ESR Study of 222 K Phase Transition in Hexagonal BaTiO₃

Abstract

Angular dependence of Fe³⁺ ESR spectra in hexagonal BaTiO₃ has been measured around the phase transition temperature of 222 K (T₀). The ESR lines split in three lines respectively in the ab-plane below T₀, and the intensities change with uniaxial stress. These splittings can be explained by the formation of domains. The spin Hamiltonian parameters D and a are −0.059 cm⁻¹ and 0.005 cm⁻¹, respectively, in the both phases. The parameter E is nearly zero above 222 K and increases with decreasing the temperature. The principal axis Z rotates in the bc-plane below T₀. Analysis due to the superposition model indicates that Fe³⁺ substitutes for Ti site in Ti₂O₉ cluster and shifts along the b-axis with decreasing the temperature below T₀.