Electrical resistivity under pressure

In this section, as examples of pressure-induced crossover, we will show some data on electrical resistivity under pressure for three HF materials CeAla, CeAL, and CeInCu2. Brief discussions about these novel electronic states induced by high pressure will be introduced. 

Wang, P. Ding, T., Creep of Electrical Resistance Under Uniaxial Pressures for Carbon Black-Silicone Rubber Composite. J. Mater. Sci. 2010, 45, 3595-3601. 

A similar unit, modified in details such as location of condenser, use of an agitator and shape of the vessel, was used by Fisher and Whitney . Further substantial modifications to permit interface location of specimens, cooling of specimens and operation under applied pressure, have been described by Fisher . Earlier laboratory test methods tried by Fisher and Whitney included exposure of specimens heated by their own electrical resistance and of tubular specimens containing a pencil-type resistance-wire heater in a quartz tube. 

Fig. 5.59 shows a section through a Piezo-resistive silicon pressure sensor. The ambient pressure is applied from above, while the pressure being measured is applied from below. A silicon membrane that deforms under the pressure is applied to a silicon carrier structure. Piezo-resistive structures are fitted in the membrane, which then change their resistance accordingly when the membrane deforms. A bridge circuit generates an electrical output signal which is proportional to the difference in pressure. 

The Physical Properties are listed next. Under this loose term a wide range of properties, including mechanical, electrical and magnetic properties of elements are presented. Such properties include color, odor, taste, refractive index, crystal structure, allotropic forms (if any), hardness, density, melting point, boiling point, vapor pressure, critical constants (temperature, pressure and vol-ume/density), electrical resistivity, viscosity, surface tension. Young s modulus, shear modulus, Poisson s ratio, magnetic susceptibility and the thermal neutron cross section data for many elements. Also, solubilities in water, acids, alkalies, and salt solutions (in certain cases) are presented in this section. 

A heliarc-welded, all-nickel can of 850-mL volume was filled with an intimate mixture of NiF, (290 g, 3 mol) and anhyd KF (52 g, 9 mol). The can was valved to a tank of F2 gas and a vacuum pump and was heated by an electric-resistance furnace. The can was heated slowly to 500 C under 10 atm of F2 and then cooled to 250 C, while still under several atm of F2. Several such cycles were carried out before using the device for the regeneration of F2. For the regeneration of F2, the salt was fluorinated at 250 C until no more F2 was taken up. The can was then cooled to 225 C and evacuated to remove the excess F2 and any volatile impurities. The temperature was then raised until the desired F, pressure (at 400 C, 25 atm) was achieved. 

This transition is accompanied by a change in the resistivity of powders, which is measured by means of pressure contacts (Fig. 2b). The total change in resistivity is equal to six orders of magnitude in the density range under investigation and corresponds to a transition from the dielectric state to the metal one. The critical density, i.e., the density at which the transition occurs, is equal to ps2.7-2.9 g/cm according both to diffraction measurements and to electric-resistivity measurements. 

The electric resistance of pure iron increases from 0° C. to a maximum at 757° C., corresponding to the A2 point, and then falls to a minimum at 894° C.—the A3 point. On cooling the reverse changes occur at practically the same temperatures.4 The presence of hydrogen under atmospheric pressure does not materially affect the resistance of the metal up to 920° C.5... 

The solid oxide fue( cell (SOFC) have been under development during several decades since it was discovered by Baur and Preis in 1937, In order to commercialise this high temperature (600 - 1000°C) fuel cell it is necessary to reduce the costs of fabrication and operation. Here ceria-based materials are of potential interest because doped ceria may help to decrease the internal electrical resistance of the SOFC by reducing the polarisation resistance in both the fuel and the air electrode. Further, the possibility of using less pre-treatment and lower water (steam) partial pressure in the natural gas feed due to lower susceptibility to coke formation on ceria containing fuel electrodes (anodes) may simplify the balance of plant of the fuel cell system, and fmally it is anticipated that ceria based anodes will be less sensitive to poising from fuel impurities such as sulphur. 

The aim is to eliminate entrance effects as much as possible and any influence on the flow of the pressure tap holes into the channels. This was achieved by integrating on the same silicon chip the microchannel, the pressure taps and the pressure sensors. The fabrication process and the operating mode are described in [28]. The pressure sensors are constituted cf a membrane which is deformed under the fluid pressure and on which is deposited a thin film strain gauge. This strain gauge forms a Wheatstone bridge whose the membrane deformation modifies the electrical resistances. 

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