Anisotropic microstrain broadening in cementite, Fe₃C, caused by thermal microstress: comparison between prediction and results from diffraction-line profile analysis

X-ray powder diffraction data of an Fe₃C powder consisting of polycrystalline particles shows pronouncedly anisotropic microstrain broadening of the Bragg reflections. The extent and anisotropy of the broadening can quantitatively be attributed to thermal microstresses induced by anisotropic thermal shrinkage from the preparation temperature of 873 K to the ambient analysis temperature, in conjunction with the elastic anisotropy of Fe₃C.

Computing details

(Structure1)

Crystal data

Fe3C	β = 90°
Mr = ?	γ = 90°
?, ?	V = 155.50 (1) Å^3
a = 5.09100 (1) Å	Z = 4
b = 6.74692 (2) Å	X-ray radiation, λ = 1.78897 Å
c = 4.52711 (1) Å	T = 300 K
α = 90°	?, 15 × 15 mm

Data collection

Radiation source: sealed X-ray tube	Scan method: continuous
Graphite 002 monochromator	2θmin = 19.984°, 2θmax = 139.992°, 2θstep = 0.009°
Data collection mode: reflection

Refinement

Rp = 0.018	Profile function: FPA analysed on the basis of LaB6 pattern, anisotropic microstrain broadening
Rwp = 0.024	Weighting scheme based on measured s.u.'s
Rexp = ?
R(F) = 0.008	Background function: Chebychev Polynoms 10th order
χ^2 = NOT FOUND	Preferred orientation correction: none
15002 data points

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

	x	y	z	Biso*/Beq
Fe	0.17883 (5)	0.06704 (4)	0.33533 (7)	0.500 (6)
Fe	0.03744 (6)	0.25	0.83921 (11)	0.500 (6)
C	0.8791 (3)	0.25	0.4403 (4)	0.500 (6)