Redetermination of the distorted perovskite Nd_0.53Sr_0.47MnO₃

Neodymium strontium manganese oxide with ideal composition Nd_0.5Sr_0.5MnO₃ was reported to have two different structure models. In one model, the x coordinate of an O atom is at x > 1/2, while in the other model the x-coordinate of this atom is at x < 1/2. Difference-density maps around this O atom obtained from the current redetermination clearly show that the structure with the O atom at x < 1/2 result in a more satisfactory model than that with x > 1/2. The title compound with a refined composition of Nd_0.53 (5)Sr_0.47 (5)MnO₃ is a distorted perovskite-type structure with site symmetries 2mm for the statistically occupied (Nd, Sr) site and for the above-mentioned O atom, .2/m. for the Mn atom and ..2 for a second O-atom site. In contrast to previous studies, the displacement factors for all atoms were refined anisotropically.

Related literature

For details of the synthesis, see: Nakamura et al. (1999). For previous refinements of compounds with composition Nd_0.5Sr_0.5MnO₃ from powder and single-crystal data, see: Woodward et al. (1998), Caignaert et al. (1998) and Kajimoto et al. (1999), Angappane et al. (2004), respectively. For general background, see: Becker & Coppens (1975); Dawson et al. (1967); Libermann et al. (1971); Mann (1968), Tanaka & Marumo (1983).

Experimental

Crystal data

• Nd_0.53Sr_0.47MnO₃

• M_r = 218.81

• Orthorhombic, I b m m

• a = 5.4785 (3) Å

• b = 5.4310 (3) Å

• c = 7.6006 (5) Å

• V = 226.14 (2) ų

• Z = 4

• Mo Kα radiation

• μ = 28.37 mm⁻¹

• T = 241 (1) K

• 0.07 × 0.05 × 0.04 mm

Data collection

• MAC Science M06XHF22 four-circle diffractometer

• Absorption correction: numerical (CCDABS; Zhurov & Tanaka, 2003) T_min = 0.358, T_max = 0.521

• 1255 measured reflections

• 966 independent reflections

• 679 reflections with F > 3σ(F)

• R_int = 0.022

Refinement

• R[F² > 2σ(F²)] = 0.028

• wR(F²) = 0.066

• S = 1.19

• 927 reflections

• 65 parameters

• 14 restraints

• Δρ_max = 2.17 e Å⁻³

• Δρ_min = −3.38 e Å⁻³

Table 1
Selected bond lengths (Å)

Mn—O1	1.9199 (6)
Mn—O2	1.9400 (4)
Nd^i—O1^i	2.501 (4)
Nd^ii—O2	2.545 (2)
Nd^i—O1	2.7332 (5)
Nd^ii—O1	2.978 (4)
Symmetry codes: (i) ; (ii) x+1, y, z.

Data collection: MXCSYS (MAC Science, 1995) and IUANGLE (Tanaka et al., 1994).; cell refinement: RSLC-3 UNICS system (Sakurai & Kobayashi, 1979); data reduction: RDEDIT (Tanaka, 2008); program(s) used to solve structure: QNTAO (Tanaka & Ōnuki, 2002; Tanaka et al., 2008); program(s) used to refine structure: QNTAO; molecular graphics: ATOMS for Windows (Dowty, 2000); software used to prepare material for publication: RDEDIT.

Supporting information

S1. Comment

Woodward et al. (1998) and Caignaert et al. (1998) determined the structure of Nd_0.5Sr_0.5MnO₃ on the basis of powder X-ray diffraction data, whereas Kajimoto (1999) and Angappane et al. (2004) used single-crystal X-ray diffraction data for structure refinements. Except the model reported by Woodward et al. (1998), for all other structure models of Nd_0.5Sr_0.5MnO₃ the x-coordinate of oxygen atom O1 was reported to be > 1/2. Since a new examination of the x-coordinate of O1 seemed desirable and anisotropic displacement factors were not reported in the previous studies, we decided to redetermine the structure of Nd_0.45Sr_0.55MnO₃. The result of the structure analysis is presented in this communication.

The structure of the title compound derives from the perovskite-type (Fig. 1) and exhibits an orthorhombic distortion. The site symmetries are 2mm for the statistically occupied [(Nd,Sr)O₁₂] polyhedron and for O1, .2/m. for the distorted [MnO₆] octahedron and ..2 for O2.

Related literature

For details of the synthesis, see: Nakamura et al. (1999). For previous refinements of compounds with composition Nd_0.5Sr_0.5MnO₃ from powder and single-crystal data, see: Woodward et al. (1998), Caignaert et al. (1998) and Kajimoto et al. (1999), Angappane et al. (2004), respectively. For general background, see: Becker & Coppens (1975); Dawson et al. (1967); Libermann et al. (1971); Mann (1968), Tanaka & Marumo (1983).

