Symmetry-mode analysis of the ferroelectric transition in YMnO_3

摘要

Group theoretical methods were applied to elucidate the structural transition path and the polarization process in YMnO_3. The atomic displacements derived from in situ high-temperature synchrotron x-ray powder diffraction data were decomposed into three symmetry-adapted modes (Γ_2~-, K_1, and K_3). The temperature dependence of the mode amplitudes confirmed the existence of two step-transitions. First, a coupled K_3 and Γ_2~- mode lowered the symmetry from P6_3/mmc to P6_3cm at the phase-transition temperature of ~ 1270 K, and held down to the T_c. A single K_3 mode, stabilized by hybridization between the Y and in-plane O ions, operated below T_c with no additional symmetry breakage.