compound with potential applications requiring knowledge of its structural and thermal properties.

Purpose of the Study:

• To investigate the phase transformations and thermal expansion behavior of TaVO(5).
• To elucidate the structural mechanisms behind the observed phase transitions and negative thermal expansion.

Main Methods:

• Differential scanning calorimetry (DSC) and dilatometry were employed to detect phase transformations.
• X-ray diffraction and neutron powder diffraction were used for structure refinement.
• Calculation of volumetric thermal expansion coefficients (TECs).

Main Results:

• Two phase transformations were identified in TaVO(5).
• A phase transition from monoclinic (P2(1)/c) to orthorhombic (Pnma) symmetry occurs at -14°C.
• TaVO(5) exhibits negative thermal expansion above room temperature, with TECs of -8.92 × 10⁻⁶ °C⁻¹ (20-600°C) and -2.19 × 10⁻⁵ °C⁻¹ (>600°C).

Conclusions:

• The phase transformation at -14°C is driven by the change in regularity of the TaO(6) octahedron.
• Negative thermal expansion is attributed to the tilting of TaO(6) and VO(4) polyhedra, leading to increased Ta-O-V angles and shrinkage of VO(4) tetrahedra upon heating.