Effect of Zn-Doping on the Phase Transition Behavior and Thermoelectric Transport Properties of Cu2Se

Abstract

<jats:p>We report on the phase transition behavior and thermoelectric transport properties of Zn-doped Cu&lt;sub&gt;2&lt;/sub&gt;Se. Cu&lt;sub&gt;2&lt;/sub&gt;Se is comprised of nontoxic, low-cost and abundant elements, and has been attracting attention because of its very high thermoelectric performance, &lt;i&gt;ZT&lt;/i&gt;, at high temperatures. Many studies have reported enhanced &lt;i&gt;ZT&lt;/i&gt; in impurity doped Cu&lt;sub&gt;2&lt;/sub&gt;Se, however, little is known about the effect of dopants on the phase transition behavior of Cu&lt;sub&gt;2&lt;/sub&gt;Se. In this study, we prepared (Cu&lt;sub&gt;1-x&lt;/sub&gt;Zn)&lt;sub&gt;2&lt;/sub&gt;Se (x = 0 ~ 0.03) compounds by spark plasma sintering, and investigated the phase transition behavior in terms of the temperature-dependent thermoelectric transport properties. Undoped Cu&lt;sub&gt;2&lt;/sub&gt;Se consists of monoclinic α-Cu&lt;sub&gt;2&lt;/sub&gt;Se and berzelianite at room temperature. However, the crystal structure of (Cu&lt;sub&gt;1-x&lt;/sub&gt;Znx)&lt;sub&gt;2&lt;/sub&gt;Se compounds is changed into a single phase of α-Cu&lt;sub&gt;2&lt;/sub&gt;Se with increasing Zn content. As the Zn content increased, electrical conductivity decreased and Seebeck coefficient increased due to the donor role of Zn. The phase transition temperatures of the compounds were characterized as a function of Zn content, based on the temperature-dependent electrical conductivities and Seebeck coefficients. The phase transition temperature was increased by increasing Zn content, and it was attributed to the disappearance of the berzelianite phase whose phase transition temperature is lower than that of α-Cu&lt;sub&gt;2&lt;/sub&gt;Se. Detailed effects of Zn-doping on both the phase transition behavior and thermoelectric transport properties were discussed.</jats:p>

Cu2−xS and Cu2−xSe Alloys: Investigating the Influence of Ag, Zn, and Ni Doping on Structure and Transport Behavior

“…This parameter takes values around 10 µVK −1 at RT and increases practically linearly to around 60-70 µVK −1 at 750 K. The presence of dopants and/or additional phases has a similarly marginal effect here, with a tendency for lower α values for doped systems (Figure 8). This may be associated with both an increase in charge carrier concentration and further defect formation in the cationic sublattice with successive measurement cycles, suggesting significantly lower stability of Cu 1.8 Se than Cu 1.97 S. Once again, this result contradicts literature reports, where zinc or nickel dopants result in an increase in recorded Seebeck coefficient values [13,54]. However, there is a possibility that this slight decrease should be correlated with an increasing contribution of minority charge carriers.…”

“…Meanwhile, the only dopant that significantly affects the reduction of the lattice component and total λ (particularly in high-temperature regions) is zinc, confirming our earlier statements that it is probably the only dopant that incorporates into the structure of this material providing additional centers for lattice phonons scattering. Furthermore, this material also exhibits a reduction in the λ e , which is confirmed by studies on zinc doping of the stoichiometric system [13,14,54]. Slightly reduced λ e and total λ were also expected for nickel doping [13].…”

“…This is particularly important due to the cyclic nature of the operational conditions of TE materials (heatingcooling), which is often overlooked by many authors, neglecting to address the material's properties after subsequent cycles. Given the well-studied properties of doped Cu 2 Se characterized by cubic structure [13,14,43,54], this study focuses on doping the single-phase Cu 1.8 Se system. After sintering, the copper(I) sulfide, Cu 1.97 S, completely transitioned into a monoclinic structure with significantly shifted respective reflections toward lower counts (Figure 3a), suggesting enlarged lattice parameters caused, most probably, by non-stoichiometry on the cationic sublattice (Table S2).…”

“…In this case, the presence of dopants does not result in a deterioration of the ZT parameter; on the contrary, it rather improves ZT, showing increasingly better properties with each subsequent cycle, suggesting material relaxation during operating conditions. However, these materials still remain a relatively poor group of candidates for thermoelectric applications, unlike the indications from the literature for doped Cu 2 Se [13,43,54].…”

Efficient photo-assisted Fenton-like reaction of yolk–shell CuSe(Cu2Se)/g-C3N4 heterojunctions for methylene blue degradation

“…Copper selenide is a wideband p-type semiconductor 11 with unique thermoelectric, 21 Seebeck, 22 and photo-electric 23 effects and is widely applied to solar cells 24 because of adjustable stoichiometric ratios (CuSe, Cu 2 Se, Cu 3 Se 2 , and Cu 2−x Se) [12][13][14][15] and different types of crystallographic systems: cubic, tetragonal, single monocline, and hexagonal structures. [16][17][18][19][20] In addition, copper selenide quantum dots have been used in traditional photocatalysis because of their high specic surface area, crystallinity, and small particle size. 25 Similar to traditional iron ions, copper ions generate highly active hydroxyl radicals (cOH) by reacting with hydrogen peroxide (H 2 O 2 ).…”