Amorphous electric resistivity

Physical properties of a-crystaUine metallic arsenic are given in Table 1. The properties of P-arsenic are not completely defined. The density of P-arsenic is 4700 kg/m it transforms from the amorphous to the crystalline form at 280 °C and the electrical resistivity is reported to be 107 H-cm. 

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

CdSe, CdTe. CdSe films have been grown from complexed (with tartaric acid and triethanolamine) cadmium acetate or cadmium sulfate solutions and sodium selenosullale.1272 81 84 The films were amorphous or nanocrystalline with an average crystallite size of 6nm. The optical band gap was 1.8-2.1 eV, and the electrical resistivity was of the order 104-106Qcm. 

Silvery-white, brittle metallic element crystal system-hexagonal, rhombo-hedral also, exists in two unstable allotropic forms— a yellow modification and a dark-grey lustrous amorphous powder—both of which revert to crystalline form hardness 3.0 to 3.5 Mohs density 6.697g/cm3 melting point 630.5°C boiling point 1635°C electrical resistivity 39.1 microhm-cm at 0°C magnetic susceptibifity —0.87 x 10 emu/g. 

Steel-gray crystalline brittle metal hexagonal crystal system atomic volume 13.09 cc/g atom three allotropes are known namely, the a-metaUic form, a black amorphous vitreous solid known as P-arsenic, and also a yellow aUotrope. A few other allotropes may also exist but are not confirmed. Sublimes at 613°C when heated at normal atmospheric pressure melts at 817°C at 28 atm density 5.72 g/cc (P-metallic form) and 4.70 g/cm (p-amor-phous form) hardness 3.5 Mohs electrical resistivity (ohm-cm at 20°C) 33.3xlCh (B—metallic polycrystalline form) and 107 (p—amorphous form) insoluble in water. 

Black hard solid or brownish black amorphous powder also occurs as tetragonal, a-rhombohedral and P-rhombohedral crystal forms density 2.34 g/cm3 (crystal), 2.45 g/cm (amorphos powder) hardness 9.3 Mohs melts at 2,075°C vaporizes at 4,000°C electrical resistivity 3,000,000 ohm-cm at... 

Belertser et al (1988) have observed that the electrical resistivity of amorphous chromium films at liquid-helium temperatures jumps from a value (10 3 O cm) characteristic of a poor metal by a factor 103, when the hydrogen content is increased sufficiently to increase the lattice constant by 10%. The transition is not abrupt, and is thought by these authors to be of Anderson type. They claim that it is the first time such a transition has been observed in a solid, and that it is similar to that in expanded mercury vapour (Section 4). 

Electrical. Unlike their crystalline counterpans, amorphous metals generally have high electrical resistivity not only at room temperature, hut also, because of a very small temperature coefficient, near absolute zero. Cenain metallic glasses, e.g.. La, Au <,. do show superconductivity. 

Another amorphous phase of carbonitride, C N phase with sp bonding, was shown to be a stable phase which exhibits high electrical resistivity and thermal conductivity similar to that of diamond-like films. The diamond-like properties and non-diamond-like bonding make C N an attractive candidate for applications such as thermal management in high-performance microelectronics. 

When the formulated solution predominantly contains polyols, sugars, or polymers, the interstitial phase does not usually crystallize out upon cooling but increases progressively in viscosity as a glass-like system. In the case where the interstitial phase has effectively the structure of a glass, the frozen system becomes fully rigid once the glass transition temperature (Fg) is reached. In contrast, some amorphous systems may show no such definite transition, but they eventually become very stiff at low temperature, as shown by electrical resistance studies. 

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