High-resolution soft x-ray photoelectron study of density of states and thermoelectric properties of the Heusler-type alloys(Fe2∕3V1∕3

Abstract

The high-resolution soft x-ray photoelectron study of Heusler͑L2 1 ͒-type ͑Fe 2/3 V 1/3 ͒ 100−y Al y ͑y = 23.8− 25.8͒ alloys directly confirms the correlation between their thermoelectric properties and the electronic structures near the Fermi level. It shows the rigid-band-like shift of the main 3d bands and the increase of the photoelectron intensity at the Fermi edge with the small deviation of the Al content from stoichiometry, i.e., y = 25.0. This implies the existence of the pseudogap across the Fermi level in Fe 2 VAl. The Seebeck coefficients evaluated from the present spectroscopic data agree well with the experimental ones as well as the values estimated from a theoretical density of states in a rigid-band model, while the shift is much smaller than what is expected in the rigid-band model. The small modification of the electronic structure in the offstoichiometric ͑Fe 2/3 V 1/3 ͒ 100−y Al y alloys may be attributed to the lower contribution of Al to the electronic states near E F .

Angle-Resolved Photoemission Analysis of Electronic Structures for Thermoelectric Properties of Off-Stoichiometric Fe_2–xV_1+xAl Alloys

“…To date, theoretical and experimental studies [6][7][8][9] have shown that Fe 2 VAl possesses a nonmagnetic semimetallic electronic band structure with a sharp pseudogap around the Fermi energy E F , as observed in Fig. 1, where the electronic band structure and density of states (DOS) are calculated using the WIEN2k code 10,11) .…”

Origin of large thermoelectric power in off-stoichiometric Fe2VAl-based alloys

“…Figure 1 compares typical valence-band spectra of some of studied alloys. The stoichiometric alloy Fe 2 VAl with small but positive thermoelectric power shows a small shoulder structure at E F in the photoelectron spectrum, indicating the pseudogap predicted for the alloy as having a semimetallic band structure [6]. A small shoulder structure around E F , indicative of the pseudogap, is also recognized for the n-type thermoelectric alloys with the excess V (x > 0).…”

“…Theoretical and experimental studies [3,4] show that an intermetallic compound Fe 2 VAl possesses a sharp pseudogap across the Fermi energy E F , which may lead to the enhancement of the thermoelectric power by changing E F position on partial substitution of the forth element with more or less valence electrons than the original constituent elements without altering the valence-band electronic structure (so-called rigid band model) [5], because the thermoelectric power S(T) at temperature T may depend on the electronic density of states N(E) as follows [6]; ( ) ( )( ) ( ) electron counts per constituent atom (VEC) [5], which can be semi-quantitatively explained by equation (1) [4,6]. However, the off-stoichiometric Fe/V change results in quite different dependence of the thermoelectric power on VEC in a non-rigid-band-like manner and its further enhancement [1,2].…”

Thermoelectric properties of (Fe1−xCox)2VAl Heusler-type compounds

“…When Fe was replaced by V, the conduction shifted from p-type to ntype, while the Seebeck coefficient and low-temperature electrical conductivity increased sharply [7]. Other research showed that the Seebeck coefficient of Fe 2 VAl was also sensitive to Al content [8]. The Seebeck coefficient shifted from −130 to 75 V/K with the deviation of the Al content in (Fe 2/3 V 1/3 ) 100−y Al y (23.8 ≤ y ≤ 25.8) alloys [8].…”