Solid-state synthesis, structural characterization, and transport properties of cubic ferromagnetic Cu[Cr2-xMx]Se4 selenospinels

Abstract:

Herein, we present the solid-state synthesis, structural, thermoelectric, and magnetoresistance characterization of Cu[Cr<inf>2-x</inf>M<inf>x</inf>]Se<inf>4</inf> 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 (Fd3‾m 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 μV K⁻¹ (250 K) to +43 μV K⁻¹ (550 K) in CuCr<inf>1.5</inf>Sn<inf>0.5</inf>Se<inf>4</inf>. Additionally, the selenospinels exhibit electrical conductivities (σ) of ∼1000-2000 S cm⁻¹ at 250 K, comparable to that of the CuCr<inf>1.2</inf>Ti<inf>0.8</inf>S<inf>4</inf> thiospinel. The carrier concentrations (Hall measurements) and Seebeck coefficients are positive, indicating p-type behavior with a hole concentration of ∼10¹⁹ 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 (κ<inf>tot</inf>) is ∼3.0 W m⁻¹ K⁻¹ for Cu[Cr<inf>1.7</inf>Ti<inf>0.3</inf>]Se<inf>4</inf> and Cu[Cr<inf>2-x</inf>Sn<inf>x</inf>]Se<inf>4</inf> samples at room temperature. The lattice thermal conductivity (κ<inf>latt</inf>) exhibits remarkably low values (∼1.5 W K⁻¹ m⁻¹) for Cu[Cr<inf>2-x</inf>Sn<inf>x</inf>]Se<inf>4</inf>, reaching levels comparable to those of established high-performance thermoelectric materials, and is lower than those reported for CuTi<inf>2</inf>S<inf>4</inf> spinel at 300 K (∼2.5 W K⁻¹ m⁻¹). The magnetoresistance reaches a maximum of ∼40% close to the ferromagnetic/paramagnetic phase transition temperature.

Año de publicación:

2026

Keywords:

• Half-metallic ferromagnets
• Magnetoresistance behavior
• Selenospinels
• Thermoelectric properties

Fuente:

scopus