NaTl type

NaTl type, diamond-like Hg partial structures [4]... 

The cF16-NaTl type structure is face centred, cubic, space group Fd3m, N. 227. Atomic positions ... 

The NaTl-type structure may be conveniently compared with the Li3Bi and MnCu2Al types all these structures which have cF16-unit cells may be considered as... 

For the layer stacking symbols, the data are reported in comparison with the Li3Bi and NaTl-type structures Strukturbericht designation L2,. 

Layer stacking symbols of the NaTl type and of the NaTl-related types are here reported ... 

The NaTl-type structure is the prototype for Zintl phases, which are inter-metallic compounds which crystallize in typical non-metal crystal structures. Binary AB compounds LiAl, LiGa, Liln and Naln are both isoelectronic (isovalent) and isostructural with NaTl. In the Li2AlSi ternary compound, A1 and Si form a diamond-like framework, in which the octahedral vacant sites of the A1 sublattice are filled by Li atoms, as shown in Fig. 13.7.2(b). 

From the crystal structure, physical measurements, and theoretical calculations, the nature of the chemical bond in the NaTl-type compound AB can be understood in the following terms ... 

The electronic properties of binary and ternary intermetallic Zintl phases crystallizing in the NaTl type of structure are investigated and reported. The crystal and defect structure, the electronic band structure and density of states, the bonding mechanisms and the charge transfer are discussed. Comparison is made between the electronic states in the B2 and the B32 types of structure. Furthermore, based upon theoretical studies of the electronic valence states the optical properties (imaginary part of the dielectric constant and reflectivity) and the magnetic properties (susceptibility and Knight shift) are considered. 

The present work will only consider the electronic properties of those Zintl phases which crystallize in the B32 structure. Binary B32 Zintl phases are formed by the AB compounds LiAl, LiGa, Liln and Naln, by the prototype NaTl, and by the AB compounds LiZn and LiCd. Ternary systems, which crystallize in this structure, are found for alloys ABi-,Cx, for which at least one boundary compound AB or AC crystallizes in the NaTl type of structure. 

The number of AB compounds which crystallize in the B2 type of structure is much larger than those which form B32 type Zintl phases. As pointed out in Section B the NaTl type is restricted to alloys for which the sizes of the parent atoms are almost equal... 

Colored Zintl phases, which crystallize in the NaTl type of structure, are found for the alloys Li2Cd2-xInx, 0.6 < x < 1.0 and Li2Zn2-,Cd 1.2 < x < 1.6. The optical constants (reflectivity r, polarization Ci and absorption E2) were determined for these sys-... 

Theoretical values for 2, max calculated for the system Li2Cd2-xInx in a simple way from the joint density show the same trend as the experimental finding. Furthermore, the theoretical studies suggest that the optical constants of these phases depend on the specific shape of the electronic bands in the NaTl type of structure. 

LiAl has been shown to possess a crystal structure of the NaTl type. The crystal structure of RaAL shows that it is actually 6a7Ali3, and belongs to the trigonal space group P3ml. The atomic arrangement is very similar to that in the Laves phase prototype, MgNi2-... 

In /8-LiAl (B32 (cF16), NaTl-type structure), vacancies on the Li sublattice are the dominant defect for Ll-deficient compositions (48 to 50 at.V ). Neutron diffraction measurements show that these vacancies order on every tenth (840) plane below 97 K. This vacancy ordering is responsible for anomalies observed in several physical properties around 100 K (electrical resistivity, speciflc heat, nuclear spin-lattice relaxation) (Brun et al., 1983). 

Phase width and valence electron concentration of the ternary cubic Zintl phases of the NaTl type (in German), H. Pauly, A. Weiss, and H. Witte, Zeitschrift fur Metallkunde, 1968, 59(7), 554. 

---