Redetermination of Nd2Ti2O7: a non-centrosymmetric structure with perovskite-type slabs.

Single crystals of dineodymium(III) dititanium(IV) hepta-oxide, Nd2Ti2O7, were synthesized by the flux method and found to belong to the family of compounds with perovskite-type structural motifs. The asymmetric unit contains four Nd, four Ti and 14 O-atom sites. The perovskite-type slabs are stacked parallel to (010) with a thickness corresponding to four corner-sharing TiO6 octa-hedra. The Nd and Ti ions are displaced from the geometrical centres of respective coordin-ation polyhedra so that the net polarization occurs along the c axis. The investigated crystals were all twinned and have a halved monoclinic unit cell in comparison with the first structure determination of this compound [Scheunemann & Müller-Buschbaum (1975 ▶). J. Inorg. Nucl. Chem. 37, 2261-2263].

Related literature

For previous determinations of Nd2Ti2O7, see: Scheunemann & Müller-Buschbaum (1975 ▶); Harvey et al. (2005 ▶). For related compounds, see: Gasperin (1975 ▶); Ishizawa et al. (1980 ▶); Schmalle et al. (1993 ▶). For the extinction method, see: Becker & Coppens (1974 ▶).

Experimental

Crystal data

Nd2Ti2O7

M = 496.2

Monoclinic,

a = 7.6747 (1) Å

b = 13.0025 (2) Å

c = 5.4640 (1) Å

γ = 98.5165 (5)°

V = 539.24 (2) Å3

Z = 4

Mo Kα radiation

μ = 21.77 mm−1

T = 293 K

0.11 × 0.08 × 0.07 mm

Data collection

Bruker APEXII CCD diffractometer

Absorption correction: multi-scan (TWINABS; Bruker, 2008 ▶) T min = 0.134, T max = 0.206

25187 measured reflections

6608 independent reflections

6200 reflections with I > 3σ(I)

R int = 0.049

Refinement

R[F 2 > 2σ(F 2)] = 0.024

wR(F 2) = 0.027

S = 1.37

6608 reflections

133 parameters

Δρmax = 2.44 e Å−3

Δρmin = −1.57 e Å−3

Absolute structure: Flack (1983 ▶), 3019 Friedel pairs

Flack parameter: 0.220 (12)

Data collection: APEX2 (Bruker, 2008 ▶); cell refinement: SAINT (Bruker, 2008 ▶); data reduction: SAINT; program(s) used to solve structure: SUPERFLIP (Palatinus & Chapuis, 2007 ▶); program(s) used to refine structure: JANA2006 (Petříček et al., 2006 ▶); molecular graphics: ATOMS (Dowty, 2006 ▶) and DIAMOND (Brandenburg & Putz, 2005 ▶); software used to prepare material for publication: PLATON (Spek, 2009 ▶) and publCIF (Westrip, 2010 ▶).

Click here for additional data file.

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536813005497/wm2720sup1.cif

Click here for additional data file.

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536813005497/wm2720Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Nd2Ti2O7	F(000) = 880
Mr = 496.2	Dx = 6.110 Mg m−3
Monoclinic, P1121	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: P 2zc	Cell parameters from 12720 reflections
a = 7.6747 (1) Å	θ = 3.2–40.2°
b = 13.0025 (2) Å	µ = 21.77 mm−1
c = 5.4640 (1) Å	T = 293 K
β = 90°	Block, purple
V = 539.24 (2) Å3	0.11 × 0.08 × 0.07 mm
Z = 4

Bruker APEXII CCD diffractometer	6200 reflections with I > 3σ(I)
Radiation source: X-ray tube	Rint = 0.049
φ and ω scans	θmax = 40.3°, θmin = 1.6°
Absorption correction: multi-scan (TWINABS; Bruker, 2008)	h = −13→13
Tmin = 0.134, Tmax = 0.206	k = −23→23
25187 measured reflections	l = −9→9
6608 independent reflections

