Thermoelectric materials should have a high Seebeck coefficient
and thermal resistivity to maximize the Peltier effect and low electric resistivity to minimize Joule effect losses.
and resistivity are measured simultaneously with a ZEM-3 (M10) ULVAC system, supplied with Pt electrodes, in the range T = 30[degrees]-350[degrees]C and 950 mBar oxygen pressure.
In 1911, Altenkirch proposed that dimensionless figure of ZT value can represent performance of thermoelectric materials and pointed out that when the ZT value reached 3 , thermoelectric conversion technology can compete with conventional power generation technology; ZT = [a.sup.2][sigma]T/[lambda], where [alpha], [sigma], and [lambda] are, respectively, Seebeck coefficient
(thermoelectric power), electrical conductivity, and thermal conductivity of the thermoelectric material and T is the thermodynamic temperature.
The Seebeck coefficient
(S) measurement as a function of time is one of the significant methods to analyze electronic properties of solids.
As such, the Seebeck coefficient
has been estimated as the slope of the curve, neglecting any second-order effect.
where the V is the produced open voltage, T is the temperature at the junctions, [[alpha].sub.A] and [[alpha].sub.B] are the absolute Seebeck coefficient
of each conductor, and [[alpha].sub.AB] is the Relative Seebeck Coefficient
Powder samples for overall conductivity and Seebeck coefficient
measurements were axially pressed into rectangular bars of 18 x 3 x 2 [mm.sup.3] at 50 MPa and sintered at 1150[degrees]C for 24 h in air.
The performance of thermoelectric devices is determined by the dimensionless figure of merit (ZT), expressed in ZT = [S.sub.2]T/[rho]K, where S is the Seebeck coefficient
, T is the absolute temperature, p is the electrical resistivity, and [kappa] is the total thermal conductivity.
Typical thermocouples (TCs) are made from two different conductors, one with a large positive Seebeck coefficient
and the other with a large negative coefficient-- for example, iron at +18.9 [micro]V/[degrees]C and constantan at -35 [micro]V/[degrees]C in a type J TC.
The fabricated thermopiles typically have a resistance of 20 K[OMEGA] and showed a Seebeck coefficient
of 7.14 [micro]V [(mK).sup.-1].
According to (3), the voltage of thermoelectric is related to the Seebeck coefficient
a, the temperature difference between hot and cold sides ([T.sub.h] - [T.sub.c]), the electric current of thermoelectric I, and the thermoelectric resistance R.