Under-doping

The addition of arylsulfenyl chlorides under doping conditions has also been investigated127 with other compounds of this series where structural features did not permit lactone ring closure and therefore allowed other skeletal transformations. 

Wagner-Meerwein rearrangements occur also when arylsulfenyl chlorides or the mixtures R2NCI + SO3 (R = piperidino, morpholino) add to norbomadiene 393196,197. An addition of 2-nitro- (NBSC) or 2,4-dinitrobenzenesulfenyl chloride to the polyenes 395-397 in AcOH and under doping conditions (AcOH, with LiClO/f) is accompanied by Wagner-Meerwein rearrangements (equations 145-147)198. Thus, new types of struc-... 

The change in solvent polarity thus leads to an appreciable variation in product composition, which is further changed under doping conditions. In the presence of LiClO4 the products indeed arise exclusively from skeletal rearrangements and incorporation of external nucleophiles, solvent and perchlorate anion. The formation of C1O4 -incorporated products can be increased by carrying out the reaction in non-nucleophilic solvents -. ... 

Figure 9a Theoretical predictions of 7. Peaks 1, 2, 3 relate to the under-doped regime (compare with Figure 9b) while peak 4 relates to the over-doped regime (compare with Figure 9c). The broken lines are the expected effect of fluctuations not included in our model.

Figure 9b Experimental data from the Cambridge group (Cooper, Loram et al [29]) for YBCO(Ca 20%) for heat capacity in the under-doped regime...

Fig. 4. Ibimeling spectra of the basal plane of under-doped B12212 with Tc = i3K at various temperatures.

Many selenophene-containing copolymers are available. Most of them were developed as conductive materials, but recent polymers are finding other applications such as light-emitting and photovoltaic materials. Copolymer 14 [57, 58], which consists of selenophene and thiophene, was developed by electropolymerization of 2-thienylselenophene. The conductivity of 14 under doping was of the order of 10 -10 Scm and is almost the same as that of polyselenophene. 

Other features are consistent with non-phonon-mediated pairing in the hole-doped cuprates. The curve of vs. carrier concentration can be approximated by an inverted parabola with the maximum value of occurring at an optimal dopant concentration x (Uchida 1993). (Note that the terminology under-doped refers to values of x smaller than the optimally-doped value Xo, whereas over-doped refers values of x larger than Xo.) The isotope effect on Tc for optimally-doped material is essentially zero (i.e., Tc a with a wO M = ion mass) (Franck 1994). 

An example of the features in Pab(T) that are associated with the pseudogap can be seen in the Pab T) data displayed in figs. 8a and 1 la for the Yi j Pr cBa2Cu307 5 system. As the system becomes more under-doped with increasing x, PabiX) deviates fi om linear behavior at higher temperature at a characteristic temperature T which represents a crossover into the pseudogap state at T < T. ... 

HC=C-C=CH It was found that the simplest diacetylene, butadi-yne, can be polymerized spontaneously and mildly in DCA and apoCA canals at temperatures ranging from -20°C to 30°C. The polymerization was accompanied by a sequence of colour change from colorless through violet and brown to finally yield a black material with a metallic luster. The resulting polymers are characterized by infrared and Raman spectroscopies as having a polyconjugated main chain by 1,4-addition. The electric conductivity of the polymers in the inclusion state and of the separated polymers were about 10 "7 to 10 S/cm under doping with iodine at room temperature [15]. 

H2C=CH—CH-CH X (X Cl, Br) 1-Chloro- or 1-bromo-l,3-butadiene can be polymerized in DCA and apoCA canals to yield polymers with 1,4-trans structure. Since the separated polymers from the hosts are soluble in chloroform, they serve as precursors for polyacetylene. The dehydrohalogenation from the precursor polymer occurred slowly at room temperature and rapidly over 150°C in an atmosphere of dry nitrogen, accompanying a colour change from light yellow through brown to finally yield a black material with a metallic luster. The electric conductivity was about 10 s/cm under doping with iodine [16]. 

H2C=CX(CN) (X Cl, Br) The polymerization of 2-chloroacrylo-nitrile in DCA and apoCA canals was carried out in a way similar to that in case of butadiene derivatives. The dehydrochlorination of the polymer in the canals occurred gradually on heating at 140°C without adding an acceptor. The conversion in a DCA canal amounted to 70 % after one day. The electric conductivity of the polymer in the inclusion state was about 10 S/cm under doping with iodine at room temperature [17]. 

Fig. 31.36 XPS spectrum of the passive iron oxide layer formed on steel under doped polyaniline coating. (From Ref. 26.)...

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