Crystal structure and magnetic properties of LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2.

The synthesis, structure, and magnetic properties of lithium dibarium calcium oxide fluoride di-sulfide are reported. LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2 crystallizes in the tetra-gonal space group P4/nmm. The structure exhibits disorder of the Ca(2+) and Bi(3+) cations, and the O(2-) and F(-) anions. The structure is composed of a stacking of [(O,F)2La2] layers and double [(Bi,Ca)S2] layers. Magnetic property measurements indicate a very small magnetization at 300 K and the existence of weak ferromagnetism at 2 K.

Chemical context

Layered crystal structures seem to be a common stage on which to explore superconductivity (Vershinin et al., 2004 ▸; Kamihara et al., 2008 ▸; Chen et al., 2008 ▸; Fang et al., 2010 ▸). The discovery of [Fe2 An 2] (An = P, As, S, Se or Te) and [CuO2] superconducting layers has opened a new field in physics and chemistry for the exploration of low-dimensional superconductivity. Recently, superconductivity with transition temperatures of 4.5 K was reported in the BiS2-based compound Bi4O4S3 (Singh et al., 2012 ▸). Soon after, LnO1-FBiS2 (Ln = La, Ce, Pr and Nd), were reported to be superconducting with transition temperatures T c of 3–10.6 K (Nagao et al., 2013 ▸; Demura et al., 2013 ▸). The mother BiS2-based layered compound AeFBiS2 (Ae = Ca, Sr or Ba; Lei et al., 2013 ▸; Han et al., 2008 ▸) is isostructural to LnOBiS2, with the [Ln 2O2]2− layer being replaced by an isocharged [Sr2F2]2− block. The parent phase of SrFBiS2 shows semiconducting behavior, but electron-doped Sr0.5La0.5FBiS2 has a superconducting transition of 2.8 K (Lin et al., 2013 ▸). Herein the synthesis, structure and magnetic properties of LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2 are reported.

Structural commentary

We attempted to prepare the Ca and F double-doped compound La1−CaO1−2F2BiS2, but the results indicate the single-crystal composition is LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2. An SEM image shows thick plate-shaped crystals of LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2 (Fig. 1 ▸). LaO1−FBiS2 crystals usually show a thin-sheet shape (Fig. 2 ▸). From the EDXS analysis, we obtained the elemental components of La, Ca, Bi, S, F and O. The final composition was obtained by structure refinement (details can be seen in the Refinement section).

Figure 1

SEM image of LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2.

Figure 2

SEM image of LaO0.6F0.4BiS2.

The structure of LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2, shown in Fig. 3 ▸, is composed of a stacking of [(O,F)2La2] layers and double [(Bi,Ca)S2] layers as in LaO1−FBiS2. The double [(Bi,Ca)S2] layers show Bi1/Ca1—S2 distances of 2.8672 (6) Å representing equatorial bonds and Bi1/Ca1—S1 distances of 2.530 (3) Å representing axial bonds; these are a little shorter than the Bi1—S1 distance of 2.87476 (15) and Bi1—S2 distance of 2.530 (6) Å in LaO1−FBiS2. The [(O,F)2La2] layers exhibit O1/F1—La1 bond lengths of 2.4414 (6) Å and La1—O1/F1—La1 bond angles of 108.08 (2) and 112.29 (4)°, which are close to the La—O/F bond length of 2.4402 (8) Å and La1—O1/F1—La1 bond angles of 107.82 (3) and 112.82 (6)° in LaO1−FBiS2. The ionic radius of Ca2+ is 114 pm which is a little shorter than that of 117.2/117 pm for La3+/Bi3+. The distinct reduced Bi1/Ca1—S2 distances in the title compound reflect the fact that Ca substitutes Bi sites rather than La sites.

Figure 3

Crystal structure of LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2, showing [(O,F)2La2] layers and double [BiS2] layers (O/F in red, La in blue, Bi/Ca in pink and S in yellow; 50% probability ellipsoids).

Magnetic property measurements

The magnetization versus temperature under a 1 T field for the title compound is given in Fig. 4 ▸. Magnetization versus magnetic field is given in Fig. 5 ▸ for fields ranging from −5 to 5 T at 2 K and 300 K. The magnetic properties indicate weak ferromagnetism at 2 K and a very low magnetization at 300 K. The superconducting transition is not observed in the measured temperature range. This might be related to the Ca substitution of the Bi site in the title compound. For superconducting LaO1−FBiS2 crystals, the density of states at the Fermi level is mainly directed by the Bi p orbital. [BiS2] layers play a vital role in the transport and superconducting properties. The Ca substitution of the Bi site leads to a hole doping which changed the electronic band structure and density of state of LaO1−FBiS2. Another reason might be the reduced F content in LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2 compared with LaO1−FBiS2.

