Structure of Ti₂P solved by three-dimensional electron diffraction data collected with the precession technique and high-resolution electron microscopy

The crystal structure of Ti₂P has been analysed using electron diffraction and high-resolution electron-microscopy techniques. A new unit cell was found, the compound is hexagonal with a = 19.969 (1) and c = 3.4589 (1) Å. The structure was first solved in space group in projection using direct methods on electron diffraction data from the [001] zone axis. A three-dimensional solution was obtained using again direct methods but on a three-dimensional set of electron diffraction data recorded with the precession technique. Ti₂P is a distorted Fe₂P structure and, based on high-resolution images, it is possible to explain that the tripling of the unit cell is due to the ordering of P vacancies that reduces the symmetry to .

Computing details

Data collection: QED (Belletti, Calestani, Gemmi, Migliori, Ultramicroscopy, 2000, 81, 57-65) CRISP (Hovmöller, Ultramicroscopy, 1992, 41, 121-125); cell refinement: GSAS (Larson and Von Dreele 1994); program(s) used to solve structure: SIR97(Cascarano al.,Acta Cryst.,1996,A52,C-79).

(I)

Crystal data

Ti2P	c = 3.4589 (1) Å
Mr = 3421.81	V = 1194.5 (1) Å^3
Hexagonal, P62m	Z = 27
a = 19.969 (1) Å	T = 295 K

Data collection

Philips CM30T diffractometer	Rint = 0.22
Radiation source: thermoionic electron gun	h = 0→15
precessed electron diffraction scans	k = −7→0
98 measured reflections	l = 0→2

Special details

Experimental. Structure solved by electron diffraction data collected with precession tecnique·Microscope used: Philps CM30T Accelerating voltage 300 kV

Refinement. The structure was solved using direct methods on precessed electron diffraction data. Because of the dynamical effects the quality of the data did not allowed the structure refinement. The errors reported in the atomic positions are just an estimate calculated on the basis of one cycle of refinement.

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

	x	y	z	Biso*/Beq
TI1	0.427 (6)	0.093 (6)	0.5000
TI2	0.239 (8)	0.0000	0.5000
TI3	0.330 (6)	0.133 (6)	0.0000
TI4	0.472 (8)	0.0000	0.0000
TI5	0.098 (8)	0.098 (8)	0.5000
TI6	0.755 (5)	0.424 (7)	0.5000
TI7	0.136 (8)	0.0000	0.0000
TI8	0.878 (6)	0.545 (6)	0.0000
TI9	0.800 (7)	0.330 (8)	0.0000
TI10	0.206 (6)	0.206 (6)	0.0000
TI11	1.0000	0.590 (7)	0.5000
TI12	0.335 (6)	0.245 (6)	0.5000
P1	0.6667	0.3333	0.0000
P2	0.0000	0.0000	0.0000
P3	0.33 (1)	0.0000	0.0000
P4	0.444 (7)	0.23 (1)	0.5000
P5	0.225 (7)	0.117 (9)	0.5000
P6	0.55 (1)	0.108 (7)	0.5000
P7	0.328 (10)	0.328 (10)	0.0000

Bond lengths (Å)

TI1—TI1^i	3.21 (15)	P3—TI1	2.57 (10)
TI1—TI2	3.3 (2)	P3—TI3	2.66 (16)
TI1—TI3	2.99 (17)	P3—TI4	2.8 (3)
TI1—TI4	2.99 (15)	P4—TI6^v	2.4 (3)
TI1—TI9^ii	2.72 (10)	P4—TI12	2.3 (2)
TI2—TI3	2.92 (8)	P4—TI1	2.6 (2)
TI2—TI7	2.69 (17)	P4—TI8^vii	2.61 (17)
TI3—TI12	2.79 (14)	P4—TI9^ii	2.70 (19)
TI4—TI11^iii	2.92 (14)	P4—TI3	2.74 (11)
TI5—TI5^iv	3.4 (2)	P5—TI2	2.5 (2)
TI5—TI7	2.98 (18)	P5—TI3	2.61 (15)
TI5—TI10	2.76 (11)	P5—TI5	2.4 (2)
TI6—TI6^ii	3.10 (17)	P5—TI7	2.73 (10)
TI6—TI8	2.99 (9)	P5—TI10	2.64 (19)
TI6—TI9	3.00 (19)	P5—TI12	2.40 (14)
TI6—TI9^v	2.87 (18)	P6—TI1	2.3 (2)
TI8—TI11	2.75 (8)	P6—TI4	2.59 (8)
TI8—TI12^iii	2.76 (13)	P6—TI6^ii	2.57 (14)
TI10—TI12	2.87 (14)	P6—TI8^ii	2.81 (19)
TI11—TI12^ii	2.86 (19)	P6—TI9^ii	2.69 (19)
TI12—TI12^vi	3.1 (2)	P6—TI11^ii	2.7 (2)
P1—TI6	2.49 (6)	P7—TI8^v	2.5 (3)
P1—TI9	2.71 (16)	P7—TI10	2.47 (17)
P2—TI5	2.61 (8)	P7—TI11^v	2.35 (10)
P2—TI7	2.72 (16)	P7—TI12	2.46 (19)
P3—TI2	2.51 (18)

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