Original disorder-order transition related to electronic and magnetic properties in the thermoelectric misfit phase [Ca₂CoO₃][CoO₂]_1.62

A structural phase transition is shown around 400 K for the thermoelectric lamellar misfit cobalt oxide [Ca₂CoO₃][CoO₂]_1.62. This transition is related to a rearrangement of the central [CoO] layer of the [Ca₂CoO₃] slab of this structure, characterized by a commensurate intrinsic modulation q₂ = a^* - c^*. The partial residual disorder related to split Co and O atomic sites along the misfit b direction disappears and one can describe this layer with its triple chains as a modulated configuration with a regular and not distorted periodicity along b. This phase transition is associated with small changes observed in the transport and magnetic properties as a function of temperature.

Computing details

Program(s) used to refine structure: Jana2000 (Petricek, Dusek & Palatinus, 2000); software used to prepare material for publication: Jana2000 (Petricek, Dusek & Palatinus, 2000).

(I)

Crystal data

Ca2Co2.511O6.138	V = 236.83 Å^3
Mr = 326.3	Z = 2
Monoclinic, X2/m†	F(000) = 314
q1 = 0.66667a* + -0.33333c*; q2 = 1.62500b*‡	Dx = 4.575 Mg m^−3
a = 4.839 Å	Mo Kα radiation, λ = 0.71069 Å
b = 4.553 Å	µ = 10.85 mm^−1
c = 10.858 Å	T = 293 K
β = 98.12°

† Symmetry operations: (1) x₁, x₂, x₃, x₄, x₅; (2) −x₁, x₂, −x₃, −x₄, 1/2+x₅; (3) −x₁, −x₂, −x₃, −x₄, −x₅; (4) x₁, −x₂, x₃, x₄, 1/2−x₅; (5) 1/2+x₁, 1/2+x₂, x₃, x₄, 1/2+x₅; (6) 1/2−x₁, 1/2+x₂, −x₃, −x₄, x₅; (7) 1/2−x₁, 1/2−x₂, −x₃, −x₄, 1/2−x₅; (8) 1/2+x₁, 1/2−x₂, x₃, x₄, −x₅.

‡ ;

Data collection

2014 measured reflections	θmax = 32.1°, θmin = 5.8°
2014 independent reflections	h = −7→7
841 reflections with I > 3σ(I)	k = 0→6
Rint = 0.000	l = 0→16

Refinement

Refinement on F	76 parameters
R[F^2 > 2σ(F^2)] = 0.034	Weighting scheme based on measured s.u.'s w = 1/σ^2(F)
wR(F^2) = 0.025	(Δ/σ)max = 0.015
S = 1.76	Δρmax = 1.97 e Å^−3
2014 reflections	Δρmin = −2.40 e Å^−3

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ca	0.43024 (7)	0	0.27564 (3)	0.01225 (12)
O1	0.0529 (2)	0	0.66415 (10)	0.0142 (4)
Co1a	0	0	0.5	0.0103 (11)*	0.2593
Co1b	0.0686 (14)	0	0.5001 (4)	0.0317 (6)	0.354
O2a	0.0672 (17)	0.5	0.5003 (3)	0.0284 (17)	0.4835
Co2	0.75	0.75	0	0.00545 (10)	0.9498
O3	0.3861 (2)	0.75	−0.09310 (9)	0.0089 (3)	0.9757

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca	0.0113 (2)	0.0135 (2)	0.0117 (2)	0	0.00090 (15)	0
O1	0.0167 (7)	0.0162 (7)	0.0097 (7)	0	0.0017 (5)	0
Co1b	0.0195 (12)	0.0723 (11)	0.0032 (6)	0	0.0015 (6)	0
O2a	0.005 (4)	0.068 (2)	0.0111 (13)	0	0	0
Co2	0.00421 (15)	0.0062 (2)	0.00588 (14)	0	0.00061 (10)	0
O3	0.0063 (5)	0.0098 (8)	0.0105 (5)	0	0.0008 (4)	0

Geometric parameters (Å, º)

