The efficiency of thermoelectric energy converters is limited by the material thermoelectric figure of merit (zT). The recent advances in zT based on nanostructures limiting the phonon heat ...conduction is nearing a fundamental limit: The thermal conductivity cannot be reduced below the amorphous limit. We explored enhancing the Seebeck coefficient through a distortion of the electronic density of states and report a successful implementation through the use of the thallium impurity levels in lead telluride (PbTe). Such band structure engineering results in a doubling of zT in p-type PbTe to above 1.5 at 773 kelvin. Use of this new physical principle in conjunction with nanostructuring to lower the thermal conductivity could further enhance zT and enable more widespread use of thermoelectric systems.
CuGaTe2 with a chalcopyrite structure demonstrates promising thermoelectric properties. The maximum figure of merit ZT is 1.4 at 950 K. CuGaTe2 and related chalcopyrites are a new class of ...high‐efficiency bulk thermoelectric material for high‐temperature applications.
An in vivo micrografting method was developed to obtain Passiflora latent virus (PLV)-free passion fruit from infected plants. The scion length required to eliminate PLV was ≤ 2 mm. The method ...required no aseptic handling and the procedure was relatively simple, and resulted in more than 10 micrografts in one hour. Moreover, no special equipment or procedures were necessary, allowing it to be conducted at an individual farm level. Rapid growth of the scion after grafting was also observed due to the use of fully established seedlings as rootstock. Leaf samples for analysis of PLV infection could therefore be obtained about two months after grafting with fruit harvest possible about four months later. In vivo micrografting was conducted with a scion length of 0.5–1 mm from September to November to determine the optimal air temperature conditions. The graft success rate increased from 18% to 58% with a decrease in the average air temperature from September (28.6°C) to November (23.3°C), although there was no significant difference in PLV-free rates between months (73% to 80%). Accordingly, in vivo micrografting of passion fruit is not recommended under high air temperature conditions. The effect of scion shoot storage conditions was also examined, revealing that in vivo micrografting using shoots stored for one day could be performed without difficulty, whereas the rate of graft success and PLV-free rate were close to those obtained using shoots selected less than 30 min before. These findings suggest that with this method, virus-free plants can be obtained using PLV-infected shoots selected in the field one day earlier. In conclusion, our in vivo micrografting technique is useful to eliminate PLV from infected plants; it is simple and leads to rapid growth of the scion after grafting.
Thermoelectric (TE) generators can directly generate electrical power from waste heat and are promising for use in power supplies and for realizing sustainable energy management. However, the low ...efficiencies of TE materials in converting heat to electricity is the main impediment to applying TE generators in many industries including exhaust heat recovery in automobiles. The efficiency of TE materials is quantified by a dimensionless figure of merit ZT. To enhance ZT, it is important to reduce the lattice thermal conductivity (κlat) of a material while maintaining a high electrical conductivity. Here, we review the TE properties of thallium‐based compounds, mainly tellurides. Many thallium tellurides exhibit extremely low κlat below 0.5 W m−1 K−1, which is almost one third that of Bi2Te3 used in current TE devices. Of the thallium tellurides, Ag9TlTe5 has the highest ZT value of 1.2, which is higher than typical ZT values 0.8 of Bi2Te3; this is primarily due to the extremely low κlat of Ag9TlTe5. In addition, we briefly review the TE properties of tellurides of other group 13 elements that contain structural vacancies such as Ga2Te3. Tellurides exhibit various vacancy distributions and hence have interesting TE properties. Based on the results of the TE properties of these tellurides, we propose a strategy for improving TE materials.
Chalcogenides containing elements from group 13 have attracted attention as thermoelectric materials, particularly compounds with crystal structures derived from the diamond structure, such as the zinc‐blende structure and the chalcopyrite structure. Specifically, a series of compounds that include CuGaTe2, CuInTe2, and AgGaTe2 has been found to exhibit high thermoelectric figure of merit (ZT) values at high temperatures. These chalcogenides are expected to attract increasing attention as novel thermoelectric materials in the future and to be the subject of much research aiming to determine the mechanism responsible for the high ZT and to further enhance the performance.
