Current Happenings

Projects: Oxides



Researches on Na1-xMgxV2O5

The phase transition of needle-like single crystalline specimens of NaV2O5 at 33K is a complicated cooperative process. After Mg doping, we observed Na1-xMgxV2O5 (nominally, x=0.00-0.35) had a pronounced thermal conductivity dip and a specific heat anomaly at T, where the phase transition occurs. A close relation has been established among the Na/Mg concentration, transition temperature T, the position and amplitude of the thermal conductivity dip and specific heat anomaly. The underlying mechanisms have been discussed in light of the disorder nature of this low-dimensional compound.

Researches on Bi2Te3

Hydrothermal treatment of polycrystalline p-Bi2Te3 by alkali metal salt ABH4 (A= Na or Rb) solution resulted in lower thermal conductivity for Na-treatment and higher power factor for Rb-treatment owing to a thin layer formed at the grain boundary. By combining both Na- and Rb-treatment with various molar ratios, a similar grain boundary layer is formed with a compositional gradient along the depth direction. Hall effect measurements showed that the grain boundary phase introduced new carriers into the system and thereby compensated the loss in mobility. With the Seebeck coefficient largely retained, the electrical conductivity to thermal conductivity ratio has been optimized by varying the Na:Rb ratio in the starting solution. As a result, the Na:Rb ~ 1:2 ratio yields the best dimensionless figure of merit ZT value ~ 0.92 at 350K, comparable with that of the start-of-the art p-Bi2Te3 commercial ingot.



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