Publication
Converting Brownmillerite to Alternate Layers of Oxygen‐Deficient and Conductive Nano‐Sheets with Enhanced Thermoelectric Properties
Publisher:
Wiley
Date:
11-06-2022
DOI:
10.1002/AENM.202201469
Abstract: Introducing large oxygen deficiencies while retaining low resistivity is important for enhancing the overall thermoelectric properties in 3d transition‐metal oxides. In this study, a new synthesis route to reconstruct the insulating brownmillerite SrCoO 2.5 is adapted. Through a step‐by‐step nano‐blocks modification, a series of highly‐conductive layered structures is evolved, which are [Sr 2 O 2 H 2 ] 0.5 CoO 2 , [Sr 2 O 2 ] 0.4 CoO 2 , and [Sr 2 CoO 3 ] 0.57 CoO 2 , while still retaining considerable Seebeck coefficient ( ≈ 100 µ V K −1 ). Coexistence of low resistivity and high oxygen deficiency is realized in the latter two polymorphs by forming a majority of sintered oxygen vacancies in the rock‐salt layer and a minority of normal oxygen vacancies in the CoO 2 layer. A room‐temperature in‐plane power factor of 3.6 mW K −2 m −1 , power output density of 4.5 W m −2 at a temperature difference of 28 K, and an out‐of‐plane thermal conductivity of 0.33 W K −1 m −1 are obtained in the [Sr 2 O 2 ] 0.4 CoO 2 thin film that exhibits the highest oxygen deficiency (δ = 2.95), which is on par with Bi 2 Te 3 , the benchmark. It is pointed out that proper distribution of oxygen vacancy is essential in tailoring the physical and chemical properties of transition‐metal oxides. The sintered/normal oxygen vacancy layer model provides guidance to the exploration of materials with both low electric resistivity and thermal conductivity.