Deformations of the α-Fe₂O₃ rhombohedral lattice across the Néel temperature

High-resolution synchrotron radiation powder diffraction patterns of α-Fe₂O₃ measured between room temperature and 1100 K, i.e. above the Néel temperature T_N = 950 K, have been analyzed. The integral breadths of the Bragg peaks show a hkl-dependent anisotropy, both below and above T_N. This anisotropy can be quantitatively described by using a statistical peak-broadening model [Stephens (1999). J. Appl. Cryst. 32, 281]. Model calculations show that the rhombohedral α-Fe₂O₃ lattice is deformed and the deformation leads to a monoclinic lattice with the unique monoclinic axis along the hexagonal [110] direction both below and above T_N. The monoclinic symmetry of bulk α-Fe₂O₃ is compatible with α-Fe₂O₃ nanowire growth along the [110] direction reported in Fu et al. [Chem. Phys. Lett. (2001), 350, 491].

Computing details

(I)

Crystal data

Fe2O3	β = 162.4043 (3)°
Mr = 159.7	V = 201.35 (1) Å^3
Monoclinic, C2/c	Z = 4
Hall symbol: -C 2yc	F(000) = 304
a = 9.61865 (9) Å	Dx = 5.268 Mg m^−3
b = 5.03554 (3) Å	Synchrotron radiation
c = 13.75158 (13) Å	T = 293 K

Data collection

2θmin = 5°, 2θmax = 29.999°, 2θstep = 0.001°

Refinement

Rp = 0.097	21 parameters
Rwp = 0.129	0 restraints
Rexp = 0.094	0 constraints
R(F) = 0.032	Weighting scheme based on measured s.u.'s
43005 data points	(Δ/σ)max = 0.025
Excluded region(s): from 30 to 100.000	Background function: 5 Legendre polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Fe1	0	0	0.14473 (3)	0.0033*
O1	0	0.309 (3)	0.25	0.0005*
O2	−0.449 (2)	−0.156 (2)	−0.050 (2)	0.0005*

(II)

Crystal data

Fe2O3	β = 162.3508 (2)°
Mr = 159.7	V = 206.97 (1) Å^3
Monoclinic, C2/c	Z = 4
Hall symbol: -C 2yc	F(000) = 304
a = 9.68920 (8) Å	Dx = 5.125 Mg m^−3
b = 5.08737 (2) Å	Synchrotron radiation
c = 13.84868 (11) Å	T = 1053 K

Data collection

2θmin = 5°, 2θmax = 29.999°, 2θstep = 0.001°

Refinement

Rp = 0.099	21 parameters
Rwp = 0.128	0 restraints
Rexp = 0.086	0 constraints
R(F) = 0.044	Weighting scheme based on measured s.u.'s
43003 data points	(Δ/σ)max = 0.036
Excluded region(s): from 30 to 100.000	Background function: 5 Legendre polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Fe1	0	0	0.14425 (3)	0.0131*
O1	0	0.313 (3)	0.25	0.0102*
O2	−0.449 (3)	−0.155 (3)	−0.049 (2)	0.0102*