Investigation of carrier scattering process in polycrystalline bulk bismuth at 300 K

Abstract

A carrier scattering process in polycrystalline bismuth at 300 K has been investigated by measuring its Seebeck coefficient, electrical resistivity, magneto-resistivity, Hall coefficient, and Nernst coefficient and solving the Boltzmann equation under the relaxation time and low magnetic field approximations. All measurements were performed using identical bulk bismuth samples; as a result, the scattering process, carrier density, carrier mobility, and Fermi energy were estimated. It was found that acoustic deformation potential scattering was a dominant process even at a temperature of 300 K. In addition, a new measurement method (called a quasi-AC method) was proposed to determine the Nernst coefficient more quickly as compared to the conventional method. It was also shown that the difference in the Nernst coefficients estimated by the two methods affected other material parameters (such as carrier density, mobility, and Fermi energy) only slightly; however, the accurate determination of the Nernst coefficient was required for elucidating the scattering mechanism and estimating the Fermi energy of the studied material.

Temperature dependence of dimensionless figure of merit of a thermoelectric module estimated by impedance spectroscopy

“…5(a) shows the voltage measured at a low frequency f low = ω low /2π = 1 mHz every 2 s, and its impedance Z qAC at 300 K in the suspended condition was measured using the quasi-AC method, which was implemented using a high-precision AC source (Keithley Model 6221) and digital multimeter using real-time data acquisition for the low-frequency region. 22 Here, we applied the suspended condition as the ideal boundary condition to demonstrate our new method. At f low = ω low /2π = 1 mHz, the expected phase angle θ φ would be -0.69 • with 0.72 • uncertainty due to the 2-s sampling time, satisfying θ φ ≥ -1.78 • .…”

“…1 In addition, the Harman method sometimes applies an element and a module to estimate zT. 15 22 by impedance spectroscopy, where the element was suspended by attaching narrow lead wires in vacuum to satisfy the identical boundary condition; 4 however, controlling the temperature of the element and module based on impedance spectroscopy in the suspended condition is very important. Therefore, we have to determine the frequency dependence of the impedance under different boundary conditions to control the temperature and consider how to estimate the temperature-dependent zT of the module properly.…”

Prototype fabrication and performance evaluation of a thermoelectric module operating with the Nernst effect

“…The energy conversion efficiency is not reduced by the heat loss through the metal circuit, as it occurs in a conventional unileg structure of the Seebeck-type modules because the metal circuit formed on the substrate does not pass heat flow from the hot side to the cold side. Moreover, it is also possible to form the P-type structure for the Nernst-type module by controlling the sign of the Nernst coefficient that is not determined by the carrier type but by the carrier scattering mechanism (Jin and Heremans, 2018;Arisaka et al, 2018).…”

“…The contribution of the contact resistance was estimated to be 380 mU, which could be caused by Ag epoxy between the There are other options for obtaining lower electrical contact resistance, such as solder and Wood's metal; however, they easily form eutectic with BiSb alloys. The Nernst thermopower of contaminated BiSb alloys is reduced because the Nernst effect is significantly sensitive to impurities and scattering mechanisms (Arisaka et al, 2018). Ag epoxy was not the best choice, but it was used to produce the Nernst-type module prototype because the purpose of this study is to prove the operation and reveal technical issues.…”

Electrodeposition conditions-dependent crystal structure, morphology and electronic properties of Bi films

“…In the case of the Lorentz mechanism, the magnetoresistance effect is known to be stronger for high-mobility carriers [50,51]. Lorentz magnetoresistance in Bi can be expressed through the characteristics of charge carriers [52][53][54]:…”