Rich structural phase diagram and thermoelectric properties of layered tellurides Mo1-xNbxTe2

MoTe2 is a rare transition-metal ditelluride having two kinds of layered polytypes, hexagonal structure with trigonal prismatic Mo coordination and monoclinic structure with octahedral Mo coordination. The monoclinic distortion in the latter is caused by anisotropic metal-metal bonding. In this work, we have examined the Nb doping effect on both polytypes of MoTe2 and clarified a structural phase diagram for Mo1-xNbxTe2 containing four kinds of polytypes. A rhombohedral polytype crystallizing in polar space group has been newly identified as a high-temperature metastable phase at slightly Nb-rich composition. Considering the results of thermoelectric measurements and the first principles calculations, the Nb ion seemingly acts as a hole dopant in the rigid band scheme. On the other hand, the significant interlayer contraction upon the Nb doping, associated with the Te p-p hybridization, is confirmed especially for the monoclinic phase, which implies a shift of the p-band energy level. The origin of the metal-metal bonding in the monoclinic structure is discussed in terms of the d electron counting and the Te p-p hybridization.Comment: 16 pages, 6 figures, 1 table, to be published in APL Material

Critical enhancement of thermopower in a chemically tuned polar semimetal MoTe2_{\bf 2}

Ferroelectrics with spontaneous electric polarization play an essential role in today's device engineering, such as capacitors and memories. Their physical properties are further enriched by suppressing the long-range polar order, as is exemplified by quantum paraelectrics with giant piezoelectric and dielectric responses at low temperatures. Likewise in metals, a polar lattice distortion has been theoretically predicted to give rise to various unusual physical properties. So far, however, a "ferroelectric"-like transition in metals has seldom been controlled and hence its possible impacts on transport phenomena remain unexplored. Here we report the discovery of anomalous enhancement of thermopower near the critical region between the polar and nonpolar metallic phases in 1T'-Mo$_{1-x}$Nb$_{x}$Te$_2$ with a chemically tunable polar transition. It is unveiled from the first-principles calculations and magnetotransport measurements that charge transport with strongly energy-dependent scattering rate critically evolves towards the boundary to the nonpolar phase, resulting in large cryogenic thermopower. Such a significant influence of the structural instability on transport phenomena might arise from the fluctuating or heterogeneous polar metallic states, which would pave a novel route to improving thermoelectric efficiency.Comment: 26 pages, 4 figure

Preference by Adult Female Riptortus Clavatus Thunberg for Plants from the Fabaceae and Other Plant Families

To obtain basic knowledge regarding the preference of adult female Riptortus clavatus for particular host plants, we investigated the preference of R. clavatus for green soybean, common bean, and cow pea as host plants, and between cow pea and either bell pepper, lettuce, cabbage, or cucumber. R. clavatus indicated a preference for cow pea over green soybean, followed by common bean. In addition, it was indicated that R. clavatus can distinguish among host plants. R. clavatus preferred cow pea over various non-host plants to a highly significant degree. These results clarified that adult female R. clavatus have strong ability to distinguish among host and non-host plants in the Fabaceae

Repellent Effect of Neem against the Cabbage Armyworm on Leaf Vegetables

We investigated the pest repellent effect of azadirachtin formulation and neem seed kernel oil cake. In laboratory tests, the repellent effect of komatsuna and spinach treated with azadirachtin formulation or neem seed kernel oil cake for 7 days on the feeding cabbage armyworm were evaluated. The feeding repellent effect of azadirachtin formulation treatment was equivalent to that of commercial biological pesticide, while the effect of neem seed kernel oil cake treatment was higher. This result clarified that neem seed kernel oil cake has a high feeding repellent effect against cabbage armyworms. In field tests, although the feeding percentage for komatsuna and spinach controls was 70%, that for komatsuna and spinach treated with azadirachtin formulation and neem seed kernel oil cake was about 40% and 30%, respectively. These laboratory and field test findings demonstrated that despite having an affect less than that of azadirachtin, neem seed kernel oil cake is a high effective feeding repellent

Walk-through programming for robotic manipulators based on admittance control

The present paper addresses the issues that should be covered in order to develop walk-through programming techniques (i.e. a manual guidance of the robot) in an industrial scenario. First, an exact formulation of the dynamics of the tool the human should feel when interacting with the robot is presented. Then, the paper discusses a way to implement such dynamics on an industrial robot equipped with an open robot control system and a wrist force/torque sensor, as well as the safety issues related to the walk-through programming. In particular, two strategies that make use of admittance control to constrain the robot motion are presented. One slows down the robot when the velocity of the tool centre point exceeds a specified safety limit, the other one limits the robot workspace by way of virtual safety surfaces. Experimental results on a COMAU Smart Six robot are presented, showing the performance of the walk-through programming system endowed with the two proposed safety strategies