Halide Fluorites

The ionic conductivity of fluorite-structured halides such as SrF2, CaF, BaF, (3- Pb F 2, and SrCh, shows a rapid but continuous increase on heating, reaching values very dose to those shown by the liquid state [67-69]. The transition to the superionic state is also associated with peak in the specific heat Cp (the maximum value of which is generally taken to define the superionic transition temperature, f), anomalous behavior ofthe elastic constants and changes in the lattice expansivity (for details and references, see Refs. [38, 70]). 

At temperatures well below f. the defect concentration is very low and dominated 

Of all the fluorite-structured halides, P-PbF2 has attracted the most attention, since it has the lowest superionic transition temperature (Tc = 711 K). The ionic conductivity and structural properties of a number of compounds based on PbF2 have been studied, with the ternary compound PbSnF4 possessing one of the highest values of ionic conductivity of any F ion conductor at ambient temperature ( 7, = 10 S cm- [76]). 

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Halide Fluorite (fluorospar) CaF2 All colors 3.18 1.433 4 Perfect cleavage in four directions... 

Halides Fluorite CaFg Lasers and electronics (pure... 

Goldschmidt predicted from his empirical rule that calcium chloride would not have the fluorite structure, and he states that on investigation he has actually found it not to crystallize in the cubic system. Our theoretical deduction of the transition radius ratio allows us to predict that of the halides of magnesium, calcium, strontium and barium only calcium fluoride, strontium fluoride and chloride, and barium fluoride, chloride,... 

Halides Metal ion(s) + halogen ion Common salt (sodium chloride), a component of animal diets Fluorite (calcium fluoride), a lapidary material and flux... 

In the arsenide and antimonide derivatives Na2AuAs or Na2AuSb there are zigzag (AuX)2 -chains, with structures like the gold(I) halides (4), while AuSb2 has metallic properties and has the cubic fluorite structure.325-327... 

Ilia Simple halides halite NaCl, fluorite CaF2, chlorargyrite AgCl... 

Our work has applied these techniques to the study of the binary insulating materials including the fluorites, alkali halides, alkaline earth oxides, and perovskites. Many of these are simple materials that are commonly used as models for all solid state defect equilibria. Our work has had the goal of determining at the microscopic level the defect equilibria and dynamics that are important in understanding solid state chemistry as well as developing new tools for the studies of solid materials. 

Electronic Excitation. The storage of energy in an insulating material by the absorption of ionizing radiation occurs via two major processes, namely, electronic excitation and displacement damage. Radiation damage by these processes in insulators has been a topic of intense research for decades and several excellent review articles already exist concerning a variety of material types (eg. oxides (1-5), alkali halides (6-8) and fluorites (9)). 

The triboluminescence of minerals has been studied visually (see the footnotes to Table I) but only a few minerals have been examined spectroscopically. There are a few clear examples of noncentric crystals, such as quartz, whose emission is lightning, sometimes with black body radiation. Most of the triboluminescent minerals appear to have activity and color which is dependent on impurities, as is the case for kunzite, fluorite, sphalerite and probably the alkali halides. Table I attempts to distinguish between fracto-luminescence and deformation luminescence, but the distinctions are not clear cut. A detailed analysis of the structural features of triboluminescent and nontriboluminescent minerals may make it possible to draw conclusions about the nature and concentration of trace impurities that are not obvious from the color or geological site of the crystals. Triboluminescence could be used as an additional method for characterizing minerals in the field, using only the standard rock hammer, with the sensitive human eye as a detector. 

Many inorganic compounds have the fluorite and inverse fluorite structures (a) all halides of the larger divalent cations except two fluorides in this class (b) oxides and sulfides of univalent ions (c) oxides of large quadrivalent cations and (d) some intermetallic compounds. Table 10.1.5 lists some compounds of the fluorite and inverse fluorite types and their a parameters. 

Halides are compounds that include one of the halogen elements fluorine, chlorine, bromine, or iodine. The simplest halides are combinations of one element, such as sodium (Na), with a halogen element, such as chlorine (Cl). Complex halides combine two or more elements with a halogen, and some contain water. Some halides are economically important minerals, such as halite (common salt), fluorite (fluorine), and chlorargyrite (silver ore). 

All four halides, HgX2, are known their structures are summarized in Table 15-6 and some properties are given in Table 15-7. Mercury(II) fluoride has the fluorite structure and is not volatile. It is decomposed by water, as might be expected since HgO and HF are both weakly dissociated. No fluoro complex of Hg2+ is known. 

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