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We report the enhanced p-type conduction properties in BiCuOSe by doping of monovalent ions (K+). As compared with undoped BiCuOSe, simultaneous increase in both the carrier concentration and the Hall mobility was achieved in the K-doped BiCuOSe. The origin of the enhancement was discussed in terms of the two-band structure in the valence band of the BiCuOSe, and the density of state effective masses of the heavy (∼1.1 me) and light hole (∼0.18 me) were estimated by using Pisarenko relation.

A simple method for the preparation of hollow rock-salt TiO 1Àx N x nanoparticles and their visible-light photocatalytic activities are presented. By thermal annealing of TiO 2 nanoparticles under NH 3 /N 2 gas flow at 800 C, a rock-salt TiO phase was achieved far below its transition temperature to a monoclinic TiO phase (1250 C). The composition of the nanoparticles was revealed to be Ti 0.7 (O 0.67 N 0.33 ) 1 by detailed structural and compositional characterizations, and their structural stability was critically determined by the formation of vacancies and the incorporation of N. The hollow rock-salt TiO 1Àx N x nanoparticles presented efficient visible-light photocatalytic activity, and their origins were discussed.

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The effects of Cu addition on band gap energy, effective mass, and charge transport properties in n-type CuxBi2Te3 composites are presented.

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Abstract:In order to realize high-performance thermoelectric materials, a way to obtain small grain size is necessary for intensification of the phonon scattering. Here, we use a melt-spinning-spark plasma sintering process for making p-type Bi 0.36 Sb 1.64 Te 3 thermoelectric materials and evaluate the relation between the process conditions and thermoelectric performance. We vary the Cu wheel rotation speed from 1000 rpm (~13 ms −1 ) to 4000 rpm (~52 ms −1 ) during the melt spinning process to change the cooling rate, allowing us to control the characteristic size of nanostructure in melt-spun Bi 0.36 Sb 1.64 Te 3 ribbons. The higher wheel rotation speed decreases the size of nanostructure, but the grain sizes of sintered pellets are inversely proportional to the nanostructure size after the same sintering condition. As a result, the ZT values of the bulks fabricated from 1000-3000 rpm melt-spun ribbons are comparable each other, while the ZT value of the bulk from the 4000 rpm melt-spun ribbons is rather lower due to reduction of grain boundary phonon scattering. In this work, we can conclude that the smaller nanostructure in the melt spinning process does not always guarantee high-performance thermoelectric bulks, and an adequate following sintering process must be included.