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By using the solid-state reaction approach, composite polycrystalline samples of (Bi0.98In0.02)2Te2.7Se0.3/x%Bi2Se3 were created with varying amounts of Bi2Se3, (x = 5%, 10%, 15%, and 20%). The hexagonal crystal structure of the composite was revealed by x-ray diffraction (XRD) with a space group of R$$\overline{3 }$$ 3 ¯ m. The surface of the samples was seen to have secondary particles using a field emission scanning electronic microscope. Every sample displayed the typical semi-conducting behaviour across the entire temperature range. In the complex (Bi0.98In0.02)2Te2.7Se0.3, it was found that bismuth was coordinated with six selenium atoms and there were significant selenium vacancies. With an increase in bismuth selenide concentration, the dissolution pattern shifted to a substitutional pattern. A two fold decrease in electrical resistivity for (Bi0.98In0.02)2Te2.7Se0.3/20%Bi2Se3 composition was seen compared to (Bi0.98In0.02)2Te2.7Se0.3/5%Bi2Se3. The granular material was produced by sintering and scattering of potential barrier, a thermal process that increases the Seebeck coefficient. A 200% increase was observed in thermopower for (Bi0.98In0.02)2Te2.7Se0.3/20%Bi2Se3 compared to (Bi0.98In0.02)2Te2.7Se0.3/5%Bi2Se3 compound. Graphical Abstract

Polycrystalline composite samples of (Bi0.98In0.02)2Se2.7Te0.3/Bi2Te3 with different concentrations of Bi2Te3 such as 5%,10%,15% and 20% were prepared by the solid-state reaction technique. The X-Ray diffraction analysis has shown the hexagonal composite crystal structure with space group of $$R\overline{3 }$$ R 3 ¯ m. Field emission scanning electronic microscope shows secondary particles on the surface of the samples. All the samples have shown the usual semi-conducting behaviour throughout the temperature range. It is observed that bismuth has been co-ordinated with 6 selenium atoms in (Bi0.98In0,02)2Se2.7Te0.3 compound and it has enormous selenium vacancies. The electrical resistivity represents the noteworthy result of the grain boundaries leading to the higher content of scattering centres in the polycrystalline composite samples. It is found that the electronegativity differences of In and Te, In and Se are less than Bi and Se, Bi and Te is the reason for the decrease in Seebeck coefficient in the compound containing 15% and 20% of Bi2Te3.

We present report on modulating thermoelectric transport in Cu2SnSe3system via irradiating high-energy electrons of energy of about 8 MeV. Electrical transport is investigated at near room to mid-temperature regime (300–700 K). A smooth transition from degenerate to non-degenerate type of conductivity is observed in all the samples, which indicates the injection of minority carriers with ionisation of defects at high temperatures. Defects created through the knock-on displacement of the constituent atoms is successful in promoting the power factor in the material. Cu2SnSe3irradiated with 50 kGy is found to achieve highest power factor of 228 µW/mK2at 700 K, which is nearly 20% higher than the power factor of pristine material at the same temperature.

We herein report on compositing highly conductive GdH2 with BiCuSeO, with an aim to modulate the electronic transport and the nature of conductivity in the high-temperature regime. The incorporation of GdH2 as a minor matrix in BiCuSeO, as confirmed by structural studies, has considerably enhanced electrical conductivity in the system, thereby demonstrating the existence of thermal activation of the charge carriers. The effect of minor matrix is directly on the conversion of p-type to n-type conductivity in BiCuSeO system at near room temperature. Electronic quality factor (BE) has identified the ambiguities in the transport behaviour at near room temperature due to the addition of minor matrix. Enhancement in the power factor is seen due to GdH2, with a highest attained value of 221 μW m K−2 at 700 K for the sample with x = 11 wt%, which is nearly twice the value of pristine BiCuSeO. Highest ZT of 0.011 is obtained for the pristine BiCuSeO sample at 380 K.

The modification in the Cu2Se thermoelectric system by electron beam irradiation has been carried out in this work. Samples were prepared using the solid-state reaction technique. The prepared samples were irradiated with various energy dosages viz. 50, 100, and 150 kGy. XRD studies reveal that the synthesized samples crystallized in a monoclinic structure. The micro-hardness of the samples decreased with an increase in irradiation dosage. The sample irradiated at 100 kGy dose exhibits the lowest electrical resistivity, moderate Seebeck coefficient, and highest power factor.

A detailed investigation on the temperature dependent electrical properties of Cu2SnSe3 system, synthesized via conventional solid-state reaction at different sintering temperatures are presented in this communication. All the samples exhibit degenerate semiconducting nature at low temperatures. The existence of small polarons and hence electron–phonon interactions are confirmed at temperatures below 400 K. A transition was observed from degenerate to non-degenerate semiconducting behaviour at high temperatures (T > 400 K). The study confirms the unusual transition in electrical resistivity as well as thermopower at high temperatures in all the compounds, demonstrating the existence of minority carrier excitation along with temperature-triggered ionisation of the defects. The transport behaviour is further supported by an upward movement of Fermi level away from the valence band. Highest weighted mobility of 8.2 cm2 V−1 s−1 at 673 K was obtained for the sample sintered at 1073 K. A considerable decrease in electrical resistivity with increase in temperature (T > 400 K) has driven the power factor to increase exponentially, thereby achieving highest value of 188 µV/mK2 (at 673 K) for the sample sintered at 673 K. Graphic abstract

The substitution of Cu by Mn in the Cu2-xMnxSnSe3 (0 ≤ x ≤ 0.20) system is presented with an objective to optimize the thermal transport and analyse thermoelectric behaviour in the low and near room temperature regime (10–350 K). The existence of hole-like small polarons as thermally activated carriers, mediating the p-type electrical transport at high temperatures (>80 K), is experimentally validated. Temperature dependence of Seebeck coefficient and electrical transport at low temperatures reveals that the variable range hopping (VRH) mechanism is responsible for conduction for temperatures (

To investigate the thermoelectric properties, we have attempted to tune selenium content in Cu2SnSe3-δ (−0.04 ≤ δ ≤ 0.1) compounds synthesized via the conventional solid-state reaction. Electrical and thermal properties are presented in the low and near room temperature regime (10–350 K). The lowest electrical resistivity is observed for the compound with δ = 0.08. The electron-phonon coupling and the presence of small polarons are experimentally validated from temperature-dependent electrical and thermal transport data. A decrease in the Seebeck coefficient along with carrier concentration is observed, verifying the linear electron band dispersion. A downward shift of the Fermi level deep into the valence band is realized in the case of non-stoichiometric samples, thereby reducing the Seebeck coefficient. A maximum power factor of ~50 μWmK−2 is achieved for the sample with δ = 0.04, which is about twice that of the pristine compound. The highest ZT of ~0.01 is obtained for the compound with δ = 0.08. The observed results suggest that stoichiometry plays a vital role in tuning the thermoelectric properties in the Cu2SnSe3 compound.