Thermoelectric Properties of Chromium Selenides

Start your abstract here Magnetic semiconductors, such as CuFeS₂ and Mn-doped CuGaTe₂ with chalcopyrite structure, have received considerable attention due to their excellent thermoelectric properties [1, 2]. This paper reports the preparation and thermoelectric properties of a transition metal chalcogenides, chromium selenide Cr₂Se₃.

The chromium selenide Cr₂Se₃ adopts a rhombohedral structure with space group R3 based on NiAs-type structure. There is Cr vacancy ordering in every second metal layer. Rhombohedral Cr₂Se₃ is reported by Y.Adachi et al. to be antiferromagnetic with Néel temperature T _N = 43 K. [3] It was also found that Cr₂Se₃ is metallic when the temperature is over T _N, deducing from the temperature dependence of electrical resistivity. K.R.Pisharody prepared chromium sulfo-selenides Cr2S_3-xSe_x (0 ≤ × ≤ 1) by reacting high purity in quartz tubes at 1273 K. All the samples are n-type materials showing negative Seebeck coefficient values and zT = 0.1 was achieved in Cr₂Se₃ at 500 K.

In this work, we have prepared Cr_2+xSe₃ (-0.04 ≤ × ≤ 0.08) by reacting the elements and investigated the effect of Cr content on thermoelectric properties. All the samples are indexed to be the Cr₂Se₃ phase, as observed from the powder X-ray diffraction (XRD) pattern. According to the onset temperature (T _max) of the intrinsic conduction and the Seebeck coefficient αmax at Tmax, The band gap values 0.22 eV for Cr_2.04Se₃ and 0.17 eV for Cr_2.08Se₃ were estimated using the equation E _g = 2α _max T _max,[4] where T _max is the onset temperature of the intrinsic conduction and αmax the Seebeck coefficient peak αmax at T _max. The change in the conduction type from p-type to n-type was observed when the amount of Cr is over 2.04. For all the samples, the thermal conductivity increases with the increasing temperature. The highest zT = 0.22 was gained in p-type Cr_2.04Se₃ and zT = 0.12 for n-type Cr_2.08Se₃. Magnetic properties or Hall effect measurement remains to be performed. (paper)