High-temperature and high-pressure study on columbite structured ZnNb2O6

TL;DR

This study investigates the structural stability and phase transitions of ZnNb2O6 under high temperature and pressure, revealing a reversible phase change and providing detailed insights into its mechanical properties through experiments and calculations.

Contribution

It provides the first comprehensive high-pressure and high-temperature analysis of columbite ZnNb2O6, including phase transition details and elastic properties.

Findings

Reversible phase transition at 10 GPa from orthorhombic to monoclinic structure.

Bulk modulus increases from 165 GPa to 230 GPa across phases.

Both phases show anisotropic pressure response.

Abstract

High-temperature and high-pressure experiments were conducted on columbite-type ZnNb2O6, reaching temperatures up to 873 K at ambient pressure and pressures up to 30 GPa at ambient temperature, respectively. Through systematic analysis employing synchrotron powder X-ray diffraction and Raman spectroscopy, we examined the crystal structure and phonon behavior. Within the specified temperature range, the orthorhombic phase of ZnNb2O6 (space group: Pbcn) demonstrated notable phase stability, with a thermal expansion coefficient similar to that of isomorphic compounds. Notably, a reversible phase transition was observed under compression at 10 GPa, with diffraction experiments indicating a shift to a monoclinic structure (space group P2/a), which remained stable up to 30 GPa. Changes in Raman modes, lattice parameters, and the unit-cell volume were monitored. A significant 2.5% discontinuity in the unit-cell volume at the phase transition pressure from orthorhombic to monoclinic suggests a first-order phase transition. The bulk moduli of the orthorhombic and monoclinic phases were estimated as 165(7) GPa and 230(9) GPa, respectively- We also found that both phases exhibit an anisotropic response to pressure. Furthermore, first-principles calculations support consistently with experimental observations.