Figure 4

Magnetic moment versus temperature for LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2 under a 1 T field.

Figure 5

Magnetic moment versus field for LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2 from −5 T to 5 T at 2 K and 300 K.

Database survey

LnO1−FBiS2 (Ln = La, Ce, Pr and Nd) compounds were reported by Nagao et al. (2013 ▸) and Demura et al. (2013 ▸). AeFBiS2 (Ae = Ca, Sr, Ba) (Lei et al., 2013 ▸; Han et al., 2008 ▸) are isostructural to LnOBiS2. The doped Sr0.5La0.5FBiS2 (Lin et al., 2013 ▸) is isostructural to AeFBiS2.

Synthesis and crystallization

LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2 was prepared using of Bi2O3, CaF2, La2S3, Bi2S3 and Bi raw materials. The mixtures with a nominal composition of La0.85Ca0.15O0.70F0.30BiS2 were ground, pressed into pellets, sealed in an evacuated quartz tube, and heated at 1073 K for 3 d. High-quality single crystals were grown by using KI as the flux. Nominal La0.85Ca0.15O0.70F0.30BiS2 and KI in the molar ratio of 1:3 were mixed and placed in a quartz tube, which was sealed and heated to 1273 K and kept at this temperature for 1 d, then cooled to room temperature in 10 d. The product was washed with distilled water and acetone, then dried at 353 K for 12 h; finally black plate-shaped crystals were obtained.

The morphology and element compositions were investigated by a scanning electronic microscope equipped with an energy dispersive X-ray spectroscopy (EDXS, Oxford Instruments). The EDXS shows the atom % ratio for S:Ca:La:Bi to be 48.23: 6.94: 24.36: 20.48. O and F could not be determined precisely. Magnetic properties were measured on a multifunctional physical properties measurement system (PPMS, Quantum Design).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▸. The La, Bi, S and O atoms were located in difference maps and their positions were freely refined. Ca was assumed at La sites at first, but the refinement show no reducing occupancy of La. The partial occupancy of Bi indicates a mixed occupancy with Ca. Ca and Bi were refined together later. EDXS measurements could not determine occupancies of O and F precisely. If the occupancies of F and O are refined together, the obtained composition is La2Bi1.859 (4)Ca0.141 (4)O0.48 (14)F0.52 (14)S4 with high standard errors for O and F. In order to keep charge neutrality, the occupancy of F was fixed to be the same as Ca so the final composition of LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2 was obtained.

Table 1

Experimental details

Crystal data
Chemical formula	LaCa0.143 (4)O0.857 (4)F0.143 (4)Bi0.857 (4)S2
M r	404.26
Crystal system, space group	Tetragonal, P4/n m m
Temperature (K)	300
a, c (Å)	4.0548 (9), 13.370 (3)
V (Å3)	219.82 (11)
Z	2
Radiation type	Mo Kα
μ (mm−1)	44.78
Crystal size (mm)	0.05 × 0.05 × 0.02
Data collection
Diffractometer	Bruker D8 Quest
Absorption correction	Multi-scan (SADABS; Bruker, 2001 ▸)
T min, T max	0.154, 0.511
No. of measured, independent and observed [I > 2σ(I)] reflections	3493, 191, 190
R int	0.046
(sin θ/λ)max (Å−1)	0.648
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.020, 0.052, 1.31
No. of reflections	191
No. of parameters	17
Δρmax, Δρmin (e Å−3)	1.48, −1.53

Computer programs: APEX2 and SAINT (Bruker, 2004 ▸), SHELXS (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick 2015 ▸), DIAMOND (Brandenburg, 2004 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I, New_Global_Publ_Block. DOI: 10.1107/S2056989016008082/pj2030sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016008082/pj2030Isup2.hkl

CCDC reference: 1480636

Additional supporting information: crystallographic information; 3D view; checkCIF report

Bi0.857Ca0.143F0.143LaO0.857S2	Dx = 6.108 Mg m−3
Mr = 404.26	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P4/nmm	Cell parameters from 189 reflections
a = 4.0548 (9) Å	θ = 4.6–27.4°
c = 13.370 (3) Å	µ = 44.78 mm−1
V = 219.82 (11) Å3	T = 300 K
Z = 2	Block, blue
F(000) = 342.3	0.05 × 0.05 × 0.02 mm

