A new ternary antimonide phase, LiBaSb

Lithium barium antimony, LiBaSb, crystallizes in the centrosymmetric hexagonal space group P6₃/mmc. Ba atoms sit on positions with m symmetry, while the Sb and Li atoms occupy sites of 2m symmetry. The structure of LiBaSb contains alternate hexagonal layers of (LiSb) and Ba. In this compound, antimony is present as isolated Sb^3- species. The Ba atom lies inside a hexagonal prism (6 × Li and 6 × Sb).

Key indicators

• Single-crystal X-ray study
• T = 293 K
• R factor = 0.022
• wR factor = 0.055
• Data-to-parameter ratio = 16.0

checkCIF results

No syntax errors found



ADDSYM reports no extra symmetry


 Alert Level A:



GEOM_005  Alert A _geom_angle_atom_site_label_1 is missing
          Label identifying the atom site 1.

GEOM_006  Alert A _geom_angle_atom_site_label_2 is missing
          Label identifying the atom site 2.

GEOM_007  Alert A _geom_angle_atom_site_label_3 is missing
          Label identifying the atom site 3.

GEOM_008  Alert A _geom_angle is missing
          Angle between atom sites 1, 2 and 3.


 Alert Level C:



ABSTY_02  Alert C An _exptl_absorpt_correction_type has been given without
          a literature citation. This should be contained in the
          _exptl_absorpt_process_details field.
          Absorption correction given as numerical

CRYSR_01  Alert C _exptl_crystal_size_rad not in the CIF when expected.

General Notes



ABSTM_02  The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.439     0.541
          Tmin and Tmax expected:      0.310     0.458
          RR =      1.200
          Please check that your absorption correction is appropriate.


 4 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 2 Alert Level C = Please check

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S1. Comment

The structure of LiBaSb has been determined in the centrosymmetric space group P6₃/mmc (No. 194). Ba and Sb atoms were refined anisotropically, and an attempt to refine the Li atom anisotropically resulted in an uncertainties/U^ij ratio that was too large. This compound is isostructural with KZnSb (Savelsberg & Schaefer, 1986) and NaBeSb (Tiburtius & Schuster, 1977), but the atomic positions of the monovalent and divalent cations are exchanged. In the LiBaSb structure, Li occupies the 6m2 site and Ba the 3 m site, while in KZnSb (or NaBeSb), K (or Na) sits at 3 m and Zn (or Be) at 6m2. The ionic radius of Li⁺ (0.90 Å) is closer to that of Zn²⁺ (0.88 Å) (or Be²⁺ 0.60 Å) than to that of K⁺ (1.52 Å) [or Na⁺ (1.20 Å)]. This favors exchange of monovalent/divalent atom positions. This structure can be considered as a filled NiAs-type structure or is better described as a substituted Li₃Sb structure; one Ba²⁺ substitutes two Li⁺ cations. The LiBaSb structure adopts the same space group as Li₃Sb. Owing to the largest size of the barium cations (Ba²⁺ 1.49 Å) compared with Li⁺ (0.9 Å), the cell parameters of the ternary phase are expanded (a = 4.701 Å and c = 8.309 Å in Li₃Sb). Atomic positions are different from those in the binary phase. The structure of LiBaSb may be described with hexagonal prisms Ba(Li₃Sb₃)₂ fused along the c axis. The barium cations are surrounded by 6 Li and 6 Sb atoms at 3.616 (1) Å. The Sb atoms are coordinated to three Li cations at 2.828 Å, close to the Li—Sb distance in Li₃Sb (2.71 and 2.77 Å), and to six Ba cations at 3.616 (1) Å.

Unlike the parent Li₄Ba₃As₄ compound (Monconduit & Belin, 1999), which contains two anionic moieties, namely As₂^4- dumbbells and isolated As^3- anions, and was characterized as a large band semi-conductor, the LiBaSb (Li⁺Ba²⁺Sb^3-) compound contains only isolated Sb^3- anions in association with Li⁺ and Ba²⁺ cations and is an insulator.

S2. Experimental

In the aim of obtaining the ternary compound Li₄Ba₃Sb₄, amounts of Li, Ba and Sb (in proportion 4/3/4) were inserted in a niobium reactor, then weld-sealed under argon·The niobium reactor was protected against oxidation inside an evacuated silica tube. Single crystals of LiBaSb were obtained as side products by heating the initial mixture at 780 K for 10 h, maintaining at 580 K for 3 days and quenching in air. Elemental analyses (SEM) of crystals confirmed the presence of barium and antimony nearly in the ratio 1:1. The air-sensitive crystals were inserted into Lindemann glass capillaries for X-ray data investigations. Parameters and crystallographic space group were initially determined by oscillation and Weissenberg techniques. The best diffracting crystal was used for accurate intensity measurements on a CAD-4 Nonius diffractometer. Space group was found to be P6₃/mmc (n° 194) (observation conditions: 00 (0) l for l = 2n and hh(-2 h)l for l=2n).

S3. Refinement

All computations were carried out on a Pentium II 266 computer. The structure representation has been drawn with the program ORTEP-3 for Windows (Farrugia, 1997) which is a MS-Windows version of the current release of ORTEP-III (Burnett & Johnson).

Computing details

Figures

Fig. 1. Representation of the hexagonal unit cell of LiBaSb. Barium cations are shown inside the hexagonal Li6Sb6 prism. Li atoms are represented by blue circles, Ba atoms by green circles and Sb atoms by red circles. Displacement ellipsoids are drawn at the 90% probability level.

(LiBaSb)

Crystal data

?	β = ?°
Mr = ?	γ = ?°
?, ?	V = ? Å^3
a = ? Å	Z = ?
b = ? Å	? radiation, λ = ? Å
c = ? Å	× × mm
α = ?°

Data collection

h = ?→?	l = ?→?
k = ?→?

Refinement