Unipolar conduction

AU these features—low values of a, a strong temperature dependence, and the effect of impurities—are reminiscent of the behavior of p- and n-type semiconductors. By analogy, we can consider these compounds as ionic semiconductors with intrinsic or impurity-type conduction. As a rule (although not always), ionic semiconductors have unipolar conduction, due to ions of one sign. Thus, in compounds AgBr, PbCl2, and others, the cation transport number is close to unity. In the mixed oxide ZrOj-nYjOj, pure 0 anion conduction t = 1) is observed. 

Because of the high values of conductivity which in individual cases are found at room temperature, such compounds are often called superionic conductors or ionic superconductors but these designations are unfounded, and a more correct designation is solid ionic conductors. Strictly unipolar conduction is typical for all solid ionic conductors in the silver double salts, conduction is due to silver ion migration, whereas in the sodium polyaluminates, conduction is due to sodium ion migration. 

For unipolar conduction and for a single conduction mechanism, i.e., for identical charge carriers,... 

As a rule (though not always), ionic semiconductors have unipolar conduction because of ions of one sign. Thus, in compounds AgBr, PbCl2, and others the cation transport number is close to unity. In the mixed oxide Zr02 nY20 pure anion conduction = 1) is observed. 

Strictly unipolar conduction is typical for all solid ionic conductors in the silver double salts, conduction is because of silver ion migration, while in the sodium polyaluminates, conduction is because of sodium ion migration. 

The empirical phase of the development of solid electrolyte fuel cells was overcome only after many general advances in research on solids. These included development of X-ray structure analysis, new knowledge on the ion conduction of solids from the measurements of transport numbers by Tubandt (first detection of unipolar conduction by anions), the establishment of the theory of disorder in solids by Frenkel, Schottky, Wagner and Jost, and the development of isotope methods for the investigation of diffusion processes in solids. 

In comparison to the research in n-type oxide semiconductors, little work has been done on the development of p-type TCOs. The effective p-type doping in TCOs is often compensated due to their intrinsic oxide structural tolerance to oxygen vacancies and metal interstitials. Recently, significant developments have been reported about ZnO, CuA102, and Cu2Sr02 as true p-type oxide semiconductors. The ZnO exhibits unipolarity or asymmetry in its ability to be doped n-type or p-type. ZnO is naturally an n-type oxide semiconductor because of a deviation from stoichiometry due to the presence of intrinsic defects such as Zn interstitials and oxygen vacancies. A p-type ZnO, doped with As or N as a shallow acceptor and codoped with Ga or Zn as a donor, has been recently reported. However, the origin of the p-type conductivity and the effect of structural defects on n-type to p-type conversion in ZnO films are not completely understood. 

It can be readily shown that for a volume of unipolar and uniformly distributed charged particles bounded by a conductive surface equidistant from a center of symmetry [either a plane (flat volume) a line (cylindrical volume) ... 

Electrical conductivity measurements on silicate melts indicate an essentially ionic conductivity of unipolar type (Bockris et al., 1952a,b Bockris and Mellors, 1956 Waffe and Weill, 1975). Charge transfer is operated by cations, whereas anionic groups are essentially stationary. Transference of electronic charges (conductivity of h- and n-types) is observed only in melts enriched in transition elements, where band conduction and electron hopping phenomena are favored. We may thus state that silicate melts, like other fused salts, are ionic liquids. 

Zarate and his collaborators (301) conducted a systematic follow-up study, evaluating the number of hospitalizations in the 5 years before clozapine compared with the rehospitalization rate while on this agent. These authors found that monotherapy with clozapine reduced both the number of episodes and rehospitalizations in 17 previously severely ill affective patients. The yearly rate before clozapine was 0.8 1.2 and after clozapine 0.4 1.2, a difference that was statistically significant. Rehospitalization rates were lowest in the schizophrenic, schizoaffective bipolar, and schizoaffective depressed patients, whereas unipolar and bipolar depressed patients had the highest relapse rate. 

It has been shown that the EL of polysilane-based LEDs is emitted near the interface between the polysilane and the electron injecting electrode, because of the strong unipolar (hole conductive) nature of polysilanes. Defect levels existing at the interface are considered to play an essential role in the emission of EL in the visible region,93 and have both positive and negative effects on the LED characteristics. The positive space charges generated by... 

The majority of unipolar ionic conductors identified to date are polymorphic compounds with several phase transitions, where the phases have different ionic conductivities owing to modifications in the substructure of the mobile ions [28], One of the first studied cationic conductors was a-Agl [21]. Silver iodide exhibits different polymorphic structures. Agl has a low-temperature phase, that is, [3-Agl, which crystallizes in the hexagonal wurtzite structure type, and a high-temperature cubic phase, a-Agl, which shows a cubic CsCl structure type [20,22] (see Section 2.4.5). 

Multipolar neurons have many processes and serve principally as motor neurons. Motor neurons, efferent because they conduct impulses away from the central nervous system (the brain and spinal cord) regulate the function of muscles and glands. Afferent neural pathways that send signals to the (CNS) are generally composed of unipolar neurons. Unipolar neurons also serve as sensory neurons— their filamentous dendritic processes exposed and elaborated into or connected to sensory receptor cells. Intemeurons are neurons that connect neurons along a neural pathway. 

Dc arc spectrography is still a most powerful method for trace determinations in solids even with difficult matrices such as U3Og. Here the detection limits for many elements are down in the sub-pg/g range [358]. It is still in use for survey analysis, especially in the case of ores, minerals and geological samples. In work with unipolar arcs, re-ignition of the arc is often facilitated by providing an hf discharge over the dc arc, by which the arc channel is kept electrically conductive. 

Figure 3. Schematic of electrohydrodynamic conditions in unipolar and bipolar conduction.

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