Bruker D8 Quest diffractometer	Rint = 0.046
Radiation source: fine-focus sealed tube	θmax = 27.4°, θmin = 4.6°
Profile fitted 2θ/ω scans (Clegg, 1981)	h = −5→5
Absorption correction: multi-scan (SADABS; Bruker, 2001)	k = −5→4
Tmin = 0.154, Tmax = 0.511	l = −17→17
3493 measured reflections	3 standard reflections every 90 reflections
191 independent reflections	intensity decay: none
190 reflections with I > 2σ(I)

Refinement on F2	Primary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ2(Fo2) + (0.0318P)2 + 0.5025P] where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.020	(Δ/σ)max < 0.001
wR(F2) = 0.052	Δρmax = 1.48 e Å−3
S = 1.31	Δρmin = −1.53 e Å−3
191 reflections	Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
17 parameters	Extinction coefficient: 0.033 (3)
0 restraints

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

	x	y	z	Uiso*/Ueq	Occ. (<1)
La1	0.7500	0.7500	0.89827 (6)	0.0127 (3)
Ca1	0.2500	0.2500	0.62178 (4)	0.0126 (3)	0.143 (4)
Bi1	0.2500	0.2500	0.62178 (4)	0.0126 (3)	0.857 (4)
F1	0.7500	0.2500	1.0000	0.0079 (14)	0.143 (4)
O1	0.7500	0.2500	1.0000	0.0079 (14)	0.857 (4)
S1	0.2500	0.2500	0.8110 (2)	0.0104 (6)
S2	0.7500	0.7500	0.6221 (3)	0.0236 (8)

	U11	U22	U33	U12	U13	U23
La1	0.0115 (4)	0.0115 (4)	0.0151 (5)	0.000	0.000	0.000
Ca1	0.0146 (3)	0.0146 (3)	0.0087 (3)	0.000	0.000	0.000
Bi1	0.0146 (3)	0.0146 (3)	0.0087 (3)	0.000	0.000	0.000
F1	0.0087 (18)	0.0087 (18)	0.006 (3)	0.000	0.000	0.000
O1	0.0087 (18)	0.0087 (18)	0.006 (3)	0.000	0.000	0.000
S1	0.0101 (7)	0.0101 (7)	0.0109 (12)	0.000	0.000	0.000
S2	0.0200 (10)	0.0200 (10)	0.0306 (18)	0.000	0.000	0.000

