Exploring Tantalum as a Potential Dopant to Promote the Thermoelectric Performance of Zinc Oxide.

Arias-Serrano Arias-Serrano,Weidenkaff Weidenkaff,Xie Xie,Frade Frade,Mikhalev Mikhalev,Kovalevsky Kovalevsky,Tobaldi Tobaldi,Rasekh Rasekh,Sarabando Sarabando,Aguirre Aguirre

doi:10.3390/ma12132057

Abstract

Zinc oxide (ZnO) has being recognised as a potentially interesting thermoelectric material, allowing flexible tuning of the electrical properties by donor doping. This work focuses on the assessment of tantalum doping effects on the relevant structural, microstructural, optical and thermoelectric properties of ZnO. Processing of the samples with a nominal composition Zn1−xTaxO by conventional solid-state route results in limited solubility of Ta in the wurtzite structure. Electronic doping is accompanied by the formation of other defects and dislocations as a compensation mechanism and simultaneous segregation of ZnTa2O6 at the grain boundaries. Highly defective structure and partial blocking of the grain boundaries suppress the electrical transport, while the evolution of Seebeck coefficient and band gap suggest that the charge carrier concentration continuously increases from x = 0 to 0.008. Thermal conductivity is almost not affected by the tantalum content. The highest ZT~0.07 at 1175 K observed for Zn0.998Ta0.002O is mainly provided by high Seebeck coefficient (−464 μV/K) along with a moderate electrical conductivity of ~13 S/cm. The results suggest that tantalum may represent a suitable dopant for thermoelectric zinc oxide, but this requires the application of specific processing methods and compositional design to enhance the solubility of Ta in wurtzite lattice.

Highlights

Design and development of thermoelectrics for high-temperature applications imposes several essential requirements on the material properties, with emphasis on high resistance against oxidation and thermodynamic stability under operation conditions
All the observed reflections can be indexed in a hexagonal wurtzite structure, space group (SG) P63 mc (Figure 1C), typical for Zinc oxide (ZnO)-based ceramics processed under the described conditions
In order to assess tantalum as a dopant to promote thermoelectric properties in zinc oxide, a series of the Zn1-x Tax O (x = 0–0.008) samples was prepared by conventional solid-state route from oxide precursors, followed by sintering at 1773 K for 10 h in air

Summary

Introduction

Design and development of thermoelectrics for high-temperature applications imposes several essential requirements on the material properties, with emphasis on high resistance against oxidation and thermodynamic stability under operation conditions. As compared to the traditional low-temperature thermoelectrics [1,2,3,4], oxides represent an appropriate family of materials and offer additional advantages such as relatively low toxicity and high natural abundance of the constituent elements [5]. Zinc oxide (ZnO) is an abundant wide band gap semiconductor possessing a variety of promising catalytic, optoelectronic and photochemical properties [6]. It was considered as a potential thermoelectric material for high-temperature heat-to-electricity conversion [7,8], mainly. Donor doping in zinc oxides can be achieved using elements with the oxidation state 3+ and appropriate coordination preferences to fit the ZnO wurtzite lattice. A promising strategy includes co-doping with various cations, in some cases leading to synergistically enhanced performance due to combined effects on the solubility in wurtzite lattice and microstructural evolution [14,15,16,17,18]

Methods

Results

Conclusion