Concurrent Pathways in the Phase Transitions of Alloys and Oxides: Towards an Unified Vision of Inorganic Solids - Inorganic 3D Structures - page 156

a b

BaCl 2 Fe 2 P

c d

Ba 2 Cl 3 BaCl 3

e

f

Ba 3 Cl 3 NiIn, FeGe, CoSn

Fig. 14 (a) The hexagonal ( 62m) structure of BaCl 2 projected on the ab plane. Grey and green

spheres represent Ba and Cl atoms, respectively. (b) The aristotype Fe 2 P structure showing the
graphite-like layers formed by the P atoms ( purple spheres ) and the two types of tricapped trigonal
prisms (TCTPs) formed by the Fe atoms ( green and light brown spheres ). (c) The structure of
BaCl 2 in which the columns of TCTP centred at the cell origin have been omitted. The result is a
frame of stoichiometry Ba 2 Cl 3 .(d) The subarray formed by Ba(1) and Cl(2) forming the columns
omitted in (c). They form the columns of TCTP of composition BaCl 3 which are related to the
LaCl 3 structure. (e) The same structure projected in (c) but adding the Ba(1) atoms, located at the
origin, producing so a stoichiometry Ba 3 Cl 3 which is a distortion of the NiIn, CoSn and FeGe
structures represented in (f)

P

obtained in two independent ways [ 31 , 56 ] . The unit cell dimensions are a ¼ 8.10,

4.65 ˚ , Z

c 3, with atoms occupying four crystallographically independent

sites, i.e. Cl(1) at 3 g , Cl(2) at 3 f , Ba(1) at 2 d (1/3, 2/3, 1/2) and Ba(2) at 1 a (0, 0, 0).
In Fig. 14a, b are represented the structures of BaCl 2 and Fe 2 P, respectively, and the
Co 2 Si-type structure of BaCl 2 is shown in Fig. 18c .

¼ ¼