Search

The thermoelectric properties of the samples were investigated along with their microstructures. The results show that the plasma treatments reduced thermal conductivity and increased electrical conductivity and mobility, which led to an increase in thermoelectric figure of merit.

This clathrate had a maximum dimensionless figure-of-merit, ZT, of 0.93 at 637 K, which was slightly higher than that of 0.83 for the sintered type-VIII clathrate Ba8Ga16Sn30. We investigated the high-temperature thermoelectric properties, transport properties, electronic structures, and thermal stabilities of the clathrates. The type-II clathrate was found to be superior to the type-VIII clathrate as a thermoelectric material; it had a high thermal stability and melting point, 859 K, high mobility, 141 cm2V-1s-1 at 300 K, because of its low inertial mass, and low high-temperature lattice thermal conductivity, approximately 4 mW cm-1K-1, resulting from a larger unit cell and weaker bipolar thermal conduction. We discuss these properties in terms of the electronic structure and the differences between the two types of clathrate. [ABSTRACT FROM AUTHOR]

To reduce the magnetic field amplitude required to orient guanine crystal plates, we have attached magnetic nanoparticles to these guanine crystal plates. Fe2O3 nanoparticles are mixed with the guanine crystal plates, which are dispersed in water. Observation by optical microscopy confirmed that the large particles, which are nanoparticle aggregates, attach preferentially to the side edges of the guanine crystal plates. The individual crystal plate surfaces show clear, undisturbed light interference patterns, which mean that each plate's optical properties have been maintained. The magnetic orientation experiments of these guanine crystal plates with different numbers of optically observed particles are conducted under both in-plane and vertical magnetic fields. The positions of the attached particles do not change, even when the magnetic field is applied. In these experiment, it was difficult to align the crystal direction with the magnetic field direction because the magnetic orientation characteristics are strongly affected by the positions and numbers of the attached particles. However, in-plane rotation and an increased tilt angle are achieved for the guanine crystal plates using magnetic fields of several millitesla. [ABSTRACT FROM AUTHOR]

Nominal Sr8AlxGa16-xGe30 samples with x=6, 8, and 10 crystallized in the type-VIII clathrate structure (I43m, No. 217), while the sample with x=4 crystallized in the type-I clathrate structure (Pm3n, No. 223). While a large number of the type-I thermoelectric clathrates exist, only three type-VIII clathrates of Ba8Ga16Sn30, Eu8Ga16Ge30, and Sr8AlxGa16-xSi30 had been synthesized before. The type-VIII Sr8AlxGayGe46-x-y samples (6≤x≤7 and 10≤y≤11) with various carrier concentrations were prepared to investigate their thermoelectric properties. They exhibited the temperature dependences of electrical conductivities and the Seebeck coefficients typical of n type degenerate semiconductors, which almost depended on their carrier concentrations systematically. A relatively large dimensionless figure-of-merit ZT of 0.56 at 800 K was obtained for the type-VIII Sr8Al6.3Ga10.3Ge29.4 sample with a carrier concentration of 3.0×1020 cm-3. This ZT value is comparable to that of 0.62 at 800 K for the type-I Sr8Ga16.5Ge29.5 clathrate. The type-VIII clathrate had a smaller effective mass, a higher mobility, and a higher lattice thermal conductivity than those of the type-I clathrate. The difference in transport properties between the type-I and type-VIII clathrates is also discussed. [ABSTRACT FROM AUTHOR]

Raman scattering and x-ray diffraction (XRD) measurements of iodine-doped cationic type-I clathrate I8Sb8Ge38 have been carried out at 1 bar and high pressures of up to 50 GPa at room temperature, by using a diamond anvil cell. The guest-iodine rattling vibrations were observed in a low-frequency region of 53–58 cm-1 at ambient conditions as well as the host vibrations in a higher-frequency region of 75–273 cm-1. High-pressure Raman spectroscopy showed the frequency softening of iodine rattling vibrations at pressures above 16 GPa, which originates from the weakening of guest-host interactions due to the transfer of electrons from the large-size guest I to the framework. High-pressure Raman and XRD studies revealed that the amorphization proceeds gradually around 36–44 GPa and is completed at about 50 GPa. The isostructural phase transition with a volume reduction was observed at 42 GPa, which is compared with other type-I Ge clathrates. [ABSTRACT FROM AUTHOR]

