Ferroelectric-Paraelectric Transition inBiFeO3: Crystal Structure of the OrthorhombicβPhase

Abstract

A detailed investigation using variable temperature powder neutron diffraction demonstrates that BiFeO 3 undergoes a phase transition from the ferroelectric α phase

Magnetoelectric Ordering of BiFeO3 from the Perspective of Crystal Chemistry

“…The critical distances from the ion centers O, Bi and Fe to the bond line The sign and strength of magnetic couplings in BiFeO 3 was calculated in the temperature range from 25º up to 945º С. We took the crystallographic parameters and atom coordinates in γ-BiFeO 3 [18,32], β-BiFeO 3 [19], α-BiFeO 3 [21] and Bi 0.93 La 0.07 FeO 3 [24], as well as the ionic radii of Fe 3+ , Bi 3+ and O 2-( = 0.645 Ǻ, = 1.17 Ǻ (for γ-and β-BiFeO 3 ), = 1.103 Ǻ (for α-BiFeO 3 ), = 1.40 Ǻ) determined in [59], as initial data for calculations. The method high sensitivity to any slight change of atom coordinates comprises simultaneously its advantage and disadvantage.…”

“…To determine the relation of the above phenomena, we calculated the sign and strength of magnetic couplings in BiFeO 3 on the basis of the structural data [18,19,21,24, 32] at temperatures from 25º up to 945º С (Table 3, Fig. 4).…”

“…First, the process leads to the orthorhombic ß-phase [19] (space group Pbnm with a = 5.613 Å, b = 5.647 Å, and c = 7.971 Å) between 820º C and 830º C and then, in the range 925-933º C, to the cubic -phase [18] (space group m Pm3 with a = 3.992 Å), which decomposes above 960º C. The transition to the cubic phase is accompanied by the insulator-metal transition [18]. Nevertheless, there is still no agreement among the researchers on the transition temperature and symmetry of the paraelectric -phase.…”

“…The experimental studies of BiFeO 3 [18][19][20] established that the temperature increase produced consecutive structural phase transitions from the ferroelectric -phase (rhombohedral space group R3c with a = 5.6 Å, c = 13.9 Å and γ=120) [5,[21][22][23][24][25][26][27]] to two paraelectric phases. First, the process leads to the orthorhombic ß-phase [19] (space group Pbnm with a = 5.613 Å, b = 5.647 Å, and c = 7.971 Å) between 820º C and 830º C and then, in the range 925-933º C, to the cubic -phase [18] (space group m Pm3 with a = 3.992 Å), which decomposes above 960º C. The transition to the cubic phase is accompanied by the insulator-metal transition [18].…”

Phonon spectroscopy near phase transition temperatures in multiferroicBiFeO3epitaxial thin films

“…The first objective is to test the recent space group determination of the γ-phase reported by Arnold et al [1] as being orthorhombic. Their definitive neutron study showed that the γ-phase is indeed stable (which in itself had been controversial), and that it has the same orthorhombic Pbnm orthoferrite symmetry as does the β-phase.…”