Tysonite structure

Lanthanide and actinide trifluorides adopt a different structure called the tysonite structure (DOg). In this structure, the metal atom has the unusual eleven (5 -I- 6) coordination. Covalent AB3 halides crystallize in layer structure (DO5) typified by CrCl3 and Bil3 these structures are related respectively to CdCl2 and Cdl2. 

Much of the structural data are based on powder X-ray diffraction, but structures are typically polymeric with the bismuth in a distorted nine-coordinate environment similar to that in BiF3 or the Tysonite structure. There has been considerable interest in these compounds as fast fluoride ion conductors. ... 

Colorless solid, insoluble in water. Hexagonal (tysonite) structure. 

Rare-earth fluorides exist either as hexagonal (Lap3) or as orthorhombic structures ((3-YP3), as shown in fig. 17 for rare-earth fluorides with La to Lu (Thomas and Brunton 1966). Pluorides of the rare-earth elements La to Nd crystallize in the tysonite structure at all temperature ranges below the melting point. Smp3 to Gdp3 are orthorhombic at lower... 

It was shown for Bii xBax(0,F)3 s oxyfluorides with tysonite structure that introducing oxygen ions into modification 1 of this phase leads to the conductivity decrease and into modification II to its increase (Figure 14.5) [11]. 

Tysonite Structure, Tysonite Modifications and Anion Defects... 

The name of the tysonite structural type comes from the mineral tysonite, a solid solution of cerium and other RE fluorides in LaF3. There are two modifications of the tysonite... 

Figure 14.27 Projection of the hexagonal (a) and trigonal (b) tysonite structures onto the xOy...

The following phases have the hexagonal tysonite structure I the mineral tysonite, ThOF2 [86] and BiOo.iFi.s [87] oxyfluorides and M Ri-xPs-x solid solutions (R = Gd-Er M = Ca, Sr) [88]. Possibly, the high anion defects concentration (Op and Vp) promotes stabilization of this modification. The limits of x in the M Ri-xPs-x solid solutions are 0.07[Pg.451]

The following phases adopt the trigonal tysonite structure II La-Nd trifluorides, solid solutions on their basis MxRi xP3-2x (M = Ca, Sr, R = La-Nd) [88] and BaxBii xFa x [44]. 

The tysonite structure is close to the structure of orthorhombic 0-YFj [91] (Figure 14.30). Orthorhombic Bip3 crystallizes also in (d-YF stmctural type [91]. Bip3 transfers under slight static pressure (15 3kbar) to tysonite type structure [8]. 

Rare-earth trifluorides crystallize in three structural types the tysonite structure type, the hexagonal Or-YF3 structural type and orthorhombic P-YF structural type [7]. 

Figure 14.34 F - ions migration paths in LaF. (Reprinted with foermission from [111]. View of the tysonite structure perpendicular to the c-axis ( c) the different sites are ordered in different layers (sequence AAB along the c-axis A contains only FI, B only F2/F3 sites).

Conductivity mechanism in phases with the tysonite structure (LaFj as an... 

The influence of different doping types on the defect structure and conductivity of fluorine-containing phases with fluorite and tysonite structures has been discussed in the current review. The defect-region model including clustering and percolation phenomena has been used for describing the ionic transfer features in soUd solutions. 

M. Izosimova, A. I. Livshits, V. M. Buznik, P. P. Fedorov, E. A. Krivandina, B. P. Sobolev, Diffusion mechanism of F-ions in solid electrolytes with tysonite structure, Fiz. Tverd. Tela (S.-Petersburg), 28, 2644-2647 (1986) (in Russian). 

A. F. Privalov, H-M. Vieth, I. V. Murin, Nuclear magnetic resonance study of superionic conductors with tysonite structure, J. Phys. Condens. Matter, 6, 8237-8243 (1994). 

---