Enhanced Thermoelectric Properties of Zr_0.85–xHf_xNb_0.15–yTa_yCoSb Medium-Entropy Alloys: Tradeoff between “What to Alloy” and “How Much to Alloy”

Abstract

Although configurational entropy is regarded to be a gene-like performance indicator for thermoelectric (TE) materials, increasing the configurational entropy alone does not guarantee a high TE figure of merit (ZT). Therefore, determining protocols for designing medium-and high-entropy TE materials with high ZT values is imperative. Herein, we provide a strategy for designing high ZT n-type ZrCoSb-based medium-entropy (ME) half-Heusler (HH) alloys and highlight the tradeoff between "what to alloy" and "how much to alloy". As expected, an intrinsically low lattice thermal conductivity of ∼2.24 W m −1 K −1 was obtained at 923 K for the Zr 0.45 Hf 0.4 Nb 0.06 Ta 0.09 CoSb ME HH alloy owing to the synergy between Zr-site disorder, anharmonicity, refined grain size, and entropy-driven multiscale defects. Entropy-driven quantum traps lead to energy-filter effects that concurrently provide optimized Seebeck coefficients and power factors. These favorable modifications enable the Zr 0.45 Hf 0.4 Nb 0.06 Ta 0.09 CoSb ME HH alloy to exhibit a high peak ZT of ∼0.57. The developed design concept provides an effective strategy for enhancing the ZT values of medium-and high-entropy TE materials.

TaFeSb-Based Half-Heusler Thermoelectrics with High zT > 1 through the Alloying Effect

“…The relatively high thermal conductivity of the HH alloys is widely known, and coalloying is often an effective way to minimize the thermal conductivity. In the following section, in order to enhance the performance of TaFeSb further, Hf/Ti and V/Ti coalloying strategy is employed to reduce the thermal conductivity …”

“…In the following section, in order to enhance the performance of TaFeSb further, Hf/Ti and V/Ti coalloying strategy is employed to reduce the thermal conductivity. 44 3.3. Co-Alloyed TaFeSb.…”

A comprehensive review of entropy engineered GeTe: an antidote to phase transformation

“…This enhances the thermoelectric performance unlike the earlier trend of designing complex crystal structures for reducing the lattice thermal conductivity alone. 87–93…”

“…Although considerable headway has been made with the high entropy materials towards designing novel alloys for thermoelectric applications, in this review our aim is to solve the fundamental problem pertaining to phase transition in GeTe and suppressing it to ambient temperature from 700 K via entropy engineering so that the alloys with superior band structures can be utilized for the fabrication of thermoelectric devices. 87–93…”

Development of Thermoelectric Half-Heusler Alloys over the Past 25 Years

“…(Ti,Zr,Hf,X)NiSn Nb [105] (Ti,Zr,Hf)(Ni,X)Sn Cu [170] (Ti,Zr,Hf,X)NiSn/Z V + Nb Sb [174] (Ti,Zr)Ni 1±x Sn [22,110,171] (Ti,Zr)Ni 1±x Sn [138] (Zr,Hf)Ni 1±x Sn [77] TiNiSn+full Heusler [83] TiNiSn+HfO 2 [149] ZrNiSn+B [29] * ZrNiSn+La [108] ZrNiSn+ZrO 2 [35] ZrNiSn+ZnO [153] (Zr,Hf)NiSn+W [197] (Zr,Hf)NiSn+ZrO 2 [95] ( (Zr,X)CoSb Nb [156] Zr(Co,X)Sb Ni [141] HfCoSb [45,46,56,177,195] (Hf,X)CoSb Nb [182] (Ti,Zr)CoSb [67] (Ti,Zr)(Co,X)Sb Ni [67] (Ti,Hf,X)CoSb Ta [204] (Zr,Hf,X)CoSb Nb [158,182] Nb + Ta [214] (Ti,Zr,Hf)CoSb [56,64] (Ti,Zr,Hf)(Co,X)Sb Ni [64] (V,Nb,Ta)FeSb-System VFeSb [74,91,192] (V,X)FeSb Ti [15] NbFeSb [26,148] Nb(Fe,X)Sb Ir [184] (V,Nb)FeSb [92] (V,Nb)(Fe,X)Sb Co [92] Ti(Fe,X)Sb Ni [200] Ti(Fe,X)Sb/Z Ni Sn [13]…”