La1—O1i	2.4414 (6)	Ca1—Ca1v	4.0548 (9)
La1—O1ii	2.4414 (6)	Ca1—Ca1viii	4.0548 (9)
La1—F1i	2.4414 (6)	Ca1—Bi1ii	4.0548 (9)
La1—F1ii	2.4414 (6)	Ca1—Bi1viii	4.0548 (9)
La1—F1	2.4414 (6)	F1—La1i	2.4414 (6)
La1—O1iii	2.4414 (6)	F1—La1viii	2.4414 (6)
La1—O1	2.4414 (6)	F1—La1iii	2.4414 (6)
La1—F1iii	2.4414 (6)	O1—La1i	2.4414 (6)
La1—S1	3.0954 (13)	O1—La1viii	2.4414 (6)
La1—S1iv	3.0954 (13)	O1—La1iii	2.4414 (6)
La1—S1ii	3.0954 (13)	S1—La1vi	3.0954 (13)
La1—S1v	3.0954 (13)	S1—La1vii	3.0954 (13)
Ca1—S1	2.530 (3)	S1—La1viii	3.0954 (13)
Ca1—S2	2.8672 (6)	S2—Bi1iv	2.8672 (6)
Ca1—S2vi	2.8672 (6)	S2—Ca1iv	2.8672 (6)
Ca1—S2vii	2.8672 (6)	S2—Ca1v	2.8672 (6)
Ca1—S2viii	2.8672 (6)	S2—Ca1ii	2.8672 (6)
Ca1—S2ix	3.261 (4)	S2—Bi1ii	2.8672 (6)
Ca1—Ca1ii	4.0548 (9)	S2—Bi1v	2.8672 (6)
Ca1—Ca1vii	4.0548 (9)	S2—Ca1ix	3.261 (4)
O1i—La1—O1ii	71.917 (18)	S2viii—Ca1—Ca1vii	135.0
O1i—La1—F1i	0.0	S2ix—Ca1—Ca1vii	90.0
O1ii—La1—F1i	71.917 (18)	Ca1ii—Ca1—Ca1vii	90.0
O1i—La1—F1ii	71.917 (18)	S1—Ca1—Ca1v	90.0
O1ii—La1—F1ii	0.0	S2—Ca1—Ca1v	45.0
F1i—La1—F1ii	71.917 (18)	S2vi—Ca1—Ca1v	135.0
O1i—La1—F1	71.917 (18)	S2vii—Ca1—Ca1v	135.0
O1ii—La1—F1	112.29 (4)	S2viii—Ca1—Ca1v	45.0
F1i—La1—F1	71.917 (18)	S2ix—Ca1—Ca1v	90.0
F1ii—La1—F1	112.29 (4)	Ca1ii—Ca1—Ca1v	90.0
O1i—La1—O1iii	112.29 (4)	Ca1vii—Ca1—Ca1v	180.0
O1ii—La1—O1iii	71.917 (18)	S1—Ca1—Ca1viii	90.0
F1i—La1—O1iii	112.29 (4)	S2—Ca1—Ca1viii	135.0
F1ii—La1—O1iii	71.917 (18)	S2vi—Ca1—Ca1viii	45.0
F1—La1—O1iii	71.917 (18)	S2vii—Ca1—Ca1viii	135.0
O1i—La1—O1	71.917 (18)	S2viii—Ca1—Ca1viii	45.0
O1ii—La1—O1	112.29 (4)	S2ix—Ca1—Ca1viii	90.0
F1i—La1—O1	71.917 (18)	Ca1ii—Ca1—Ca1viii	180.0
F1ii—La1—O1	112.29 (4)	Ca1vii—Ca1—Ca1viii	90.0
F1—La1—O1	0.0	Ca1v—Ca1—Ca1viii	90.0
O1iii—La1—O1	71.917 (18)	S1—Ca1—Bi1ii	90.0
O1i—La1—F1iii	112.29 (4)	S2—Ca1—Bi1ii	45.0
O1ii—La1—F1iii	71.917 (18)	S2vi—Ca1—Bi1ii	135.0
F1i—La1—F1iii	112.29 (4)	S2vii—Ca1—Bi1ii	45.0
F1ii—La1—F1iii	71.917 (18)	S2viii—Ca1—Bi1ii	135.0
F1—La1—F1iii	71.917 (18)	S2ix—Ca1—Bi1ii	90.0
O1iii—La1—F1iii	0.0	Ca1ii—Ca1—Bi1ii	0.000 (15)
O1—La1—F1iii	71.917 (18)	Ca1vii—Ca1—Bi1ii	90.0
O1i—La1—S1	138.93 (2)	Ca1v—Ca1—Bi1ii	90.0
O1ii—La1—S1	138.93 (3)	Ca1viii—Ca1—Bi1ii	180.0
F1i—La1—S1	138.93 (2)	S1—Ca1—Bi1viii	90.0
F1ii—La1—S1	138.93 (3)	S2—Ca1—Bi1viii	135.0
F1—La1—S1	70.49 (4)	S2vi—Ca1—Bi1viii	45.0
O1iii—La1—S1	70.49 (4)	S2vii—Ca1—Bi1viii	135.0
O1—La1—S1	70.49 (4)	S2viii—Ca1—Bi1viii	45.0
F1iii—La1—S1	70.49 (4)	S2ix—Ca1—Bi1viii	90.0
O1i—La1—S1iv	70.49 (4)	Ca1ii—Ca1—Bi1viii	180.0
O1ii—La1—S1iv	70.49 (4)	Ca1vii—Ca1—Bi1viii	90.0
