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

The emerged strategy of manipulating the rhombohedral crystal structure provides another new degree of freedom for optimizing the thermo-electric 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 mu W 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 zTaveof -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.

Automated summary

By synergistically manipulating lattice distortion and vacancy concentration, excellent electrical transport properties of GeTe-Cu2Te alloys were promoted, and the interaxial angle-dependent density of state effective mass was quantified. The effective band modulation of Zr on GeTe-based materials was demonstrated, enhancing the band convergence effect and improving the Seebeck coefficient. Ge-compensation attenuated the mobility deterioration, leading to improved power factor, and low lattice thermal conductivity was achieved due to strong phonon scattering from Zr/Ge substitutional defects. The highest figure of merit zT of -1.6 (at 650 K) and average zTave of -0.9 (300-750 K) were obtained in (Ge1.01Zr0.02Te)0.985(Cu2Te)0.015 alloy.