The temperature dependence of electrical conductivity, Seebeck coefficient, Hall coefficient, and thermal conductivity of Nb-doped MNiSn (M
=
Ti, Zr) half-Heusler compounds were investigated at ...different temperature, ranging from room temperature to 1000
K. The power factor reached 4
×
10
−3
Wm
−1
K
−2 above 600
K for both systems. The power factor for TiNiSn-based samples decreased above 700
K due to the narrower band gap. The Hall mobility was relatively small; however, estimated carrier effective mass was larger by one order of magnitude than that for conventional thermoelectric material. The thermal conductivity increased above 700
K due to the ambipolar diffusion effect. The ambipolar diffusion effect depended on the band gap width and the ratio of electron–hole conductivity. Heavy carrier-doping effectively suppressed the ambipolar diffusion effect, i.e. restrain the increase of thermal conductivity at high temperature. The maximum ZT value of 0.6 at 800
K was obtained for Zr
0.98Nb
0.02NiSn.
In this study, we have investigated the effect of planar defect on thermal and electron transport as compared to point defect in the rutile TiO2−x. Two series of bulk TiO2−x (2−x = 2.000, 1.992, ...1.985, 1.972, and 1.934) samples were prepared using different heat‐treatment procedures to clearly identify the presence of point and planar defects via powder X‐ray diffraction. The charge carrier density and mobility were determined from the Hall effect measurements using the van der Pauw method. The elastic properties of the studied materials such as bulk modulus, shear modulus, Young's modulus, compressibility, and Debye temperature were evaluated from the measured sound velocities, while their thermal conductivities were determined from the thermal diffusivities, heat capacities, and densities measured in the temperature range between 300 and 1073 K. The theoretical calculation based on Klemens‐Callaway model has been performed to analyze the thermal conductivity. As a result, the effect of planar defects on the carrier mobility was almost equivalent to the effect produced by point defects. On the other hand, the presence of planar defects significantly reduced the thermal conductivity of TiO2−x as compared to point defect due to strong phonon scattering induced by planar defects.
Tropical fruit crops are predominantly produced in tropical and subtropical developing countries, but some are now grown in southern Japan. Pineapple (Ananas comosus), mango (Mangifera indica) and ...papaya (Carica papaya) are major tropical fruits cultivated in Japan. Modern, well-organized breeding systems have not yet been developed for most tropical fruit species. Most parts of Japan are in the temperate climate zone, but some southern areas such as the Ryukyu Islands, which stretch from Kyushu to Taiwan, are at the northern limits for tropical fruit production without artificial heating. In this review, we describe the current status of tropical fruit breeding, genetics, genomics, and biotechnology of three main tropical fruits (pineapple, mango, and papaya) that are cultivated and consumed in Japan. More than ten new elite cultivars of pineapple have been released with improved fruit quality and suitability for consumption as fresh fruit. New challenges and perspectives for obtaining high fruit quality are discussed in the context of breeding programs for pineapple.
Nanostructuring is known to be an effective method to improve thermoelectric performance but, generally, it requires complex procedures and much labor. In the present study, self-assembled ...nanometer-sized composite structures of silicon (Si) and chromium disilicide (CrSi
2
) were easily fabricated by the rapid solidification of a melt with a eutectic composition. Ribbon-like samples were obtained with a dominant nanostructure of fine aligned lamellae with a spacing range of 20–35 nm. The thermoelectric power factor of the ribbon was observed to be 1.2 mW/mK
2
at room temperature and reached 3.0 mW/mK
2
at 773 K. The thermal conductivity was 65% lower than that of a bulk eutectic sample. The results suggest that this method is promising for fabricating an effective nanostructure for thermoelectric performance.
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