Crystal Structure Analysis and Phase Transition in Lead Orthovanadate Pb₃(VO₄)₂

Abstract

X-ray scattering experiments of lead orthovanadate, Pb₃(VO₄)₂, were carried out above and below the ferroelectric transition temperature T₂=273 K, using a monodomain crystal. The space groups were confirmed to be C_2h⁵-P2₁⁄c and C₂³-A2 above and below T₂, respectively. The structure analyses were conducted at several temperatures in both phases. The R-factors were less than 0.060 above T₂ and 0.045 below T₂. The spontaneous polarizations were calculated from the atomic positions in the ferroelectric phase and compared with the values observed by the pyroelectric measurement by Midorikawa et al. The mechanism of the ferroelectric phase transition is discussed in terms of the mode of atomic displacements.