F1i—La1—S1iv	70.49 (4)	Ca1v—Ca1—Bi1viii	90.0
F1ii—La1—S1iv	70.49 (4)	Ca1viii—Ca1—Bi1viii	0.000 (15)
F1—La1—S1iv	138.93 (3)	Bi1ii—Ca1—Bi1viii	180.0
O1iii—La1—S1iv	138.93 (2)	La1i—F1—La1viii	108.082 (18)
O1—La1—S1iv	138.93 (3)	La1i—F1—La1iii	112.29 (4)
F1iii—La1—S1iv	138.93 (2)	La1viii—F1—La1iii	108.082 (18)
S1—La1—S1iv	135.72 (11)	La1i—F1—La1	108.082 (18)
O1i—La1—S1ii	138.93 (3)	La1viii—F1—La1	112.29 (4)
O1ii—La1—S1ii	70.49 (4)	La1iii—F1—La1	108.082 (18)
F1i—La1—S1ii	138.93 (3)	La1i—O1—La1viii	108.082 (18)
F1ii—La1—S1ii	70.49 (4)	La1i—O1—La1iii	112.29 (4)
F1—La1—S1ii	138.93 (3)	La1viii—O1—La1iii	108.082 (18)
O1iii—La1—S1ii	70.49 (4)	La1i—O1—La1	108.082 (18)
O1—La1—S1ii	138.93 (3)	La1viii—O1—La1	112.29 (4)
F1iii—La1—S1ii	70.49 (4)	La1iii—O1—La1	108.082 (18)
S1—La1—S1ii	81.84 (4)	Ca1—S1—La1	112.14 (5)
S1iv—La1—S1ii	81.84 (4)	Ca1—S1—La1vi	112.14 (5)
O1i—La1—S1v	70.49 (4)	La1—S1—La1vi	135.72 (11)
O1ii—La1—S1v	138.93 (3)	Ca1—S1—La1vii	112.14 (5)
F1i—La1—S1v	70.49 (4)	La1—S1—La1vii	81.84 (4)
F1ii—La1—S1v	138.93 (3)	La1vi—S1—La1vii	81.84 (4)
F1—La1—S1v	70.49 (4)	Ca1—S1—La1viii	112.14 (5)
O1iii—La1—S1v	138.93 (3)	La1—S1—La1viii	81.84 (4)
O1—La1—S1v	70.49 (4)	La1vi—S1—La1viii	81.84 (4)
F1iii—La1—S1v	138.93 (3)	La1vii—S1—La1viii	135.72 (11)
S1—La1—S1v	81.84 (4)	Ca1—S2—Bi1iv	179.8
S1iv—La1—S1v	81.84 (4)	Ca1—S2—Ca1iv	179.82 (17)
S1ii—La1—S1v	135.72 (11)	Bi1iv—S2—Ca1iv	0.0
S1—Ca1—S2	89.91 (9)	Ca1—S2—Ca1v	90.0
S1—Ca1—S2vi	89.91 (9)	Bi1iv—S2—Ca1v	90.0
S2—Ca1—S2vi	179.82 (17)	Ca1iv—S2—Ca1v	90.0
S1—Ca1—S2vii	89.91 (9)	Ca1—S2—Ca1ii	90.0
S2—Ca1—S2vii	90.000 (1)	Bi1iv—S2—Ca1ii	90.0
S2vi—Ca1—S2vii	90.000 (1)	Ca1iv—S2—Ca1ii	90.0
S1—Ca1—S2viii	89.91 (9)	Ca1v—S2—Ca1ii	179.82 (17)
S2—Ca1—S2viii	90.000 (1)	Ca1—S2—Bi1ii	90.0
S2vi—Ca1—S2viii	90.0	Bi1iv—S2—Bi1ii	90.0
S2vii—Ca1—S2viii	179.82 (17)	Ca1iv—S2—Bi1ii	90.0
S1—Ca1—S2ix	180.0	Ca1v—S2—Bi1ii	179.82 (17)
S2—Ca1—S2ix	90.09 (9)	Ca1ii—S2—Bi1ii	0.00 (2)
S2vi—Ca1—S2ix	90.09 (9)	Ca1—S2—Bi1v	90.0
S2vii—Ca1—S2ix	90.09 (9)	Bi1iv—S2—Bi1v	90.0
S2viii—Ca1—S2ix	90.09 (9)	Ca1iv—S2—Bi1v	90.0
S1—Ca1—Ca1ii	90.0	Ca1v—S2—Bi1v	0.00 (2)
S2—Ca1—Ca1ii	45.0	Ca1ii—S2—Bi1v	179.82 (17)
S2vi—Ca1—Ca1ii	135.0	Bi1ii—S2—Bi1v	179.82 (17)
S2vii—Ca1—Ca1ii	45.0	Ca1—S2—Ca1ix	89.91 (9)
S2viii—Ca1—Ca1ii	135.0	Bi1iv—S2—Ca1ix	89.9
S2ix—Ca1—Ca1ii	90.0	Ca1iv—S2—Ca1ix	89.91 (9)
S1—Ca1—Ca1vii	90.0	Ca1v—S2—Ca1ix	89.91 (9)
S2—Ca1—Ca1vii	135.0	Ca1ii—S2—Ca1ix	89.91 (9)
S2vi—Ca1—Ca1vii	45.0	Bi1ii—S2—Ca1ix	89.9
S2vii—Ca1—Ca1vii	45.0	Bi1v—S2—Ca1ix	89.9