Refinement on F	Weighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0001F2)
R[F2 > 2σ(F2)] = 0.024	(Δ/σ)max = 0.016
wR(F2) = 0.027	Δρmax = 2.44 e Å−3
S = 1.37	Δρmin = −1.57 e Å−3
6608 reflections	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
133 parameters	Extinction coefficient: 349 (12)
0 restraints	Absolute structure: Flack (1983), 3019 Friedel pairs
1 constraint	Flack parameter: 0.220 (12)

	x	y	z	Uiso*/Ueq
Nd1	0.22817 (5)	0.906931 (15)	0.75507 (4)	0.00599 (5)
Nd2	0.14522 (4)	0.574954 (15)	0.34489 (4)	0.00563 (5)
Nd3	0.71953 (5)	0.881350 (15)	0.74678 (4)	0.00533 (5)
Nd4	0.64866 (4)	0.612953 (17)	0.28408 (4)	0.00796 (5)
Ti1	0.47020 (19)	0.87935 (5)	0.25800 (16)	0.00463 (15)
Ti2	0.41480 (19)	0.67491 (5)	0.78904 (13)	0.00476 (16)
Ti3	0.96662 (19)	0.88160 (5)	0.25934 (16)	0.00437 (15)
Ti4	0.92426 (19)	0.67911 (5)	0.78238 (14)	0.00521 (16)
O1	0.5306 (4)	0.9810 (2)	0.5246 (6)	0.0050 (6)*
O2	0.5001 (5)	0.7695 (3)	0.4494 (7)	0.0081 (6)*
O3	0.4073 (5)	0.5586 (2)	0.5773 (6)	0.0064 (5)*
O4	0.2248 (6)	0.8923 (2)	0.3081 (6)	0.0099 (5)*
O5	0.1746 (6)	0.6954 (2)	0.6923 (6)	0.0072 (5)*
O6	0.4338 (5)	0.8188 (2)	0.9387 (6)	0.0044 (5)*
O7	0.3756 (5)	0.6078 (3)	0.0680 (7)	0.0114 (7)*
O8	0.9591 (5)	0.9796 (3)	0.5265 (6)	0.0079 (6)*
O9	0.8867 (5)	0.7715 (3)	0.4553 (7)	0.0073 (6)*
O10	0.8731 (5)	0.5702 (2)	0.5633 (6)	0.0065 (5)*
O11	0.7275 (6)	0.9089 (2)	0.1730 (6)	0.0062 (5)*
O12	0.6740 (6)	0.6933 (2)	0.8421 (6)	0.0084 (5)*
O13	0.9747 (5)	0.8155 (2)	0.9432 (6)	0.0072 (6)*
O14	0.9226 (5)	0.5940 (2)	0.0518 (6)	0.0063 (6)*

	U11	U22	U33	U12	U13	U23
Nd1	0.00488 (8)	0.00601 (7)	0.00701 (8)	0.00062 (9)	−0.00008 (13)	0.00075 (7)
Nd2	0.00502 (8)	0.00630 (7)	0.00558 (8)	0.00087 (10)	−0.00014 (11)	−0.00051 (6)
Nd3	0.00446 (8)	0.00581 (7)	0.00580 (8)	0.00100 (9)	−0.00004 (12)	0.00079 (6)
Nd4	0.00543 (9)	0.01077 (8)	0.00800 (9)	0.00231 (10)	−0.00042 (12)	−0.00119 (6)
Ti1	0.0050 (3)	0.0047 (2)	0.0043 (2)	0.0010 (4)	0.0009 (7)	0.0001 (2)
Ti2	0.0042 (3)	0.0046 (2)	0.0052 (3)	−0.0002 (3)	0.0013 (6)	−0.00020 (18)
Ti3	0.0041 (3)	0.0049 (2)	0.0044 (2)	0.0014 (3)	0.0011 (7)	0.0000 (2)
Ti4	0.0055 (3)	0.0045 (2)	0.0056 (3)	0.0003 (4)	0.0013 (7)	−0.0005 (2)