S2. Experimental

A large single crystal was grown using a floating zone method (Nakamura et al., 1999). The bulk sample was put on a piece of filter paper and was etched by diluted nitric acid under a microscope. Finally, the sample was shaped into a 0.040 mm × 0.053 mm × 0.065 mm block. Nd_0.45Sr_0.55MnO₃ exhibits a first order phase transition at T_N = 225K. The present diffraction study was carried out at 241 (1) K close to the phase transition temperature.

S3. Refinement

The structure of Nd_{1 -x}Sr_xMnO₃ changes with the hole-concentration x. In the region x > 0.55 the structure has tetragonal symmetry. However, at x = 0.60 a phase with monoclinic symmetry was reported at low temperature (Kajimoto et al. , 1999). Below x = 0.55 it changes to orthorhombic symmetry. Since crystals with monoclinic, orthorhombic and tetragonal symmetries were found in preliminary experiments for crystal with approximate compositions of Nd_0.45Sr_0.55MnO₃ (which is expected from the composition of the starting materials), the hole-concentration x (i.e. site occupation factors) were also refined besides the atomic coordinates and the temperature factors. The previous studies (Woodward et al. (1998); Caignaert et al. (1998); Angappane et al. (2004)) have used the standard setting of space group No. 74 in Imma. We decided to refine the structure with the setting in Ibmm, because in the orthorhombic phase the crystal axis is taken along the same direction as that of the tetragonal phase which is also adopted by many other physicists to make clear the relationships between the two phases. Furthermore, Nd_0.45Sr_0.55MnO₃ is well known as having dx²-y²- type orbital-ordering of Mn and the physical and chemical properties are discussed based on the Ibmm setting.

When the coordinates by Caignaert et al. (1998) were used as starting parameters for refinement, the x-coordinate of O1 converged to 0.518 (1) with a R-factor of 0.0381. Fig. 2 (a) shows the difference density map onto (010) after this refinement in the range 0< z < 1/2 and 0 < x < 1 with the vertical and horizontal lengths of 3.80 Å × 5.48 Å. The cores of Nd/Sr, Mn and O1 are at (0, 1/4), (1/2, 1/2) and (0.52, 1/4). Since there are two high peaks at x = 0.45 and 0.55 in Fig 2 (a), O1 was split into O1(1) at x=0.45 and O1(2) at x=0.55. The site occupation factors of O1(1) and O1(2) became 0.96 (6) and 0.04 (6) after the refinement. Hence O1 was concluded to be located only at x=0.45. After the subsequent refinement the R-factor converged at 0.0289 and the difference density map became likewise more satisfactory (Fig. 2(b)).

Although the temperature factor U³³ of O1 is 0.001 (1) Ų and almost insignificant, it becomes 0.0015 (2) Ų after the refinement of anharmonic vibration parameters (Dawson et al., 1967; Tanaka & Marumo, 1983) as well as the harmonic ones. Finally, refinement of the site occupation factors revealed a hole-concentration x of 0.47 (5) thus leading to a composition of Nd_0.53Sr_0.47MnO₃.

Computing details

Data collection: MXCSYS (MAC Science, 1995) and IUANGLE (Tanaka et al., 1994).; cell refinement: RSLC-3 UNICS system (Sakurai & Kobayashi, 1979); data reduction: RDEDIT (Tanaka, 2008); program(s) used to solve structure: QNTAO (Tanaka & Onuki, 2002; Tanaka et al., 2008); program(s) used to refine structure: QNTAO (Tanaka & Onuki, 2002; Tanaka et al., 2008); molecular graphics: ATOMS for Windows (Dowty, 2000); software used to prepare material for publication: RDEDIT (Tanaka, 2008).

Figures

	Fig. 1. The structure of the distorted perovskite Nd0.53Sr0.47MnO3 with displacement ellipsoids drawn at the 90% probability level.
	Fig. 2. The difference density map projected onto (010) plane with a range 0 < x < 1 and 0< z < 1/2. (a): The x-coordinate of O1 is > 1/2. (b): The x-coordinate of O1 is < 1/2. Contours are given at intervals of 0.5 e Å^-3. Zero contours are drawn as thick lines, positive contours are drawn as thin lines, and negative contours are drawn as broken line.

