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.
@article{arxiv.2508.03658,
title = {High-temperature and high-pressure study on columbite structured ZnNb2O6},
author = {A. Tyagi and P. Botella and A. B. Garg and J. Sanchez-Martin and D. Diaz-Anichtchenko and R. Turnbull and S. Anzellini and C. Popescu and D. Errandonea},
journal= {arXiv preprint arXiv:2508.03658},
year = {2025}
}