	Average	Minimum	Maximum
Ca—O1^i	2.516 (6)	2.422 (8)	2.626 (8)
Ca—O1^ii	2.495 (5)	2.410 (7)	2.587 (7)
Ca—O3^iii	59.29 (7)	2.255 (4)	2.882 (3)
Ca—O3^iv	78.50 (7)	2.427 (3)	4.200 (4)
Ca—O11^ii	2.3675 (16)	2.3553 (19)	2.3831 (12)
Ca—O11^v	2.3675 (16)	2.3553 (19)	2.3831 (12)
Ca—O31^iii	74.00 (5)	2.3532 (16)	3.945 (4)
Ca—O31^iv	62.42 (5)	2.2919 (18)	3.1979 (15)
Co2—O3	1.903 (4)	1.894 (4)	1.913 (4)
Co2—O3^iii	1.899 (2)	1.891 (3)	1.908 (2)
Co2—O3^iv	1.899 (2)	1.891 (3)	1.908 (2)
Co2—O31^vi	1.8994 (16)	1.890 (3)	1.908 (2)
Co2—O31	1.8994 (16)	1.890 (3)	1.908 (2)
Co2—O31^vii	1.9025 (19)	1.8939 (15)	1.913 (3)
Ca1—O1^ii	2.368 (3)	2.355 (3)	2.384 (3)
Ca1—O1^v	2.368 (3)	2.355 (3)	2.384 (3)
Ca1—O3^iii	88.35 (6)	2.759 (3)	4.6684 (18)
Ca1—O3^iv	59.09 (7)	2.312 (2)	2.631 (3)
Ca1—O3^viii	88.42 (6)	2.746 (3)	4.638 (2)
Ca1—O11^v	2.516 (4)	2.427 (4)	2.622 (7)
Ca1—O11^ix	2.495 (4)	2.414 (4)	2.583 (5)
Ca1—O31^vii	66.52 (5)	2.290 (2)	3.537 (3)
Ca1—O31^x	66.49 (5)	2.269 (2)	3.5180 (17)
O1^i—Ca—O1^ii	150.1 (2)	145.4 (3)	152.9 (3)
O1^i—Ca—O11^ii	85.7 (2)	83.34 (19)	88.8 (2)
O1^i—Ca—O11^v	85.7 (2)	83.34 (19)	88.8 (2)
O1^ii—Ca—O1^i	150.1 (2)	145.4 (3)	152.9 (3)
O1^ii—Ca—O11^ii	86.19 (19)	83.88 (18)	88.90 (18)
O1^ii—Ca—O11^v	86.19 (19)	83.88 (18)	88.90 (18)
O3^iii—Ca—O11^ii	91.9 (2)	66.59 (19)	121.5 (2)
O3^iii—Ca—O11^v	115.4 (2)	85.9 (2)	142.4 (2)
O3^iv—Ca—O11^ii	146.1 (2)	128.7 (2)	159.8 (2)
O3^iv—Ca—O11^v	61.0 (2)	46.54 (19)	80.1 (2)
O11^ii—Ca—O11^v	148.1 (2)	147.5 (2)	148.7 (2)
O11^v—Ca—O11^ii	148.1 (2)	147.5 (2)	148.7 (2)
O3—Co2—O3^iii	85.31 (10)	84.01 (10)	86.60 (10)
O3—Co2—O3^iv	85.31 (10)	84.01 (10)	86.60 (10)
O3—Co2—O31^vi	94.69 (10)	92.77 (11)	96.45 (10)
O3—Co2—O31	94.69 (10)	92.77 (11)	96.45 (10)
O3—Co2—O31^vii	179.38 (11)	178.67 (14)	179.91 (10)
O3^iii—Co2—O3	85.31 (13)	84.01 (11)	86.60 (13)
O3^iii—Co2—O3^iv	95.08 (11)	93.83 (10)	96.34 (12)
O3^iii—Co2—O31^vi	84.91 (10)	84.84 (10)	85.01 (10)
O3^iii—Co2—O31	178.62 (10)	177.52 (11)	179.75 (9)
O3^iii—Co2—O31^vii	94.69 (13)	92.73 (11)	96.41 (12)
O3^iv—Co2—O3	85.31 (13)	84.01 (11)	86.60 (13)
O3^iv—Co2—O3^iii	95.08 (11)	93.83 (10)	96.34 (12)
O3^iv—Co2—O31^vi	178.62 (10)	177.52 (11)	179.75 (9)
O3^iv—Co2—O31	84.91 (10)	84.84 (10)	85.01 (10)
O3^iv—Co2—O31^vii	94.69 (13)	92.73 (11)	96.41 (12)
O31^vi—Co2—O31	95.08 (9)	93.79 (9)	96.31 (11)
O31^vi—Co2—O31^vii	85.31 (9)	84.01 (8)	86.59 (11)
O31—Co2—O31^vi	95.08 (9)	93.79 (9)	96.31 (12)
O31—Co2—O31^vii	85.31 (9)	84.01 (8)	86.59 (11)
O31^vii—Co2—O31^vi	85.31 (9)	84.01 (10)	86.59 (10)
O31^vii—Co2—O31	85.31 (9)	84.01 (10)	86.59 (10)
O1^ii—Ca1—O1^v	148.1 (2)	147.6 (2)	148.7 (2)
O1^ii—Ca1—O11^v	85.72 (14)	83.20 (13)	88.92 (14)
O1^ii—Ca1—O11^ix	86.19 (13)	83.94 (9)	88.87 (10)
O1^v—Ca1—O1^ii	148.1 (2)	147.6 (2)	148.7 (2)
O1^v—Ca1—O11^v	85.72 (14)	83.20 (13)	88.92 (14)
O1^v—Ca1—O11^ix	86.19 (13)	83.94 (9)	88.87 (10)
O3^iii—Ca1—O11^v	78.57 (13)	74.96 (16)	82.82 (10)
O3^iii—Ca1—O11^ix	118.86 (12)	110.65 (10)	127.77 (15)
O3^iv—Ca1—O11^v	73.22 (18)	69.22 (19)	77.24 (17)
O3^iv—Ca1—O11^ix	134.8 (2)	127.24 (18)	142.4 (2)
O3^viii—Ca1—O11^v	78.56 (13)	75.14 (15)	83.17 (9)
O3^viii—Ca1—O11^ix	118.87 (12)	109.99 (9)	127.37 (14)
O11^v—Ca1—O11^ix	150.1 (2)	145.4 (2)	152.8 (2)
O11^ix—Ca1—O11^v	150.1 (2)	145.4 (2)	152.8 (2)

Symmetry codes: (i) −x₁, −x₂, −x₃+1, −x₄, −x₅; (ii) −x₁+1, −x₂, −x₃+1, −x₄, −x₅; (iii) −x₁+1, −x₂+1, −x₃, −x₄, −x₅; (iv) −x₁+1, −x₂+2, −x₃, −x₄, −x₅; (v) −x₁+1, −x₂+1, −x₃+1, −x₄, −x₅; (vi) x₁, x₂−1, x₃, x₄, x₅; (vii) −x₁+2, −x₂+2, −x₃, −x₄, −x₅; (viii) −x₁+1, −x₂+3, −x₃, −x₄, −x₅; (ix) −x₁+2, −x₂+1, −x₃+1, −x₄, −x₅; (x) −x₁+2, −x₂+3, −x₃, −x₄, −x₅.