Silicate composites ionic conductivity

The silicate-phosphate series of composition Nai+ Zr2(P04)3 (Si04) can be obtained by heating together sodium carbonate, ammonium dihydrogen phosphate, zirconia and silica. When x lies in the range 1.8-2.2, the solid ( Nasicon ) has exceptionally good ionic conduction properties, arising from the mobility of Na+ within the occupied and unoccupied cation sites in the three-dimensional channel structure. 

Like their silicate analogues the sodium rare earth germanates of composition Na5RGc40i2 show high ionic conductivity. The alkali cations can move freely in the structure. The conductivity values observed in the germanates lie between 10 and 12 cm (Shannon et al., 1978 Hong et al., 1978). 

The further study on sol-gel preparation of MEEP-silicate composite materials involved the synthesis of a polyphosphazene precursor via the covalent linkage of MEEP with an organometallic alkoxide (triethoxysilane group) [63]. The following hydrolysis and condensation produced a covalently interconnected hybrid material with controlled morphologies and physical properties. A maximum ionic conductivity of 7.69 X10 S cm was achieved for the composite materials complexed with LiTFSI salt. 

This situation, clear in the case of more ionic structures, is less stringent in graphite intercalates where, presumably, there is electron transfer to (in the case of alkali-metal intercalates) or from (in the case of metal halide intercalates) the half-filled conduction bands of the graphite layers (produced by overlap of the 7t orbitals). Similarly, the periodicity requirements are less stringent for the alternating composite layers of layer silicates with complex intralayer and interlayer charge balance. 

The properties of slags are dependent not only upon chemical composition, but upon other factors also. The most pronounced deviations from additivity rules based on composition arise in the estimation of those properties which involve ionic transport eg. electrical conductivity. However surface tension values estimated from additivity rules are frequently in error as bulk thermodynamic properties do not apply at surfaces. Furthermore, virtually all the physical properties of slags are, to some extent, dependent upon the structure of the slag (viz. the length of silicate chains, degree of crystallinity etc.) thus estimation procedures have to accommodate these structural factors, where possible. 

The hosts that we have discussed to date have been ionic in nature, and dielectric as well (they are non-conductive). There is also another class of phosphor hosts which are covalent and semi-conductive in nature, namely the zinc and cadmium sulfides and/or selenides. The criterion for selection of a semi-conducting host for use as a phosphor includes choice of a composition with an energy band gap of at least 3.00 ev. This mandates the use of an optically inactive cation, combined with sulfide, selenide and possibly telluride. The ojq gen-dominated groupings such as phosphate, or silicate or arsenate, etc. are not semi-conductive in nature. And, none of the other transition metal sulfides have band gaps sufficiently... 

According to recent developments in the field, the term molten salts can advantageously be widened in scope to encompass many molten media which may not be wholly ionic or derived from simple salts. Thus, many systems studied within this broad classification may change their ionicity and hence conductivity according to temperature, pressure, or composition, e.g., silicates, group IIB chlorides, and chloroaluminates, respectively. Nevertheless, the majority of melts that have been studied are substantially dissociated in the liquid state, and all processes conducted in these are ipso facto electrochemical. Many of the processes considered here, therefore, involve charge transfer systems, particularly between solids (mainly metals) and melts, viz., electrode processes. ... 

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