Disorder in the composite crystal structure of the manganese `disilicide' MnSi_1.73 from powder X-ray diffraction data

The crystal structure of the higher manganese silicide MnSi_1.7 (known in the literature as HMS) is investigated in samples with different compositions obtained by different techniques at temperatures not higher than 1273 K. Powder X-ray diffraction was applied. The crystal structure is described as incommensurate composite. In addition to the ordered model already known in the literature, the partial disorder in the silicon substructure was detected and described introducing an additional atomic site with a different modulation function.

Computing details

Cell refinement: WinCSD; data reduction: WinCSD; program(s) used to solve structure: WinCSD; program(s) used to refine structure: WinCSD; software used to prepare material for publication: WinCSD (Akselrud et al., 1993).

(I)

Crystal data

Mn2Si3.5	Z = 2
Tetragonal, I41/amd(00p)00ss†	F(000) = 198.7
q1 = 1.7374c*; q2 = 0.5756c*	Dx = 5.213 Mg m^−3
a = 5.5235 (3) Å	Cu Kα1 radiation, λ = 1.54061 Å
c = 4.3634 (3) Å	T = 295 K
V = 133.13 (2) Å^3	25 × 25 mm

† Symmetry operations: (1) +x₁, +x₂, +x₃, +x₄; (2) −x₁, +x₂, +x₃, 1/2+x₄; (3) 3/4+x₂, 3/4−x₁, 1/4+x₃, +x₄; (4) 1/2+x₁, −x₂, 1/2+x₃, 1/2+x₄; (5) 1/4−x₂, 3/4−x₁, 1/4+x₃, 1/2+x₄; (6) 1/2−x₁, −x₂, 1/2+x₃, +x₄; (7) 1/4+x₂, 1/4+x₁, 3/4+x₃, 1/2+x₄; (8) 3/4−x₂, 1/4+x₁, 3/4+x₃, +x₄; (9) −x₁, −x₂, −x₃, −x₄; (10) +x₁, −x₂, −x₃, −1/2−x₄; (11) −3/4−x₂, −3/4+x₁, −1/4−x₃, −x₄; (12) −1/2−x₁, +x₂, −1/2−x₃, −1/2−x₄; (13) −1/4+x₂, −3/4+x₁, −1/4−x₃, −1/2−x₄; (14) −1/2+x₁, +x₂, −1/2−x₃, −x₄; (15) −1/4−x₂, −1/4−x₁, −3/4−x₃, −1/2−x₄; (16) −3/4+x₂, −1/4−x₁, −3/4−x₃, −x₄; (17) 1/2+x₁, 1/2+x₂, 1/2+x₃, +x₄; (18) 1/2−x₁, 1/2+x₂, 1/2+x₃, 1/2+x₄; (19) 1/4+x₂, 1/4−x₁, 3/4+x₃, +x₄; (20) +x₁, 1/2−x₂, +x₃, 1/2+x₄; (21) 3/4−x₂, 1/4−x₁, 3/4+x₃, 1/2+x₄; (22) −x₁, 1/2−x₂, +x₃, +x₄; (23) 3/4+x₂, 3/4+x₁, 1/4+x₃, 1/2+x₄; (24) 1/4−x₂, 3/4+x₁, 1/4+x₃, +x₄; (25) −1/2−x₁, −1/2−x₂, −1/2−x₃, −x₄; (26) −1/2+x₁, −1/2−x₂, −1/2−x₃, −1/2−x₄; (27) −1/4−x₂, −1/4+x₁, −3/4−x₃, −x₄; (28) −x₁, −1/2+x₂, −x₃, −1/2−x₄; (29) −3/4+x₂, −1/4+x₁, −3/4−x₃, −1/2−x₄; (30) +x₁, −1/2+x₂, −x₃, −x₄; (31) −3/4−x₂, −3/4−x₁, −1/4−x₃, −1/2−x₄; (32) −1/4+x₂, −3/4−x₁, −1/4−x₃, −x₄.

Data collection

Huber Guinier G670 diffractometer	Scan method: step
Radiation source: sealed X-ray tube, GE ID-3003	2θmin = 15.0°, 2θmax = 100.3°, 2θstep = 0.005°
Specimen mounting: packed powder pellet

Refinement

Least-squares matrix: full with fixed elements per cycle	0 parameters
Rp = 0.112	1/sqrt[Yi]
Rwp = 0.087	(Δ/σ)max = 0.032
Profile function: pseudo-Voit

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

	x	y	z	Biso*/Beq	Occ. (<1)
Mn	0	0.25	0.375	0.70 (6)*	0.850 (4)
Si1	0.181 (2)	0.379 (2)	0.825 (3)	0.8 (2)*	0.106 (3)
Mn1	0.181 (2)	0.379 (2)	0.825 (3)	0.8 (2)*	0.019 (3)
Si2	0.25	0	0.75	0.9 (6)*	0.52 (5)