Tysonite-type structure

The compounds with fluorite- and tysonite-type structures meet all these requirements very well (Table 14.1). The high ionic conductivity of these compounds combines with relative low electronic conductivity (usually no more than 0.1 % of the total conductivity [1]). This is a significant reason for their application as solid electrolytes. 

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]. 

N. I. Sorokin, B. P. Sobolev, (Conductivity of single crystal solid solutions Lai xSrxp3 x (0 < X < 0.15) with tysonite-type structure, Kristallografiya, 39, 889-893 (1994) (in Russian). 

The trifluorides of lanthanum and ceriiun through samarium adopt the tysonite type of structure with elevenfold coordination of the metal ion (Wells 1975). The [RFn] unit. 

Schubert (1989) points out that radius ratio considerations in LaFj would suggest coordination near LaFg, and the LaFj structure should therefore be homeotypic with CaFj. He then relates the LaFj structure to that of CaFj, compares the displacements to those of related structures, e.g., CaFj-YFj superstructures, and discusses crystal energetics. LaFj crystals were examined by DSC from 100 -500 K an anomaly which occurs in the Cp versus T curve is related to a phase transition in which the fluoride sublattice fuses (Aliev and Fershtat 1984). This phenomenon appears related to the high ionic conductivity of the tysonite-type fluoride phases. 

That is why in the current chapter we will confine ourselves to the ionic transfer discussion of fluorine-conductive fluorites and tysonites from a slightly different standpoint we wiU try to observe an influence of various doping types on the structure features and the defect structure of nonstoichiometric fluorine-containing phases. 

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... 

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]. 

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. 

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