Facile p–n control, and magnetic and thermoelectric properties of chromium selenides Cr2+xSe3

Abstract

Cr₂Se₃ crystallizes in a NiAs-type structure and is antiferromagnetic with a Néel temperature of T_N = 43 K (M. Yuzuri, 1973). Here seven samples with nominal composition Cr_2+xSe₃ (x = −0.04, −0.02, 0, 0.04, 0.06, 0.08 and 0.12) were prepared by solid state reaction and spark plasma sintering (SPS). The phase composition was characterised by X-ray diffraction (XRD). The electrical conductivity, Seebeck coefficient, thermal conductivity, and Hall effect measurements of all compounds were performed. Both Seebeck coefficients and Hall coefficients show that Cr_2+xSe₃ are p-type materials when x = −0.04, −0.02, 0 and 0.04, and switch to n-type when x = 0.06, 0.08 and 0.12. An effective magnetic moment μ_eff = 3.85 μ_B per Cr ion in Cr₂Se₃ is obtained by the Curie–Weiss law. We also calculate and compare the band gap values of Cr_2+xSe₃ by various methods, such as the Arrhenius formula, the Goldsmid–Sharp equation and the optical spectrum. Moderate zT values are obtained for p-type Cr_2.04Se₃ and n-type Cr_2.08Se₃ at a relatively low temperature above room temperature. These results indicate the availability of p- and n-type legs in binary transition metal chalcogenides and reveal their potential for wide scale thermoelectric applications.