Abstract
Bi2Te3-based alloys have been intensively used for thermoelectric coolers and generators due to their high Seebeck coefficient S. So far, efforts to improve the S have been made mostly on changing the structures and components. Herein, we demonstrate an anomalous thermoelectricity in strained Bi2Te3 films, i.e., the value of S is obviously changed after reversing the direction of temperature gradient. Further theoretical and experimental analysis shows that it originates from the coupling of thermoelectric and flexoelectric effects caused by a stress gradient. Our finding provides a new avenue to adjust the S of Bi2Te3-based thermoelectric materials through flexoelectric polarization.
Highlights
(0, 0, 15) diffraction intensity decreases after annealing, which implies that the crystalline quality of Bi2Te3 films by hot wall epitaxy (HWE) method is sensitive to the growth conditions
It is noted from the low-magnification scanning electron microscopy (SEM) image that many disoriented crystal grains, one of which is labeled by the red rectangle, are observed, which are responsible for the weak (0, 1, 5) and (1, 0, 10) diffraction peaks in X-ray diffraction (XRD) results
As we know that the crystal structure of Bi2Te3 (D35d (R3m) space group) does not belong to the known 20 piezoelectric crystal classes and there is no external electric field applied in the measurements, the internal polarization in Bi2Te3 films may not be induced by ferroelectricity or piezoelectricity
Summary
(0, 0, 15) diffraction intensity decreases after annealing, which implies that the crystalline quality of Bi2Te3 films by HWE method is sensitive to the growth conditions. Thermoelectricity of strained Bi2Te3 films on InAs and GaAs substrates.
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