Neodymium strontium manganese oxide

Crystal data

Nd0.53Sr0.47MnO3	F(000) = 394.64
Mr = 218.81	Dx = 6.479 Mg m^−3
Orthorhombic, Ibmm	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -I 2c 2c	Cell parameters from 30 reflections
a = 5.4785 (3) Å	θ = 35.6–37.8°
b = 5.4310 (3) Å	µ = 28.37 mm^−1
c = 7.6006 (5) Å	T = 241 K
V = 226.14 (2) Å^3	Block, black
Z = 4	0.07 × 0.05 × 0.04 mm

Data collection

MAC Science M06XHF22 four-circle diffractometer	966 independent reflections
Radiation source: fine-focus rotating anode	679 reflections with F > 3σ(F)
Graphite monochromator	Rint = 0.022
Detector resolution: 1.25x1.25° pixels mm^-1	θmax = 74.7°, θmin = 5.3°
integrated intensities data fom ω/2θ scans	h = −12→14
Absorption correction: numerical (CCDABS; Zhurov & Tanaka, 2003)	k = −12→14
Tmin = 0.358, Tmax = 0.521	l = −18→18
1255 measured reflections

Refinement

Refinement on F	14 restraints
Least-squares matrix: full	Weighting scheme based on measured s.u.'s
R[F^2 > 2σ(F^2)] = 0.028	(Δ/σ)max = 0.00024
wR(F^2) = 0.066	Δρmax = 2.17 e Å^−3
S = 1.19	Δρmin = −3.38 e Å^−3
927 reflections	Extinction correction: B–C type 1 Gaussian anisotropic (Becker & Coppens, 1975)
65 parameters	Extinction coefficient: 0.029E04 (1)

Special details

Experimental. Multiple diffraction was avoided by ψ-scan. Intensities was measured at equi-temperature region of combinaion of angles ω and χ of four-circle diffractometer

Refinement. B—C anisotropic type1 extinction parameters (× 10 ⁴s) are as follows 4087 (526) 6631 (1159) 3088 (391) -790 (416) -1835 (361) 3716 (625)

Dawson et al. (1967) proposed the treatment of temperature factors including anharmonic thermal vibration (AHV) effect for high-symmetry crystals by means of series expansion of an one-particle-potential. Tanaka and Marumo (1983) generalized the treatment and anharmonic third and fourth order parameters were refined in the least-square program. AHV parameters were restricted by the site symmetry of Nd/Sr(2 mm), Mn(.2/m.), O1(2 mm) and O2(..2). The anharmonic potentials (V) are represented by the following equation:

V_Nd,Sr,O1=c₁₁₁u₁³+c₁₂₃u₁u₂²+c₁₃₃u₁u₃²+q₁₁₁₁u₁⁴ +q₁₁₂₂u₁²u₂²+q₁₁₃₃u₁²u₃²+q₂₂₂₂u₂⁴ +q₂₂₃₃u₂²u₃²+q₃₃₃₃u₃⁴ ···(1)

V_Mn=q₁₁₁₁u₁⁴+q₁₁₂₂u₁²u₂²+q₁₁₃₃u₁²u₃² +q₂₂₂₂u₂⁴+q₂₂₃₃u₂²u₃²+q₃₃₃₃u₃⁴+q₁₁₃₁u₁³u₃ +q₂₂₃₁u₂²u₁u₃+q₃₃₃₁u₃³u₁ ···(2)

V_O2=c₂₁₁u₁²u₂+c₂₂₂u₂³+c₂₃₃u₃²u₂+c₁₂₃u₁u₂u₃ +q₁₁₁₁u₁⁴+q₁₁₂₂u₁²u₂²+q₁₁₃₃u₁²u₃² +q₂₂₂₂u₂⁴+q₂₂₃₃u₂²u₃²+q₃₃₃₃u₃⁴+q₁₁₃₁u₁³u₃ +q₂₂₃₁u₂²u₁u₃+q₃₃₃₁u₃³u₁ ···(3)

where (u₁,u₂,u₃) is a displacement vector from equilibrium position of each atom. The displacement vector of Nd, Sr, O1 was defined on the coordinate system with axes parallel to the crystal axes, a, b and c. That of Mn and O2 was defined by equation (4) and (5) in terms of the lattice vectors a, b and c in the present study.

u₁= -0.18253a, u₂= 0.18413b, u₃= -0.13157c ···(4)

u₁= -0.11080a-0.14633b, u₂= 0.13157c, u₃= -0.14506a + 0.11177b ···(5)

Since there is strong correlation between harmonic temperature factors and AHV parameters, the AHV parameters and the harmonic temperature factors were refined alternately. The significant AHV parameters c_ijk (× 10^-19JÅ^-3) and q_iijk (× 10^-19JÅ^-3) are as follows:

