Mixed valence semiconducting

In the case of a mixed-valence salt containing neutral TCNQ there are more TCNQ molecules than there are unpaired electrons and, therefore, electrostatic repulsion of charge carriers Is kept at a minimum by allowing conduction electrons to occupy the empty molecular orbitals of TCNQ . This Is a lower energy pathway compared to putting more than one electron on the seime TCNQ site and It may explain how mixed-valence semiconducting salts like CS2 (TCNQ )s and the "switched" form of Cu-TCNQ can exhibit greater conductivity than similar salts with 1 1 stoichiometry. 

C. U. Pittman, Jr., B. Surynarayanan, Y. Sasaki, Mixed Valence, Semiconducting Ferrocene-Containing Polymers, in Advances in Chemistry Series, Number 150 Inorganic Compounds with Unusual Properties, R. B. King, Ed., pp. 46-55, ACS Publishers, Washington DC, 1976. 

Mixed Valence, Semiconducting Ferrocene-Containing Polymers... 

Some insulating oxides become semiconducting by doping. This can be achieved either by inserting certain heteroatoms into the crystal lattice of the oxide, or more simply by its partial sub-stoichiometric reduction or oxidation, accompanied with a corresponding removal or addition of some oxygen anions from/into the crystal lattice. (Many metal oxides are, naturally, produced in these mixed-valence forms by common preparative techniques.) For instance, an oxide with partly reduced metal cations behaves as a n-doped semiconductor a typical example is Ti02. 

The eight-coordinate vanadium complex V(S2CMe)4 contains both dodecahedral and square prismatic eight-coordinate molecules in the same crystal.322 Of particular interest is the chain-like, mixed valence platinum complex [Pt2(S2CMe)4( i-I)]A, which displays unusual electrical properties metallic conduction between 300 and 340 K and semiconducting properties below 300 K,323 whereas the analogous nickel complex, [Ni2(S2CMe)4(p-I)]x is a semiconductor.324... 

It Is postulated that mixed-valence species or complex salts (12) formed as a result of this field Induced redox reaction control the semiconducting behavior of these films and these complex salts exist In a solid-state equilibrium with the simple 1 1 salt. Since non-integral oxidation states are common In solids, It Is difficult to predict exact stoichiometry In the equilibrium equation, but a likely equation for switching In Cu-TCNQ, for example, may Involve... 

Since the discovery in 1951 that magnetoplumbite, BaFei20i9 is a hard, semiconducting ferrigmagnet of considerable technical interest, several other iron oxides with closely related hexagonal structures have been synthesized and studied. Of particular interest for this review are those containing mixed valency. 

The squarate ion is also assmned to have the potential for providing a pathway for electron conduction when it bridges metal atoms in polymeric complexes (61). Some workers have used partial oxidation to enhance the possibility that compounds will exhibit conductivity. For example, Toftlund (110) showed that the partially oxidized platinum salt K2[Pt(C404)2l 2H2O has the properties of a one-dimensional conductor, while Wrobleski and Brown (18) reported that some mixed-valence iron squarate complexes display semiconductivity. 

Electronic Conductivity. Pluorides usually are good insulators owing to the wide band gap of more than 6eV in most compounds. In some cases it is possible, however, to obtain n-type semiconducting properties by doping, for example, in Cdp2(Y). Exceptional metallic conductivity is observed in the metal-rich compound Ag2p, even superconductivity in Hg3 jAsp6 - despite the presence of fluoride. Mixed-valence silver fluorides have been recently discussed as possible candidates for superconductivity. ... 

A single phase requires specific conditions to be highly active and selective. It has to possess a thermodynamically possible redox with regard to the reactants. It must be a mixed valence phase at the steady state. It must possess a particular morphology exhibiting statistically the selective lattice planes at the surface and must have optimal semiconductivity by "small polarons". 

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