High-Power Factor Enabled by Efficient Manipulation Interaxial Angle for Enhancing Thermoelectrics of GeTe-Cu₂Te Alloys

Abstract

The emerged strategy of manipulating the rhombohedral crystal structure provides another new degree of freedom for optimizing the thermoelectric properties of GeTe-based compounds. However, the concept is difficult to be effectively measured and often depends on heavy doping that scatters carriers severely. Herein, we synergistically manipulate lattice distortion and vacancy concentration to promote the excellent electrical transport of GeTe-Cu2Te alloys and quantify the interaxial angle-dependent density of state effective mass. Distinct from the conventional electronic coupling effect, about 2% substitution of Zr4+ significantly increases the interaxial angle, thereby enhancing the band convergence effect and improving the Seebeck coefficient. In addition, Ge-compensation attenuates the mobility deterioration, leading to improved power factor over the whole temperature range, especially exceeding ∼22 μW cm–1 K–2 at 300 K. Furthermore, the Debye–Callaway model elucidates low lattice thermal conductivity due to strong phonon scattering from Zr/Ge substitutional defects. As a result, the highest figure of merit zT of ∼1.6 (at 650 K) and average zT ave of ∼0.9 (300–750 K) are obtained in (Ge1.01Zr0.02Te)0.985(Cu2Te)0.015. This work demonstrates the effective band modulation of Zr on GeTe-based materials, indicating that the modification of the interaxial angle is a deep pathway to improve thermoelectrics.

High Thermoelectric Performance of Non‐Stoichiometric and Oriented GeTe Thin Films

“…The changing value of the interaxial angles is large enough to indicate that the crystal structure symmetry of rhombohedral GeTe films has been enhanced. [38,39] It can be further confirmed in the temperature-dependent XRD results. When the temperature increases from 323 K to 623 K, the (003) and (021) peaks finally merge to one (111) peak (Figure 2c), cor-responding to the phase transition from the rhombohedral phase into the cubic phase of GeTe.…”

Electrical Property Enhancement in Orientation‐Modulated Perovskite La‐Doped SrTiO3 Thermoelectric Thin Films

“…Due to the high-temperature endurance, chemical stability, non-toxicity, and abundance in earth, oxides are irreplaceable as thermoelectrics. [13][14][15][16][17] In n-type thermoelectrics, there were researches on ZnO, [18][19][20][21][22][23] CdO, [24] TiO 2 , [25,26] In 2 O 3 [27][28][29] -based simple oxides, and Bi 2 O 2 Se, [30,31] Bi 2 LnO 4 Cu 2 Se 2 , [32] Sr 2 MO 2 Cu 2 Se 2 (M = Co, Ni, Zn) [33] -based layered oxides, while the simple crystal structure providing few elemental sites to be tuned, and low symmetry of layered oxides resulting in low electron effective mass, [34][35][36][37][38] limited the enhancement of their electrical properties. Strontium Titanate (SrTiO 3 ) as a cubic phase perovskite oxide possesses high symmetry and high density of states near the conduction band minimum (CBM), thus having a relatively large density of states effective mass and outperforming power factors.…”

Two-step phase manipulation by tailoring chemical bonds results in high-performance GeSe thermoelectrics

“… 25 Recently, a slight symmetry-breaking strategy in rhombohedral GeTe has been employed to manipulate the interaxial angle ( θ ) and the atomic-site displacement ( Δ ), triggering the convergence of multivalence bands for high TE performance. 26 , 27 , 28 , 29 …”