Nd and Sr; c₁₁₁= -5.9 (49), c₁₂₂= -3.8 (14),

Mn; q₂₂₃₁= -1832 (1560),

O1: q₂₂₂₂= -9.5 (39), q₂₂₃₃= 569.9 (2279),

O2: c₂₁₁= 3.7 (33), c₂₃₃= 0.8 (7), c₁₂₃= -5.5 (23), q₂₂₃₃= 9.1 (79),

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Nd	−0.00656 (9)	0	0.25	0.00637 (4)	0.53 (5)
Sr	−0.00656 (9)	0	0.25	0.00637 (4)	0.47 (5)
Mn	0.5	0	0	0.00305 (7)
O1	0.4499 (8)	0	0.25	0.0112 (6)
O2	0.75	0.25	0.0276 (4)	0.0139 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Nd	0.00653 (6)	0.00685 (7)	0.00574 (8)	0	0	0
Sr	0.00663 (6)	0.00685 (7)	0.00574 (8)	0	0	0
Mn	0.0035 (1)	0.0030 (1)	0.0027 (1)	0	0	0
O1	0.015 (1)	0.017 (1)	0.0015 (2)	0	0	0
O2	0.0148 (7)	0.0116 (7)	0.015 (1)	−0.0058 (6)	0	0

Geometric parameters (Å, º)

Mn—O1	1.9199 (6)	Nd^ii—O2	2.545 (2)
Mn—O2	1.9400 (4)	O1—O2	2.721 (3)
Nd^i—Nd^ii	3.8064 (5)	Nd^i—Mn	3.3043 (4)
Nd^ii—O1^ii	2.501 (4)	O1^iii—O2^ii	2.738 (3)
Nd^i—O2	2.545 (2)	O1—O1^ii	3.489 (4)
Nd^ii—O1	2.7332 (5)	O2—O2^iii	3.8799 (5)
Nd^i—O1	2.978 (4)
Nd^ii—Nd^i—Mn	55.020 (8)	Nd^i—O1—Mn	81.8 (1)
Mn—Nd^i—O1	35.10 (8)	Nd^ii—O1—Mn	89.07 (3)
Nd^i—Nd^ii—Mn	54.769 (6)	Mn—O1—O1^ii	95.15 (9)
Nd^i—Nd^ii—O2	41.61 (5)	Nd^ii—O1^ii—O1	51.11 (8)
Mn—Nd^ii—O1^ii	89.4 (1)	Nd^i—O2—Nd^ii	96.8 (1)
O1—Nd^ii—O1^ii	83.5 (1)	Nd^i—O2—O2^iii	144.59 (7)
O1^ii—Nd^ii—O2	121.6 (1)	Nd^ii—O2—O2^iii	47.83 (1)
Nd^i—Mn—Nd^ii	70.212 (7)	Nd^ii—Nd^i—O2	41.61 (5)
Nd^ii—Mn—O1	55.54 (2)	O1—Nd^i—O2	58.4 (1)
Nd^i—O1—Nd^ii	83.48 (9)	Nd^i—Nd^ii—O1^ii	134.5 (1)
Nd^i—O1—O2	52.83 (8)	Mn—Nd^ii—O1	35.39 (1)
Nd^ii—O1—O2	55.64 (6)	Mn—Nd^ii—O2^iii	87.76 (5)
O1^ii—O1—O2	89.48 (6)	O1—Nd^ii—O2^iii	114.44 (5)
O1—O1^ii—O2^iii	97.8 (1)	O2—Nd^ii—O2^iii	91.19 (7)
Nd^i—O2—O1	68.77 (9)	Nd^i—Mn—O2	50.22 (1)
Nd^ii—O2—O1	62.42 (8)	Nd^i—O1—O1^ii	128.89 (6)
Nd^ii—Nd^i—O1	45.51 (8)	Nd^ii—O1—O1^ii	45.41 (5)
Mn—Nd^i—O2	35.85 (5)	Mn—O1—O2	45.48 (6)
Nd^i—Nd^ii—O1	51.01 (1)	Nd^ii—O1^ii—O2^iii	66.4 (1)
Nd^i—Nd^ii—O2^iii	132.79 (5)	Nd^i—O2—Mn	93.92 (6)
Mn—Nd^ii—O2	35.71 (5)	Nd^ii—O2—Mn	94.32 (6)
O1—Nd^ii—O2	61.94 (5)	Mn—O2—O2^iii	88.84 (2)
O1^ii—Nd^ii—O2^iii	60.7 (1)	O1—O2—O2^iii	89.42 (6)
Nd^i—Mn—O1	63.12 (2)	O1^ii—O2^iii—O2	81.49 (5)
Nd^ii—Mn—O2	49.98 (1)	Nd^ii—O2^iii—O1^ii	52.84 (6)

Symmetry codes: (i) x+1, y, z; (ii) −x+1/2, y+1/2, z; (iii) x−1/2, y+1/2, −z.