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High-pressure monoclinic-monoclinic transition in fergusonite-type HoNbO4
A B Garg1,2, D Errandonea3, P Rodríguez-Hernández4
1High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Summary
High-pressure studies reveal fergusonite-type HoNbO₄ undergoes a reversible phase transition at 18.9 GPa. This transition, driven by mechanical instabilities, changes niobium coordination and differs from related niobates.
Area of Science:
- Materials Science
- Solid State Physics
- Crystallography
Background:
- Fergusonite-type HoNbO₄ is a material with potential applications.
- Understanding its structural behavior under high pressure is crucial for its technological use.
Purpose of the Study:
- To investigate the high-pressure structural behavior of fergusonite-type HoNbO₄.
- To characterize the phase transition and its driving mechanisms.
- To determine the material's equation of state and compressibility.
Main Methods:
- High-pressure powder x-ray diffraction experiments.
- Ab initio density-functional theory (DFT) simulations.
- Ambient-pressure Raman and infrared spectroscopy.
Main Results:
- A reversible phase transition from monoclinic I2/a to monoclinic P2₁/c structure at 18.9(1.1) GPa.
- The high-pressure phase is stable up to 29 GPa, involving a change in Nb coordination from 4 to 6.
- Determination of pressure-dependent unit-cell parameters, equation of state, and isothermal compressibility.
- Identification of all active Raman and IR modes, supported by DFT calculations.
Conclusions:
- The phase transition in HoNbO₄ is driven by mechanical instabilities and phonon softening.
- The observed high-pressure behavior is distinct from that of related niobates.
- DFT calculations accurately predict structural, elastic, and spectroscopic properties.
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