Hong-Quan Liu

A simple synthesis and characterization of PbTe nano-particles

PbTe nanopowders with different morphology were prepared by a simple chemical synthesis. Similar cubic nanoparticles have been successfully synthesized by using Pb(NO3)2 and Na2TeO3 as the precursors, and NaBH4 as the reductant. The single PbTe phase is confirmed from XRD pattern, and obvious width of XRD peaks occur. The size of powders is distributed from 20nm to 70nm in a typical process according to observation from SEM and TEM images. Based on HRTEM observation, PbTe nanopowders with an amorphous layer show polyhedron feature. In different crystallization stages, there is different morphology due to competition between surface energy and crystal face energy. The globular, polyhedron and cubic particles belongs to different growth stages, respectively. Possible growth mechanisms of PbTe were also discussed.

Enhanced thermoelectric properties of Co1-x-yNix＋ySb3-xSnx materials

Co1−x−yNix+ySb3−xSnx polycrystals were fabricated by vacuum melting combined with hot-press sintering. The effect of alloying on the thermoelectric properties of unfilled skutterudite Co1−xNixSb3−xSnx was investigated. A leap of electrical conductivity from the Co0.93Ni0.07Sb2.93Sn0.07 sample to the Co0.88Ni0.12Sb2.88Sn0.12 sample occurs during the measurement of electrical conductivity, indicating the adjustment of band structure by proper alloying. The results show that alloying enhances the power factor of the materials. On the basis of alloying, the thermoelectric properties of Co0.88Ni0.12Sb2.88Sn0.12 are improved by Ni-doping. The thermal conductivities of Ni-doping samples have no reduction, but their power factors have obvious enhancement. The power factor of Co0.81Ni0.19Sb2.88Sn0.12 reaches 3.0 mW·m−1·K−2 by Ni doping. The dimensionless thermoelectric figure of merit reaches 0.55 at 773 K for the unfilled Co0.81Ni0.19 Sb2.88Sn0.12.

Mixed Mn3+/Mn4+ in high-voltage nano-structured lithium nickel manganese oxide cathode with a P4332 structure

In this paper, we have synthesized LiNi0.5Mn1.5O4 with P4332 space group by carbonate co-precipitation. TG/DSC, TG*, ICP-OES, a gas displacement pycnometer using He gas, XPS, and XRD refinement results show that oxygen vacancies exist in the LiNi0.5Mn1.5O4−δ with a P4332 space group. There is a mixture of Mn3+ and Mn4+ in the P4332 structured LiNi0.5Mn1.5O4−δ. Despite the large amount of Mn3+ in the spinel structure, no 4.0V plateau appears in charge–discharge curves. This result indicates that the Mn3+ in LiNi0.5Mn1.5O4−δ does not participate in electrochemical reactions during the charge–discharge process.