Effect of Sm-doping on microstructure and thermoelectric properties of textured n-type Bi2Te2.7Se0.3 compound due to change in ionic bonding fraction

Textured n-type Bi2-xSmxTe2.7Se0.3 compounds with x = 0; 0.005; 0.02 and 0.05 have been prepared by microwave-solvothermal synthesis of starting powders and spark plasma sintering of bulk materials. Texturing [001] axis coincided with direction of spark plasma sintering pressuring. With increasing x, (i) an average lateral size of grains in the samples is decreasing; (ii) the Lotgering factor characterizing a degree of preferential orientation of the grains is increasing; (iii) anomalies of all the thermoelectric properties, related to onset of intrinsic conductivity, are shifted to higher temperatures. The Sm-doping effect on the grain structure and thermoelectric properties of samples is attributed to increasing in ionic bonding fraction, which can occur at increasing Sm content due to a difference in electronegativity of Bi and Sm atoms. Maxima in temperature dependences of the thermoelectric figure-of-merit, typical for Bi2Te3-based compounds and due to the intrinsic conductivity, were observed. The highest value of the thermoelectric figure-of-merit was found to be weakly dependent on x and falling into similar to 0.6 divided by similar to 0.7 interval, whereas temperature position of the maxima is remarkably shifted to higher temperatures with increasing Sm content.

Automated summary

Textured n-type Bi2-xSmxTe2.7Se0.3 compounds were prepared with different Sm doping levels, and increasing Sm content led to smaller grain size, higher grain orientation, and a shift of thermoelectric anomalies related to intrinsic conductivity to higher temperatures. Additionally, the thermoelectric figure-of-merit peak temperature increased with higher Sm content while the value remained relatively constant in the range of 0.6 to 0.7.