Zintl-phase Eu ₂ ZnSb ₂ : A promising thermoelectric material with ultralow thermal conductivity

Abstract

Zintl compounds are considered to be potential thermoelectric materials due to their “phonon glass electron crystal” (PGEC) structure. A promising Zintl-phase thermoelectric material, 2-1-2–type Eu2ZnSb2 (P63/mmc), was prepared and investigated. The extremely low lattice thermal conductivity is attributed to the external Eu atomic layers inserted in the [Zn2Sb2]2- network in the structure of 1-2-2–type EuZn2Sb2(P3¯m1), as well as the abundant inversion domain boundary. By regulating the Zn deficiency, the electrical properties are significantly enhanced, and the maximum ZT value reaches ∼1.0 at 823 K for Eu2Zn0.98Sb2. Our discovery provides a class of Zintl thermoelectric materials applicable in the medium-temperature range.

Vacancy ordering induced topological electronic transition in bulk Eu 2 ZnSb 2

“…5A ) and zigzag-stagger (Z-stagger, Fig. 5B ) structures have space group symmetry Pmm 2 ( 25 ), which is noncentrosymmetric due to lack of mirror symmetry in the z direction. We find only very small changes in the lattice parameter after full structural relaxation of the models, consistent with the experiment.…”

“…These included CaCuSb (21), LiZnSb (22), and AZn 2 Sb 2 (A = Ca, Sr, Eu, and Yb) (23). There is also a recently found compound Eu 2 ZnSb 2 , which is reported to have a hexagonal structure (24) and can be modified to yield a high-performance TE material, with a respectable TE figure of merit ZT = 1 (25). Because of the Zintl electron counting rules, the compound has a stoichiometry that leaves half of the Zn sites in the honeycomb lattice empty.…”

“…The original crystal structure is maintained rather than forming reconstructed geometries as in Ba 2 ZnSb 2 (31). From the point of view of TE performance, it is important to note that the structural complexity due to the large numbers of vacancies on the honeycomb sheets could efficiently scatter phonons, reducing the thermal conductivity and thus favoring high ZT values (25,(32)(33)(34). Moreover, the partially filled Zn sublattice can introduce additional complexity, since the Zn vacancies may not be fully random.…”

New n-Type Zintl Phases for Thermoelectrics: Discovery, Structural Characterization, and Band Engineering of the Compounds A2CdP2 (A = Sr, Ba, Eu)

“…To this end, Zintl phases with a layered structure have garnered attention from the thermoelectric community: the "1-2-2" family (e.g., EuZn 2 Sb 2 10 ) and "1-1-1" family (e.g., KSnSb 11 ) to name just a few. The "1-2-2" family [12][13][14] of layered Zintl 15 another new material with a layered structure, have shown moderate zT due to improved Seebeck coefficient in combination with the features inherited from the "parent" Yb 2 CdSb 2 structure. 16 The herein discussed newly synthesized phases, A 2 CdP 2 (A = Sr, Ba, Eu), also belong to the same layered structure type with space group Cmc2 1 , and their thermoelectric assessment using computational methodology, specifically the quality factor, 17 shows very promising n-type metrics.…”

New n-type Zintl Phases for Thermoelectrics: Discovery, Structural Characterization and Band Engineering of the Compounds A2CdP2 (A = Sr, Ba, Eu)

“…To this end, Zintl phases with a layered structure have garnered attention from the thermoelectric community: the "1-2-2" family (e.g., EuZn 2 Sb 2 10 ) and "1-1-1" family (e.g., KSnSb 11 ) to name just a few. The "1-2-2" family [12][13][14] of layered Zintl phases in the CaAl 2 Si 2 structure type, for example, exhibit low lattice thermal conductivities and high Seebeck coefficient, leading to highly competitive zT values (e.g. zT = 1.2 at 700 K for the system EuZn 1.8 Cd 0.2 Sb 2 10 ).…”