Synthesis, electronic structure and physical properties of polycrystalline Ba2FePnSe5 (Pn = Sb, Bi)

Abstract

We report a new synthesis route towards polycrystalline Ba2FePnSe5 (Pn = Sb, Bi) chalcogenides based on ball milling and subsequent spark plasma sintering. The polycrystalline samples were characterized by transmission electron microscopy and powder X-ray diffraction. We discovered that both compounds undergo rapid, radiation induced phase changes between a crystalline and an amorphous phase. Thin layers of amorphous Ba2FePnSe5 (Pn = Sb, Bi) were obtained by applying 0.3 ms laser pulses (λ = 1064 nm) on the surface of polycrystalline samples. By using a series of subsequent laser pulses at room temperature the surface of Ba2FeBiSe5 can be reversibly changed between amorphous and crystalline states. The thermal conductivity can be used to follow the amorphization and recrystallization processes as a function of laser pulses. Resistivity measurements and calculations of the electronic structure revealed band gaps of 1.04 eV (Pn = Bi) and 1.14 eV (Pn = Sb). We found anomalies in the thermal conductivity of Ba2FePnSe5 (Pn = Sb, Bi) at the Neel temperature due to the antiferromagnetic ordering of the Fe spins. We also show that the distortion of the PnSe6 octahedra is caused by stereoactive 5s2 and 6s2 lone pairs of Sb and Bi.