Electrical resistivity lattice

Compoun d Stmeture Lattice parameter, pm Density, kg/m Melting point, °C Electrical resistivity, 25°C, n-mx 1Q- Hardness, Mohs scale Microhardness, GPa... 

Superconductivity is the loss of all electrical resistance when a substance is cooled below a certain characteristic transition temperature (Ts). It is thought that the low temperatures are required to reduce the effect of the vibrations of the atoms in their crystalline lattice. Superconductivity was first observed in 1911 in mercury, for which Ts = 4 K. Over the years, many other metallic superconductors were identified, some having transition temperatures as high as 23 K. However, low-temperature superconductors need to be cooled with liquid helium, which is very expensive. To use superconducting devices on a large scale, higher transition temperatures would be required. 

Homogeneous alloys of metals with atoms of similar radius are substitutional alloys. For example, in brass, zinc atoms readily replace copper atoms in the crystalline lattice, because they are nearly the same size (Fig. 16.41). However, the presence of the substituted atoms changes the lattice parameters and distorts the local electronic structure. This distortion lowers the electrical and thermal conductivity of the host metal, but it also increases hardness and strength. Coinage alloys are usually substitutional alloys. They are selected for durability—a coin must last for at least 3 years—and electrical resistance so that genuine coins can be identified by vending machines. 

Grayish metal hexagonal close-packed crystal system, lattice constant, a=2.286 A and c=3.584 A density 1.85 g/cm permeable to x-rays highly ductile modulus to weight ratio very high, elastic modulus 44.5 x 10 at 25°C (for hot-pressed block and sheet) melting point 1,287°C vaporizes at 2,471°C sound transmission velocity 12,600 m/sec reflectivity (white hght) 55% thermal neutron absorption cross-section 0.0090 barns/atom electrode potential, Be/Be2+(aq) 1.85 V electrical resistivity 3.36 x 10-i° ohm.m (at 20°C). 

Soft silvery metal body-centered cubic crystal lattice density 5.24 g/cm melts at 822°C vaporizes at 1,596°C electrical resistivity 81 microhm-cm reacts with water soluble in liquid ammonia. 

YeUow metal face centered cubic crystals lattice constant, a at 25°C 4.0786A density 19.3 g/cm hardness 2.5-3.0 (Mohs), 18.5 (BrineU) melts at 1,064°C vaporizes at 2,856°C electrical resistivity 2.051 microhm-cm at 0°C and 2.255 microhm-cm at 25°C Young s modulus 11.2x10 psi at 20°C (static) Poisson s ratio 0.52 thermal neutron capture cross section 98.8 barns insoluble in almost all single acids or hydroxide solutions dissolves in aqua regia. 

Silvery-white metal close-packed cubic crystals lattice constant 3.8394A at 20°C density 22.42 g/cm (highest among metals) melts at 2410°C vaporizes at 4,130°C hardness 6-6.5 Mohs electrical resistivity 4.71 j,ohm-cm Young s modulus 3.75 x 10 tons/in magnetic susceptibility 0.133 x 10 cm3/g thermal neutron absorption cross section 440 barns. 

Gray, heavy, and very hard metal malleable and ductile body-centered cubic lattice structure the density of the metal 16.65 g/cm at 20°C and that of powder 14.40 g/cm melts at 2,996°C vaporizes around 5,458°C electrical resistivity 13.1 microhm-cm at 25°C modulus of elasticity 27x10 psi Poisson s ratio 0.35 magnetic susceptibility 0.849x10 cgs units at 25°C insoluble in water, alcohol and practically all acids soluble in hydrofluoric acid... 

It is the scattering of conduction electrons by the lattice vibrations, phonons, which produces electrical resistance at room temperature. (At low temperatures, it is... 

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). 

ZT Y r A A A A A AC dimensionless thermoelectric figure of merit electronic coefficient of heat capacity (1+ZT)F2 crystal field singlet non-Kramers doublet (crystal field state) crystal field triplet crystal field triplet hybridization gap jump in heat capacity at Tc K KL -min P 6>d X JCO total thermal conductivity of solid thermal conductivity of electrons or holes thermal conductivity of lattice minimum lattice thermal conductivity electrical resistivity Debye temperature magnetic susceptibility magnetic susceptibility at T = 0... 

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