Pressure-Induced Structural Transition to the Polar Phase in GdFe3(BO3)4

The GdFe3(BO3)4 crystal has attracted great interest as a magnetic-field-induced multiferroic. In this paper, we show that multiferroic properties in this crystal can be induced by high pressure. At high pressures up to 50 GPa, created in diamond anvil cells, the structural and vibrational (phonon) properties of the GdFe3(BO3)4 crystal were studied. The structural phase transition was detected at about 23–25 GPa by Raman and synchrotron Mossbauer (NFS) spectroscopy. First-principle calculations of the crystal lattice dynamics at pressures below and above the structural transition were carried out. It was established that at pressures above the structural transition, the space group R32 of GdFe3(BO3)4 is changed to the polar space group R3 and the crystal becomes a ferroelectric. At the R32 → R3 transition, the displacement of the boron ion B(2) and oxygen O results in the formation of boron-oxygen tetrahedrons B(2)O4 instead of the plane BO3 triangles. Meanwhile, the triangle oxygen environment of boron i...