Because the charge carriers (electrons in n-type or holes in p-type semiconductors) transport both heat and charge, κ E is commonly estimated using the measured σ using the Wiedemann-Franz law: κ E = LσT , where L is the Lorenz number.
What is Lorenz number value?
The Lorentz number is a dimensionless number that relates the thermal conductivity of a metal to its temperature and its electrical conductivity. The Lorentz number equals voltage squared times specific electrical conductivity divided by the temperature difference and specific thermal conductivity .
How do you calculate lattice thermal conductivity?
The final lattice thermal conductivity can be written as [20], [37], (6) κ αβ = 1 k B T 2 Ω N ∑ λ f 0 ( f 0 + 1 ) ( ħ ω λ ) 2 v λ α F λ β where Ω and N are the volume of the unit cell and the number of q points in the Brillouin zone (BZ).
What is the expression for Wiedemann Franz law?
The usual statement of the Wiedemann–Franz law is, Kσ=LT . Here K is the electrical component of the thermal conductivity, σ is the thermal conductivity, T is the absolute temperature, and L is the Lorentz number.
What is the ratio of thermal conductivity to electrical conductivity?
In physics, the Wiedemann–Franz law states that the ratio of the electronic contribution of the thermal conductivity (κ) to the electrical conductivity (σ) of a metal is proportional to the temperature (T) .
What is lattice thermal conductivity?
Lattice thermal conductivity (κ) is one of the most important thermoelectric parameters in determining the energy conversion efficiency of thermoelectric materials . However, thermal conductivity calculations are time-consuming in solving the Boltzmann transport equation or performing the molecular dynamic simulations.
Are Diamonds heat resistant?
At high pressure (~20 GPa) diamond can be heated up to 2500 °C, and a report published in 2009 suggests that diamond can withstand temperatures of 3000 °C and above . Diamonds are carbon crystals that form deep within the Earth under high temperatures and extreme pressures.
Which has highest thermal conductivity?
Along with its carbon cousins graphite and graphene, diamond is the best thermal conductor around room temperature, having thermal conductivity of more than 2,000 watts per meter per Kelvin, which is five times higher than the best metals such as copper.
What is the significance of Wiedemann-Franz Lorenz law?
In physics, the Wiedemann–Franz law states that the ratio of the electronic contribution of the thermal conductivity (κ) to the electrical conductivity (σ) of a metal is proportional to the temperature (T) .
What is the ratio of thermal conductivity to electrical conductivity equal to Lorenz number?
The Lorenz number (L) contained in the Wiedemann-Franz law represents the ratio of two kinetic parameters of electronic charge carriers: the electronic contribution to the thermal conductivity (K_el) and the electrical conductivity (sigma), , and can be expressed as LT=K_el/sigma where T is temperature .
What is the unit of thermal conductivity?
The thermal conductivity, K, of a substance is the quantity of heat in calories, or joules, per second passing through a body 1-cm thick with a cross-section of 1 cm 2 when the temperature difference is 1° C. The units are cal/sec/cm 2 /(° C/cm) .
What is the relation between thermal conductivity k and electrical conductivity sigma?
In physics, the Wiedemann–Franz law states that the ratio of the electronic contribution of the thermal conductivity (κ) to the electrical conductivity (σ) of a metal is proportional to the temperature (T) .
What is a good thermal conductivity value?
It is measured in Watts per Metre Kelvin (W/mK). To allow you to get a feel of insulating materials – their thermal conductivity varies between about 0.008 W/mK for vacuum insulated panels (so these are the best, but very expensive!) to about 0.061 W/mK for some types of wood fibre.
How do you find K value for thermal conductivity?
They can be calculated as 1 / (the sum of the resistances of the various layers of the element (its R-values) + the resistance of the internal and external surfaces of the element) .
What factors affect thermal conductivity?
Temperature, moisture content, and density are the most important factors. Other factors include thickness, air velocity, pressing, and aging time. The relationship between main factors with thermal conductivity is presented. Uncertainty about thermal conductivity of insulation materials commonly used.
What is harder than a diamond?
Moissanite , a naturally occurring silicon-carbide, is almost as hard as diamond. It is a rare mineral, discovered by the French chemist Henri Moissan in 1893 while examining rock samples from a meteor crater located in Canyon Diablo, Arizona. Hexagonal boron-nitride is 18% harder than diamond.
