Thermionic energy conversion based on 3D Dirac semimetals

Abstract

First, we investigate theoretically the thermionic emission from three-dimensional Dirac semimetals (3D DSs), then we explore their practical application as the cathode of a thermionic energy generator (TIEG). Based on the linear energy dispersion around Dirac points, we derive the generalized analytical formula of the thermionic emission from 3D DSs through the Dirac Hamilton, which is significantly different from the Richardson–Dushman (RD) law for metallic materials. The reason for this originates from the fact that electrons behave like massless fermions and follow ultrarelativistic quasiparticle dynamics in 3D DSs, deviating from the nonrelativistic electrons with a parabolic energy dispersion in conventional metal materials. We develop a theoretical model of the solid-state thermionic energy generator using 3D DSs as the cathode and obtain its optimal working regions at different temperatures. For a 3D DS-based cathode at 1400 K, the maximum efficiency of the proposed TIEG can reach 50.0%, where the correspondingly optimal work functions of the cathode and anode are 2.05 eV and 0.612 eV, respectively. The results presented in this work demonstrate that 3D DSs are superior to metallic materials and graphene in thermionic application, and will contribute to the choice of electrode materials, optimal designs, and control operative conditions of practical TIEGs.

Two-Dimensional Surface Topological Nanolayers and Dirac Fermions in Single Crystals of the Diluted Magnetic Semiconductor (Cd1−x−yZnxMny)3As2 (x + y = 0.3)

“…This is realized by topological states, which make 3D cadmium arsenide an analogue of a graphene and to be related to the group of Dirac semimetals, which are materials having a linear dispersion law in all three directions of the momentum space. Relatively small effective mass of the electrons and their super high mobility have recently been allowed to realize on the base of cadmium arsenide the series of promising prototypes for electronics: the high responsivity and ultrafast wide range photodetector [3], Seebeck-effect-based thermoelectric devices [4], a solid-state demultiplexer or a digital magnetic field direction sensor [5], a high-temperature thermionic generator [6], terahertz plasmonic devices [7], and a multifunctional nanosized p-n junction [8]. There is an interesting and helpful opportunity to form continuous series of solid solutions in the Cd 3 As 2 -Zn 3 As 2 system, which can, in turn, allow one to successively change physical properties of the Cd 3 As 2 -Zn 3 As 2 (CZA) solid solutions via varying in the ratio of end members, including changing in both the type of conductivity (from nto p-conductivity) and the band gap (from~0.1 eV to~1.0 eV) [9].…”

Progress Toward High Power Output in Thermionic Energy Converters

“…However, recent analytical derivations have asserted that graphene sheets and other select materials such as 3D Dirac semimetals may exhibit a pre-factor temperature dependence of J ≈ T 3 . [122][123][124][125][126][127][128][129] Several researchers have proposed that this enhanced temperature dependence could prove advantageous if such materials were used as emitters in TECs. [122,126,128,129] However, we are aware of only a single dataset [130] that has been used to experimentally validate this enhanced temperature dependence, [122,124] and we are unaware of any TEC prototypes that have been created to demonstrate this concept.…”

“…[122][123][124][125][126][127][128][129] Several researchers have proposed that this enhanced temperature dependence could prove advantageous if such materials were used as emitters in TECs. [122,126,128,129] However, we are aware of only a single dataset [130] that has been used to experimentally validate this enhanced temperature dependence, [122,124] and we are unaware of any TEC prototypes that have been created to demonstrate this concept. In addition, the derivations of this enhanced emission [122,124,129] typically consider the density of electron states in the material alone, rather than considering the maximum current density possible in the vacuum; this can in some cases yield higher-than-feasible emission current densities.…”

“…[122,126,128,129] However, we are aware of only a single dataset [130] that has been used to experimentally validate this enhanced temperature dependence, [122,124] and we are unaware of any TEC prototypes that have been created to demonstrate this concept. In addition, the derivations of this enhanced emission [122,124,129] typically consider the density of electron states in the material alone, rather than considering the maximum current density possible in the vacuum; this can in some cases yield higher-than-feasible emission current densities. [13,39] Additional experimental investigations and proof-of-concept prototypes are needed to evaluate the feasibility of this approach.…”

Thermionic enhanced heat transfer in electronic devices based on 3D Dirac materials

“…A 3D Dirac semimetal phase with a linear energy-momentum dispersion has been experimentally observed in Cd 3 As 2 by means of angle-resolved photoemission spectroscopy 9 . The material has attracted considerable attention [10][11][12][13] and has been found to have many astounding properties such as the extraordinarily high mobility of electrons (10,000 cm 2 /V s at room temperature) 14 , tunable mid-infrared optical switching 15 , low thermal conductivity 16 and high efficiency and non-Richardson thermionics 17,18 . By using the linear energy-momentum dispersion, the thermionic emission of Dirac materials is determined to be 17…”