A poor semiconductor

The conductivity changes in a discontinuous fashion at a composition of approximately x = 0.12 at which composition the metal becomes a poor semiconductor. The formula is now Li [LiJi2Ti044Tut4]O4. This transition is reversible. Donor doping of insulating Li4/3Ti5/304 will return the compound to the metallic state. 

Ten years later, the polyacetylene story moved from Italian academe to American industry, when two chemists working for Cyanamid, Berets, and Smith took Natta s dark powder and compressed it into a disc that turned out to be a poor semiconductor, the conductivity of which increased in the presence of volatile oxidants like iodine and decreased in the presence of ammonia vapor. 

Preliminary measurements of electrical conductivity of the conjugated derivatives of PBTAB, PBTB and PTTB obtained by the above treatment with bromine vapor are poor semiconductors with a conductivity of the order 10 °S/cm which apparently is not due to doping. Subsequent electrochemical or chemical doping of these polymers lead to 4-6 orders of magnitude increase in conductivity. Ongoing studies of the electrical properties of these conjugated polymers with alternating aromatic/quinonoid units will be reported elsewhere. 

The arrangement of zinc and sulfur atoms in the Zn4S core is similar to the observed Zn40. Theoretical calculations demonstrated that the compound is a poor model of extended metal chalcogenide semiconductors (ZnS). Octanuclear zinc compounds have also been structurally characterized with this core. In the presence of an alkylammonium cation, a sulfide containing octanuclear zinc species was formed [BzEt3N]2[Zng(S)(SBz)i6].126 The complexes with benzylthiolate... 

Grain boundary defects are primarily responsible for the operation of zinc oxide (ZnO) varistors, a shortened form of variable resistor. The varistor behaves like an insulator or poor semiconductor at lower electrical field strengths, but at a critical breakdown voltage the resistance decreases enormously and the material behaves like an electrical conductor (Fig. 3.36). When a varistor is connected in parallel with electrical equipment, negligible power flows through it under normal low... 

The compound will be stoichiometric, with an exact composition of MX10ooo when the number of metal vacancies is equal to the number of nonmetal vacancies. At the same time, the number of electrons and holes will be equal. In an inorganic compound, which is an insulator or poor semiconductor with a fairly large band-gap, the number of point defects is greater than the number of intrinsic electrons or holes. To illustrate the procedure, suppose that the values for the equilibrium constants describing Schottky disorder, Ks, and intrinsic electron and hole numbers, Kc, are... 

There are several possible reasons why the overall rate of electron transfer is slow. Occasionally, it is because the electrode is a poor conductor, such as semiconductors like silicon or poor metals such as tungsten (see SAQ 2.6). Fabricating an electrode from metals such as platinum, gold, or from metallic conductors such as graphite or glassy carbon, will circumvent that possibility. 

Like other non-oxidic semiconductors in aqueous solutions, surface oxidized and photocorrosive InP is a poor photoelectrode for water decomposition [19,27,32,33], To enhance properties several efforts have focused on coupling of the semiconductor with discontinuous noble metal layers of island-like topology. For example, rhodium, ruthenium and platinum thin films, less than 10 nm in thickness, have been electrodeposited onto p-type InP followed by a brief etching treatment to achieve an island-like topology on the surface [27,28]. In combination with a Pt counter electrode, under AM 1.5 illumination of 87 mW/cm the metal (Pt, Rh, Ru) functionalized p-InP photocathodes [27] see a reduction in the threshold voltage for water electrolysis from 1.23 V to 0.64 V, and in aqueous HCl solution a photocurrent density of 24 mA/cm with a photoconversion efficiency of 12% [27]. 

Since the publication of the original observation in 1977 there has been an explosive growth of research into the whole range of conjugated polymer structures which has led to the development of a new family of polymers which, with appropriate chemical modification, can display conductivities from poor semiconductor to comparable with copper. These polymers have obviously been the result of major contributions from synthetic chemists and have been of great interest to solid-state physicists. Somewhat surprisingly there has been less interest on the part of polymer scientists. This has led to problems in many areas, partly because of failure to recognise the... 

LaFe4Sbn is a poor metal or heavily doped semiconductor with good thermoelectric properties above room temperature (700-1000 K) (Sales et al., 1996, 1997). Only polycrystalline samples have been investigated. The room temperature resistivity is about 0.5 m 2cm de-... 

Electrical conductivity measurements have been made on a few of these metal dithiolene systems and show that they are, at best, poor semiconductors, with room-temperature conductivities of less than 10 6Q 1cm 1. This is not surprising as the molecules are in an integral oxidation state. Moreover, the existence of dimers destroys the crystallographic uniformity of the stacks and, as the magnetic studies have shown, the unpaired electrons tend to couple within the dimers rather than delocalize along the stacks. 

On Figure 8 the hole concentration is plotted against vacancy concentration. A theoretical curve calculated on the basis of two carriers per vacancy is also shown. There is a very poor agreement between the two curves. To get the theoretical curve to fit the experimental points, it is necessary to assume more than two carriers per vacancy. This is difficult to reconcile. It is apparent that SnTe is not a simple semiconductor like GeTe. At present single crystals of SnTe are being investigated at our laboratory, at the U. S. Naval Ordnance Laboratory, and at Lincoln Laboratory. Preliminary results indicate a complex band structure for this compound (1,2,5). 

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