Abstract

Herein, we present the solid-state synthesis, structural, thermoelectric, and magnetoresistance characterization of Cu[Cr2-xMx]Se-4 selenospinels (x = 0.3 and 0.5; M = Sn, Ti). Powder X-ray diffraction patterns were fitted using the Rietveld method and are consistent with a spinel-type structure ( F(-)d3m space group) and corroborated by Raman spectroscopy and single-crystal X-ray diffraction. The microstructures and morphologies of these systems were examined using high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The transport properties of all compounds exhibit a decreasing electrical conductivity (20-600 K) and an increasing Seebeck coefficient (300-600 K) as a function of temperature, displaying typical metallic behavior associated with electron scattering by thermal vibrations of the crystal lattice (electron-phonon scattering), which is corroborated by DFT calculations. We determined that the Seebeck coefficient increases from approximately +21 mu V K-1 (250 K) to +43 mu V K-1 (550 K) in CuCr1.5Sn0.5Se4. Additionally, the selenospinels exhibit electrical conductivities (sigma) of similar to 1000-2000 S cm(-1) at 250 K, comparable to that of the CuCr1.2Ti0.8S4 thiospinel. The carrier concentrations (Hall measurements) and Seebeck coefficients are positive, indicating p-type behavior with a hole concentration of similar to 10(19) cm(-3) for all samples at room temperature. Changes in slope are observed for both Sn and Ti selenospinels, indicating two distinct conduction regimes. The thermal conductivity (kappa(tot)) is similar to 3.0 W m(-1) K-1 for Cu[Cr1.7Ti0.3]Se-4 and Cu[Cr2-xSnx]Se-4 samples at room temperature. The lattice thermal conductivity (kappa(latt)) exhibits remarkably low values (similar to 1.5 W K-1 m(-1)) for Cu[Cr2-xSnx]Se-4, reaching levels comparable to those of established high-performance thermoelectric materials, and is lower than those reported for CuTi2S4 spinel at 300 K (similar to 2.5 W K-1 m(-1)). The magnetoresistance reaches a maximum of similar to 40% close to the ferromagnetic/paramagnetic phase transition temperature.