The electrical conductivity of the cubic phase, which is larger than that of the monoclinic phase, and similar thermal conductivities of the two phases lead to the higher ZT of the cubic Cu₂SnSe₃.

SnSe is considered as a promising thermoelectric (TE) material since the discovery of the record figure of merit (ZT) of 2.6 at 926 K in single crystal SnSe. It is, however, difficult to use single crystal SnSe for practical applications due to the poor mechanical properties and the difficulty and cost of fabricating a single crystal. It is highly desirable to improve the properties of polycrystalline SnSe whose TE properties are still not near to that of single crystal SnSe. In this study, in order to control the TE properties of polycrystalline SnSe, polycrystalline SnSe–SnTe solid solutions were fabricated, and the effect of the solid solution on the electrical transport and TE properties was investigated. The SnSe_1−xTe_x samples were fabricated using mechanical alloying and spark plasma sintering. X-ray diffraction (XRD) analyses revealed that the solubility limit of Te in SnSe_1−xTe_x is somewhere between x = 0.3 and 0.5. With increasing Te content, the electrical conductivity was increased due to the increase of carrier concentration, while the lattice thermal conductivity was suppressed by the increased amount of phonon scattering. The change of carrier concentration and electrical conductivity is explained using the measured band gap energy and the calculated band structure. The change of thermal conductivity is explained using the change of lattice thermal conductivity from the increased amount of phonon scattering at the point defect sites. A ZT of ~0.78 was obtained at 823 K from SnSe_0.7Te_0.3, which is an ~11% improvement compared to that of SnSe.

A novel synthesis method to prepare Si₃N₄ nanowires from amorphous silicon nitride (a-Si₃N₄) powder synthesized by a low-temperature vapor-phase reaction method was investigated. Highly crystalline α-Si₃N₄ nanowires were synthesized by heat treatment of the a-Si₃N₄ powder under ammonia atmosphere. The surface of the nanowires was smooth and clean without any attached particles. The thickness of the nanowires was in the range of ∼200–300 nm with lengths of tens of micrometers. The nucleation of nanowires from the reaction between SiO and N₂ occurs on the surface of the a-Si₃N₄ powder, which is covered by a thin layer of SiO₂, and the nanowires grow from the rearrangement of Si and N atoms of the a-Si₃N₄ powder. The reduction of SiO₂ to SiO by ammonia was promoted in the presence of a Ni catalyst; therefore, the growth was observed at a lower temperature when Ni was added to the a-Si₃N₄ powder than in the presence of added Fe. The growth of α-Si₃N₄ nanowires occurs along the [100, 101] direction and follows the vapor–solid–solid mechanism.