P-type conductor

LaMn03 is an intrinsic p-type conductor. Electronic conductivity is enhanced by substitution of the La3+ site with divalent ions such as strontium or calcium. Of the alkaline-earth dopants, Sr substitution is preferred for SOLC applications because the resultant perovskite forms stable compounds with high conductivity in the oxidizing atmosphere found at the cathode [41], Extensive data show that La, xSi. MnO where x = 0.1 - 0.2, provides high conductivity while maintaining mechanical and chemical stability with YSZ [41, 42],... 

Lanthanum chromite is a p-type conductor so divalent ions, which act as electron acceptors on the trivalent (La3+ or Cr3+) sites, are used to increase the conductivity. As discussed above, the most common dopants are calcium and strontium on the lanthanum site. Although there is considerable scatter in the conductivities reported by different researchers due to differences in microstrucure and morpohology, the increase in conductivity with calcium doping is typically higher than that with strontium doping [4], The increase in conductivity at 700°C in air with calcium additions is shown in Figure 4.1 [1, 2, 28-44], One of the advantages of the perovskite structure is that it... 

Would doping of poly acetylene with (a) Rb, (b) H2SO4 give an rt-type or a p-type conductor ... 

Extrinsic Semiconductors. Impurity levels can be either donor levels near the empty zone (normal or n-type), or acceptor levels near the filled band (abnormal or p-type). Conductivity in n-type conductors will be due to electrons in the empty band donated by the impurity levels, and in p-type conductors, to positive holes in the previously filled band, arising from the transition of electrons to the impurity acceptor levels. 

The second step will be a desorption of the chemisorbed oxygen 4- 2O < 02 " (p-type conductor)... 

The conductivities of LSFTO at different partial pressures of oxygen were extracted from the dc conductivities. The conductivities systematically increase with increasing pQ indicating that the compound is a p-type conductor in this pQ region. At 900°C, the slope of the log-log plot is — 1 /4 as expected. As the temperature decreases, the slopes decrease until they reach a value of 1 /6 at 500°C. Data obtained at lower p0 are discussed below. 

In the case of NiO which is p-type metal-deficient material we have a structure with Ni2+, O2- and Ni3+ in nickel vacancy sites. Addition of lithium ion impurity to NiO makes it a p-type conductor and oxide growth rate is reduced compared with the Ni-02 system alone. On the other hand addition of Cr to Ni results in greater ease of oxidation than nickel alone due to higher cation diffusivity. 

Figure 6. Three experimental examples of Kroger-Vink diagrams in a pure oxide MO with ideal defect chemistry SnOj as n-type conductor, PbO as mixed conductor and La2Cu04 as p-type conductor.45 (Reprinted from J. Maier, Ionic and Mixed Conductors for Electrochemical Devices, Radiat. Eff. Defects Solids, 158, 1-10. Copyright 2003 with permission from Taylor Francis.)...

There has been some work on the electrical characterisation of transparent p-type conductors, particularly Cul and CuSCN (Tennakone et al, 1998a, b). However, the characterisation focused on continuous thin films rather than on structured layers. For CuSCN, HaU mobilities of the order of 20 cm V s have been reported and similar values were found in Cul films (Rost, 1999), indicating that both materials are well-suited for device applications. So far, however, solar cells involving these materials with efficiencies beyond have not been reported. Both materials, CuSCN and Cul, have rather high diffusion coefficients for Cu diffusion. These findings raise the question if stable devices can be fabricated, or if Cu migration and diffusion effects may render thin-film devices inherently instable. 

PPV and its alkoxy derivatives are p-type conductors and, as a consequence, hole injection is more facile than electron injection in these materials. Efficient injection of both types of charge is a prerequisite for efficient LED operation. One approach to lowering the barrier for electron injection is the use of a low work function metal such as calcium. Encapsulation is necessary in this instance, however, as calcium is degraded by oxygen and moisture. An alternative approach is to match the LUMO of the polymer to the work function of the cathode. The use of copolymers may serve to redress this issue. 

For the investigation of the electronic character of catalytic reactions, it has been found fruitful to study not only the catalytic action of metals and semiconductors of known electron state distribution, but also the changes of this distribution by illumination during catalysis. The War-burg-Barcroft technique of biochemistry has proved to be very suitable for this purpose. It could be shown in a semiquantitative way that promotion of electrons enhances acceptor reactions, that electron traps hinder such action, and that n-type and p-type conductors behave in opposite fashion when employed as photocatalysts. Using ferrites as catalysts in an acceptor reaction, the electron transfer concept was confirmed. 

When replacing the Kquid electrolyte in dye-sensitized solar cells with a sohd p-type conductor, a range of requirements have to be fulfilled to preserve the high external quantum efficiencies common to the original photoelectrochemical devices. 

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