Magnetic and nuclear structure of goethite (α-FeOOH): a neutron diffraction study

The magnetic structure of two natural samples of goethite (α-FeOOH) with varying crystallinity was analyzed at 15 and 300 K by neutron diffraction. The well crystallized sample has the Pb′nm color space group and remained antiferromagnetic up to 300 K, with spins aligned parallel to the c axis. The purely magnetic 100 peak, identifying this color space group, was clearly resolved. The nanocrystalline sample shows a phase transition to the paramagnetic state at a temperature below 300 K. This lowering of the Néel temperature may be explained by the interaction of magnetic clusters within particles. The nuclear structure, refined with the Rietveld and pair distribution function methods, is consistent with reports in the literature.

Computing details

(NPDF_07102_phase_1)

Crystal data

FeHO2	c = 3.01333 (3) Å
Mr = 88.85	V = 137.72 (1) Å^3
Orthorhombic, Pbnm	Z = 4
Hall symbol: Pbnm	? radiation, λ = ? Å
a = 4.59748 (4) Å	T = 15 K
b = 9.94115 (9) Å	?, ? × ? × ? mm

Data collection

Refinement

Least-squares matrix: full	? data points
Rp = ?	81 parameters
Rwp = ?	0 restraints
Rexp = ?	(Δ/σ)max = 0.28
χ^2 = 3.497

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

	x	y	z	Uiso*/Ueq
Fe1	0.04833 (14)	0.85378 (9)	0.25	0.0060 (4)*
O1	0.7057 (3)	0.20032 (13)	0.25	0.0011 (5)*
O2	0.2013 (3)	0.05335 (12)	0.25	0.0051 (5)*
H1	0.4024 (6)	0.0823 (2)	0.25	0.0189 (6)*

Geometric parameters (Å, º)

Fe1—O1^i	1.9211 (19)	O1—Fe1^iii	1.9592 (9)
Fe1—O1^ii	1.9592 (9)	O1—H1	1.822 (2)
Fe1—O1^iii	1.9592 (9)	O2—Fe1^viii	2.1049 (13)
Fe1—O2^iv	2.1049 (13)	O2—Fe1^v	2.1070 (9)
Fe1—O2^v	2.1070 (9)	O2—Fe1^vi	2.1070 (9)
Fe1—O2^vi	2.1070 (9)	O2—H1	0.969 (3)
O1—Fe1^vii	1.9211 (19)	H1—O1	1.822 (2)
O1—Fe1^ii	1.9592 (9)	H1—O2	0.969 (3)
O1^i—Fe1—O1^ii	97.64 (3)	O2^iv—Fe1—O2^v	76.64 (6)
O1^i—Fe1—O1^iii	97.64 (3)	O2^iv—Fe1—O2^vi	76.64 (6)
O1^i—Fe1—O2^iv	162.08 (7)	O2^v—Fe1—O2^vi	91.30 (5)
O1^i—Fe1—O2^v	90.97 (5)	Fe1^vii—O1—Fe1^ii	124.67 (4)
O1^i—Fe1—O2^vi	90.97 (5)	Fe1^vii—O1—Fe1^iii	124.67 (4)
O1^ii—Fe1—O1^iii	100.53 (6)	Fe1^ii—O1—Fe1^iii	100.53 (6)
O1^ii—Fe1—O2^iv	93.78 (5)	Fe1^viii—O2—Fe1^v	103.36 (6)
O1^ii—Fe1—O2^v	83.38 (4)	Fe1^viii—O2—Fe1^vi	103.36 (6)
O1^ii—Fe1—O2^vi	169.94 (6)	Fe1^viii—O2—H1	126.79 (15)
O1^iii—Fe1—O2^iv	93.78 (5)	Fe1^v—O2—Fe1^vi	91.30 (5)
O1^iii—Fe1—O2^v	169.94 (6)	Fe1^v—O2—H1	112.95 (11)
O1^iii—Fe1—O2^vi	83.38 (4)	Fe1^vi—O2—H1	112.95 (11)

Symmetry codes: (i) −x+1/2, y+1/2, z; (ii) −x+1, −y+1, z−1/2; (iii) −x+1, −y+1, z+1/2; (iv) x, y+1, z; (v) −x, −y+1, z−1/2; (vi) −x, −y+1, z+1/2; (vii) −x+1/2, y−1/2, z; (viii) x, y−1, z.

(NPDF_07102_phase_2)

Crystal data

Fe	c = 3.01333 (3) Å
Mr = 55.85	V = 137.72 (1) Å^3
Orthorhombic, Pbnm	Z = 4
Hall symbol: Pbnm	? radiation, λ = ? Å
a = 4.59748 (4) Å	T = 15 K
b = 9.94115 (9) Å	?, ? × ? × ? mm

Data collection

Refinement

Least-squares matrix: full	? data points
Rp = ?	81 parameters
Rwp = ?	0 restraints
Rexp = ?	(Δ/σ)max = 0.28
χ^2 = 3.497

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

	x	y	z	Uiso*/Ueq
Fe1	0.04833 (14)	0.85378 (9)	0.25	0.0060 (4)*