Nd1—O1	2.691 (3)	Nd4—O9	2.710 (3)
Nd1—O1i	2.631 (3)	Nd4—O10	2.426 (4)
Nd1—O4	2.450 (3)	Nd4—O12vi	2.627 (3)
Nd1—O5	2.742 (3)	Nd4—O14	2.499 (4)
Nd1—O6	2.312 (4)	Ti1—O1	1.975 (3)
Nd1—O8ii	2.701 (4)	Ti1—O1vii	2.220 (3)
Nd1—O8i	2.659 (4)	Ti1—O2	1.812 (4)
Nd1—O11i	2.411 (3)	Ti1—O4	1.935 (5)
Nd1—O13ii	2.360 (4)	Ti1—O6vi	1.917 (3)
Nd2—O3	2.415 (4)	Ti1—O11	2.010 (4)
Nd2—O5	2.450 (3)	Ti2—O2	2.269 (4)
Nd2—O7	2.318 (4)	Ti2—O3	1.898 (3)
Nd2—O10ii	2.398 (4)	Ti2—O5	1.973 (4)
Nd2—O10iii	2.423 (3)	Ti2—O6	2.028 (3)
Nd2—O14ii	2.381 (4)	Ti2—O7v	1.760 (4)
Nd2—O14iv	2.457 (3)	Ti2—O12	1.989 (5)
Nd3—O1	2.410 (3)	Ti3—O4viii	1.984 (5)
Nd3—O2	2.621 (3)	Ti3—O8	1.944 (4)
Nd3—O4i	2.931 (3)	Ti3—O8ix	2.213 (3)
Nd3—O6	2.458 (4)	Ti3—O9	1.820 (4)
Nd3—O8	2.401 (3)	Ti3—O11	1.977 (4)
Nd3—O9	2.601 (4)	Ti3—O13vi	1.935 (3)
Nd3—O11v	2.355 (3)	Ti4—O5viii	1.964 (4)
Nd3—O12	2.474 (3)	Ti4—O9	2.196 (4)
Nd3—O13	2.494 (4)	Ti4—O10	1.851 (3)
Nd4—O2	2.636 (4)	Ti4—O12	1.984 (5)
Nd4—O3	2.472 (4)	Ti4—O13	1.965 (3)
Nd4—O3iii	2.481 (3)	Ti4—O14v	1.841 (3)
Nd4—O7	2.398 (4)
O1—Ti1—O1vii	84.56 (13)	O4viii—Ti3—O8	88.84 (15)
O1—Ti1—O2	93.27 (15)	O4viii—Ti3—O8ix	83.46 (13)
O1—Ti1—O4	88.45 (14)	O4viii—Ti3—O9	101.10 (15)
O1—Ti1—O6vi	162.01 (13)	O4viii—Ti3—O11	164.50 (12)
O1—Ti1—O11	85.18 (13)	O4viii—Ti3—O13vi	93.06 (16)
O1vii—Ti1—O2	172.96 (16)	O8—Ti3—O8ix	85.77 (14)
O1vii—Ti1—O4	83.65 (13)	O8—Ti3—O9	91.99 (16)
O1vii—Ti1—O6vi	78.18 (12)	O8—Ti3—O11	86.75 (14)
O1vii—Ti1—O11	80.38 (13)	O8—Ti3—O13vi	165.40 (14)
O2—Ti1—O4	103.01 (15)	O8ix—Ti3—O9	174.89 (17)
O2—Ti1—O6vi	103.26 (15)	O8ix—Ti3—O11	81.40 (13)
O2—Ti1—O11	92.78 (15)	O8ix—Ti3—O13vi	80.08 (13)
O4—Ti1—O6vi	94.59 (16)	O9—Ti3—O11	93.89 (15)
O4—Ti1—O11	163.29 (13)	O9—Ti3—O13vi	101.82 (15)
O6vi—Ti1—O11	86.97 (15)	O11—Ti3—O13vi	87.61 (16)
O2—Ti2—O3	84.58 (13)	O5viii—Ti4—O9	86.72 (14)
O2—Ti2—O5	84.71 (13)	O5viii—Ti4—O10	90.78 (16)
O2—Ti2—O6	81.60 (13)	O5viii—Ti4—O12	167.53 (13)
O2—Ti2—O7v	172.61 (17)	O5viii—Ti4—O13	87.47 (15)
O2—Ti2—O12	81.44 (14)	O5viii—Ti4—O14v	100.64 (16)
O3—Ti2—O5	91.46 (16)	O9—Ti4—O10	82.06 (14)
O3—Ti2—O6	166.09 (13)	O9—Ti4—O12	82.86 (14)
O3—Ti2—O7v	98.63 (15)	O9—Ti4—O13	83.96 (14)
O3—Ti2—O12	95.54 (16)	O9—Ti4—O14v	171.88 (16)
O5—Ti2—O6	85.68 (14)	O10—Ti4—O12	94.53 (16)
O5—Ti2—O7v	101.79 (17)	O10—Ti4—O13	165.99 (15)
O5—Ti2—O12	163.81 (12)	O10—Ti4—O14v	94.32 (14)
O6—Ti2—O7v	95.28 (15)	O12—Ti4—O13	84.64 (15)
O6—Ti2—O12	84.04 (14)	O12—Ti4—O14v	90.22 (16)
O7v—Ti2—O12	91.59 (17)	O13—Ti4—O14v	99.66 (14)