Seiji Yoneda

Anomalous thermal expansion of Pb–Te system semiconductors

The thermal expansion properties of sintered samples of PbTe doped with 0.5 mass % PbI2 and those of Pb0.5Sn0.5Te were evaluated by two different methods such as: (1) by determining the apparent expansion coefficient obtained from dimensional changes and (2) by estimating the crystal lattice expansion coefficient calculated from the crystal lattice spacing. Abnormally large values of the apparent expansion coefficients were observed only for samples prepared from fine powders with a particle size of 25 μm or less at high temperatures above 400 °C, while such large values were not obtained for other samples in that temperature range. No significant differences were observed between the lattice expansion coefficients of the samples prepared from the fine powders and those of the other samples. Thermogravimetric analysis revealed that the abnormally large expansion developed in the crystal grain boundaries. The grain boundary effects were estimated by comparing the apparent expansion coefficients and the lat...

Anomaly in the specific heat of lead tellurides

Specific heats of two types of lead tellurides, namely p-type Pb1-xSnxTe (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) and n-type PbTe doped with y mass% PbI2 (y = 0.0, 0.2, 0.5, 0.8, 1.0), were observed in the temperature range of 50°C to 500°C using a differential scanning calorimeter (DSC). The specific heat of pure Te is also observed in the same temperature range to confirm the dominance of Te. At lower temperatures below 200°C, all the observed data were fairly consistent with those predicted on the basis of Dulong-Petit’s law, while above 200°C, the observed data showed curious temperature dependences. At high temperatures above 200°C, DSC analysis, with the aid of the experiment on pure Te, revealed an anomalously large specific heat that can be predicted from the Schottky defects caused by decomposition and sublimation of Te. In the n-type case, the anomaly in specific heats is rather smaller than that in the p-type case, which fact suggested that the dopant PbI2 may suppress the decomposition and sublimation of Te from lead tellurides.

Dissociation and sublimation of tellurium from the thermoelectric tellurides

Abstract The authors have recently reported that Te in Pb(1 − x)SnxTe (0 ≤ x ≤ 1) system compounds will be dissociated and sublimated at high temperatures over 400°C on the basis of experimental results. In the experiment, the thermal expansion was tested and the thermogravimetry-differential thermal analysis was carried out from the room temperature to 500°C. In the present work, a high-temperature X-ray diffraction profiles are observed to investigate the change in the crystal structure of PbTe and Bi2Te3. It is concluded from the experimental results that Te will be dissociated and move onto the sample surface to form a liquid or amorphous state at temperatures ranging from 200 to 400°C and that Te on the sample surface will be volatilised at higher temperatures than 400°C. It is also concluded that in Bi2Te3, Te might be sublimated even at lower temperatures than 400°C.

Pressure induced structural phase transition inAgSbTe2

We report a novel high pressure structural sequence for the functionally graded thermoelectric, narrow band gap semiconductor AgSbTe

Pressure induced structural phase transition in AgSbTe{sub 2}

_{2}

Temperature dependence of the figure-of-merit of Ag/sub 0.208/Sb/sub 0.275/Te/sub 0.517/

, using angle dispersive x-ray diffraction in a diamond anvil cell with synchrotron radiation at room temperature. The compound undergoes a B1 to B2 transition; the transition proceeds through an intermediate amorphous phase found between 17-26 GPa that is quenchable down to ambient conditions. The pressure induced structural transition observed in this compound is the first of its type reported in this ternary cubic family, and it is new for the B1-B2 transition pathway reported to date. Density Functional Theory (DFT) calculations performed for the B1 and B2 phases are in good agreement with the experimental results.

Structural Phase Transitions and Thermoelectric Properties of AgPb18SbTe20 Under Compression

We report a novel high pressure structural sequence for the functionally graded thermoelectric, narrow band gap semiconductor AgSbTe

Pressure induced structural phase transition in AgSbTe2

_{2}

Improved Thermoelectric Properties in Structure Controlled Ag-Sb-Te System

, using angle dispersive x-ray diffraction in a diamond anvil cell with synchrotron radiation at room temperature. The compound undergoes a B1 to B2 transition; the transition proceeds through an intermediate amorphous phase found between 17-26 GPa that is quenchable down to ambient conditions. The pressure induced structural transition observed in this compound is the first of its type reported in this ternary cubic family, and it is new for the B1-B2 transition pathway reported to date. Density Functional Theory (DFT) calculations performed for the B1 and B2 phases are in good agreement with the experimental results.

Possibility of improvement of thermoelectric properties of Pb1-xSnxTe by the Functionally Graded Material.

The p-type Ag/sub 0.208/Sb/sub 0.275/Te/sub 0.517/ boule was unidirectionally grown using a Bridgman furnace and subsequently rapidly cooled by Ar to form a Widmannstatten structure of a high temperature phase AgSbTe/sub 2/, which could be desirable for power generation. Though the boule looked a homogeneous Widmannstatten structure, XRD patterns revealed that some precipitates of Ag/sub 2/Te and Sb/sub 2/Te/sub 3/ were contained in the boule and increased in volume in the growth direction. The figure-of-merit Z of the p-type Ag/sub 0.208/Sb/sub 0.275/Te/sub 0.517/ boule have been evaluated in the temperature range from 300 to 700 K. The maximum figure-of-merit Z/sub max/ was different in the portions of the boule. The value of 2.0/spl times/10/sup -1//K was at 620 K for the former half portion of the boule and that of 1.7/spl times/10/sup -3//K was at 585 K for the latter half portion. The Ag/sub 0.208/Sb/sub 0.275/Te/sub 0.517/ boule with less precipitates showed higher Z at higher temperatures.