Pressure Dependence of the Electrical Conductivity

The electrical d.c. resistivity of SmSe single crystals at room temperature as a function of hydrostatic pressure is shown in Fig. 62. The filled circles at 37, 41, 52, and 70 kbar, corresponding to 172,115, 69, and 62 xQ cm, respectively, are deduced from spectroscopical data, Welber, Jayaraman [7]. Similar q versus P curves up to 50 kbar showing a continuous change of Q versus P are given in the papers of Jayaraman et al. [3], Bucher et al. [12], and in the reviews of Jayaraman [13,14,15], and Jayaraman et al. [16]. 

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Figure 16. Oxygen partial pressure dependence of the electrical conductivity of doped Ce02. The steep decrease is due to excess electrons, the flat behavior to oxygen vacancies. If we refer to typical oxygen partial pressures in an SOFC, viz. to 10" bar at the cathode and 0.2 bar at the anode, we see that the conductivity changes from ionic into n-type within a high temperature Ce02 based fuel cell. Reprinted from M. Godickemeier and L.J. Gauckler, J. Electrochem. Soc. 145 (1998) 414-421. Copyright 1998 with permission from The Electrochemical Society, Inc.

Calculations based on the above four defect equations prove the oxygen pressure dependence of the electrical conductivity to be Pq, Pq and respectively. 

Atlas and Schlehman have measured the variation of oxygen content and electrical conductivity with oxygen pressure in the temperature range from 1100 to 16(X)°C (87). From the pressure dependence of the electrical conductivity, they inferred that the defects in Pu02 j are constituted of predominantly interstitial plutonium ions, and discussed the change of the form of defects with temperature. However, measurements by the same authors on the density of the PuOj-j. phases (277) led to the conclusion that oxygen vacancies are the predominant defects in the PUO2 phase. 

More recently Chereau and Wadrin (212) have measured the oxygen pressure dependence of the electrical conductivity of PUO2, at 1080°C, and found a dependence of — 1/5, which agrees with the results obtained by Atlas and Schlehman (87). To interpret this, they proposed a divacancy model which yields the dependence of — 1/5. 

Fig. 17. Oxygen pressure dependence of the electrical conductivity of CtjOj at 1200"C (Nagai 1988).

Kanakubo M, Harris KR, Tsuchihashi N, Ibuki K, Ueno M (2007) Temperature and pressure dependence of the electrical conductivity of the ionic liquids 1-methyl-3-octylimidazolium hexafluorophosphate and l-methyl-3-octyl-imidazolium tetrafluorohorate. Fluid Phase Equilih 261 414-420... 

In this case, the number of zinc ions in interstitial positions and the number of free electrons will be decreased by an increase in the partial pressure of oxygen. These disorder reactions result in a dependence of the electrical conductivity on the oxygen pressure. This effect is a well known phenomenon in the field of semiconductors (1). Complicated relations, however, will occur at lower temperatures, at which no equilibrium can be attained between the gas phase and the lattice defects in the whole... 

It has often been pointed out that the electrical conductivity of sintered samples of ZnO and of other n-conducting oxides is frequently caused by the conductivity of thin layers near the surface, and not by the conductivity of the bulk (25-28). According to our present knowledge, these thin layers near the surface of oxides are caused by electron transfer from the layers to the chemisorbate during the chemisorption, and the amount of chemisorption may be related to the electronic properties of the gas molecules and of the solids. The dependence of the electrical conductivity of some semiconductors on the pressure of CO, COj, and on the vapor pressure of ethanol, methanol, acetone, and water, as observed by Ljaschenko and Stepko (29), can be explained by the same mechanism. The dependence of conductivity of some mixed oxides at high temperatures can be explained in a similar way (30). 

Noteworthy in this connection are Muscheid s (39) results on the dependence of the electrical conductivity of single crystals of CdS upon their treatment in vacuo or in oxygen at various pressures. This author observed a strong and sudden decrease of the conductivity when oxygen at... 

Figure 10. Dependence of the electrical conductivity of semiconductive metal oxides on oxygen partial pressure.

The functional dependence of the electrical conductivity of an oxide on the oxygen partial pressure and temperature is shown in Fig. 1.21a. 

Fia. 31. The temperature dependence of the electrical conductivity of chromia at the following conditions (1) oxidized sample in air (2) oxidized sample at 10 Ton-oxygen pressure (3) reduced sample in air (4) reduced sample in 20 Torr of carbon monoxide and (5) reduced sample in 20 Torr of hydrogen (19). 

The conductivity setup was designed for the investigation of the dependence of the electrical conductivity on temperature, current direction relative to the sample, pressure and time in controlled environment (e.g. oxygen, air or vacuum) with high accuracy and reproducibility. In order to meet these requirements, a computer controlled setup was used, which allowed a slow and controlled temperature sweep under reproducible conditions, yielding a high density of acquired data (see chapter 4.1). 

Fig. 1.20. The dependence of equilibrium electric conductivity of ZnO sample on oxygen pressure...

In addition to the dependence on temperature and pressure, the physical properties of seawater vary with the concentration of the dissolved constituents. A convenient parameter for describing the composition is the salinity, S, which is defined in terms of the electrical conductivity of the seawater sample. The defining equation for the practical salinity is ... 

Electrical properties of thin rare earth oxide film have also been studied. The conductivity of praseodymium thin film oxide was measured as a function of temperature and oxygen pressure [9]. The oxide film was found to act as a p-type conduction at temperatures high than 630°C and was a n-type semiconductor at the temperatures of 400-630°C. Thermally evaporated EU2O3 thin film on a glass substrate is also obtained in an amorphous state. From the measurement of frequency dependence of the ac conductance, the predominant mechanism could be ascribed to the result of a hopping type. The ac conductivity measurements were also carried out for thin film of SC2O3 at temperatures between 4 and 295 K [10]. The conductivity was found to obey the relationship of ai(ffl)=Aco which depends on frequency and s is dependent on temperature and is a little lower than unity. By using a classical hop mechanism between randomly distributed localized states, a model was proposed and applied to scandium oxide with the assumption that the localized states are caused by lattice vacancies. The model is expected to be... 

The pressiue dependence of the electrical resistivity of YbCuAl was investigated (Alami-Yadri et al. 1998, 1999a,b) up to 8 GPa. The resistivity at 300 K decreases with increasing pressure. At 8 GPa a dependence occurs at low temperature (Fermi-liquid behavior), and the Kondo temperature decreases with increasing pressure. The experimental setup for these measurements was presented by Jaccard et al. (1998). Furthermore, point-contact spectroscopy was used to measure the interconfigurational excitation energies and conduction-electron lifetime width of valence-fluctuating YbCuAl (Bussian et al. 1982). 

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