Lanthanum trifluoride

Solubility Products for Lanthanum Trifluoride and Cerium Trifluoride in Aqueous Solution at 25°C ... 

Cerium trifluoride is known to be insoluble in liquid ammonia (278). Lanthanum trifluoride is very sparingly soluble in bromine trifluoride ... 

It is incorrect to vacuum-plate the internal side of the membrane with silver or gold in the fluoride ISE containing the lanthanum trifluoride membrane [177]. 

The group of ion-selective electrodes with fixed ion-exchange sites includes systems with various membrane structures. The membranes are either homogeneous (single crystals, pressed pellets, sintered materials) or heterogeneous, set in an inactive skeleton of various polymeric materials. Important electrode materials include silver halides, silver and divalent metal chalcogenides, lanthanum trifluoride and various glassy materials. Here, the latter will be surveyed only briefly, for the sake of completeness. 

The determination of fluoride ions has always been difficult, so the discovery of the lanthanum trifluoride electrode by Frant and Ross in 1966 was a great step forward. Until recently, this was the most important sensor in the ISE field, except for the glass electrode sensitive to hydrogen ions. The extraordinary specificity of this electrode made the greatest contribution to its usefulness. The only important interferent is the hydroxide ion. 

The fluoride electrode is a typical example of an ion selective electrode. Its sensitive element is a crystal of lanthanum trifluoride that allows fluorine atoms to migrate into the network formed by lanthanum atoms (Fig. 18.3). Other electrodes use a mineral membrane obtained as agglomerates of crystalline powders (for measurement of Cl-, Br-, I , Pb++, Ag+ and CN ). Generally, the internal electrolyte can be eliminated (by dry contact). However, it is preferable to insert a polymer layer with a mixed-type conductivity to ensure the passage of electrons from the ionic conductivity membrane to the electronic conductivity electrode (Fig. 18.3). 

Despite all the technological applications and investigations of rare-earth YAG lasers, the optical spectra of some of the rare-earth ions in this host are of questionable quality and in some cases nonexistent. Only two rare-earth ions in YAG, neodymium and erbium, have been thoroughly investigated and reported. This is rather surprising when compared to lanthanum trifluoride (LaFa), for which Kaminskii reports only 16 lasers, although abundant excellent data exist (Camall et al., 1977) for all of the rare-earth ions in LaFs except terbium. 

FIGURE 1 Potential energy function of the out-of-plane bending vibration and vibrational energy levels (horizontal lines) calculated by Gorokhov and Osina (2002) and in the harmonic approximation (on the right) for lanthanum trifluoride p is the angle between the La-F bond and the normal to the threefold symmetry axis. 

The silver(i)-catalysed oxidation of americium(iii) by SgOg " has been studied using Am tracer techniques, coprecipitation with lanthanum trifluoride representing a good method of monitoring the micromolar... 

Fig. 20. Nine-fold coordination of lanthanum in lanthanum trifluoride as viewed down the c-axis (Zalkin et al. 1966). (Reprinted by permission of the publisher, The American Chemical Society.)...

A. Zalkin, D. H. Templeton, Refinement of the trigonal crystal stmcture of lanthanum trifluoride with neutron diffraction data, Acta Crystallogr., B 41, 91-93 (1985). 

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