Thermoelectric properties of Al-substituted Ge clathrate compounds Ba8AlxGe46-x were investigated experimentally and theoretically. Polycrystalline Ba8AlxGe46-x (x=12–18) was synthesized by using an arc melting and a spark plasma sintering technique. The obtained samples show the n-type behavior and the carrier concentration decreases with increasing amount of Al composition from x=12 to 16. The reasonably large power factors was obtained: 900–1000 μW/cm K2 around 900 K. Theoretically electronic structure of Ba8Al16Ge30 was calculated by means of a first-principles method and then thermoelectric properties were analyzed on the basis of the result of the calculated electronic structure. The calculated thermoelectric properties agree with the experimental results very well in the wide range of temperature between room temperature and 900 K. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of FeTe2 substituted with Co were prepared by powder metallurgy, and their thermoelectric properties were investigated. When the substitution amount x increased to 0.4, their electrical conductivity increased to approximately 2000 S/cm at room temperature and their lattice thermal conductivity decreased to 10 mW cm-1 K-1 at high temperatures. A maximum dimensionless figure of merit of 0.13 was obtained for Fe0.8Co0.2Te2 at 700 K. The electronic structure of FeTe2 was also calculated, and the possibility of improving its thermoelectric performance of FeTe2 is discussed. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of Sr8GaxGe46-x clathrates with varied nominal Ga contents were prepared by powder metallurgy to produce n-type samples with carrier concentration n of 1.8×1020–1.1×1021 cm-3. Their thermoelectric properties were measured in the temperature range from 300 to 900 K. Their Seebeck coefficient and electrical conductivity were found to be typical for a heavily doped semiconductor, and varied systematically with their carrier concentration. The maximum value of the figure-of-merit ZT was 0.62 at 800 K for n=5.6×1020 cm-3. Other following properties were also measured or estimated, and their relationships with the thermoelectric properties are discussed. The band gap of the samples was estimated to be 0.4–0.5 eV; their effective mass was an almost constant value of 3.1me at room temperature, and this value decreases with increasing temperature; and their electron Hall mobilities were 8–13 cm2 V-1 s-1 at room temperature, increasing slightly with decreasing carrier concentration. [ABSTRACT FROM AUTHOR]

Thermoelectric properties of polycrystalline degenerate n-type PbTe films have been investigated in order to understand potential barrier scattering. The Seebeck coefficients of the PbTe films obtained in this study were larger than those of bulk samples having the same carrier concentrations in the temperature range from 100 to 450 K. Some of their power factors were larger than those of bulk samples having the same carrier concentrations in the temperature range from 200 to 450 K, while their electrical conductivities were smaller than those of bulk samples. From a comparison of these results with those previously reported, we concluded that potential barrier scattering occurred at grain boundaries in our films, resulting in the above favorable changes in thermoelectric properties. By analyzing their properties using the energy filtering model, we estimated the height of grain-boundary potential barriers, which probably influenced the increases in the Seebeck coefficient. We also examined the origin of the potential barriers accordingly. Consequently, we consider that the origin of the potential barriers was mainly due to point defects, probably Te vacancies, and that the barrier height may be controlled, for example, by the preparation conditions. [ABSTRACT FROM AUTHOR]

Microstructural control by means of plasma treatment was performed on sintered Cr-doped β-FeSi[SUB2] in order to improve its thermoelectric properties. The micrograins were exposed to rf plasmas of germane (GeH[SUB4]) or a mixture of germane and silane (SiH[SUB4]) and were then sintered. The thermoelectric properties of the samples were investigated along with their microstructures. The results show that the plasma treatments reduced thermal conductivity and increased electrical conductivity and mobility, which led to an increase in thermoelectric figure-of-merit. In addition, the results show that the plasma treatments also formed small SiGe crystals distributed throughout the samples, removed most of the grain boundaries, and sometimes formed FeSi crystals. The relation between the changes in the thermoelectric properties and the modification of the microstructure was discussed. It was found that the microstmctural modification by the plasma treatment caused favorable changes in thermoelectric properties. [ABSTRACT FROM AUTHOR]

Sintered degenerate n-type PbTe samples with small grain sizes ranging from 0.7 to 4 µm were prepared and the effects of grain size on their thermoelectric properties were then investigated. The Seebeck coefficient of the sintered samples increased almost double when the grain size decreased from 4 to 0.7 µm. On the other hand, their electrical and thermal conductivity decreased with decreasing grain size. Accordingly, decreasing their grain size increased their thermoelectric figure-of-merit. A maximum value of the figure-of-merit of the obtained small grain-size samples was significantly higher than that of large grain-size samples with the same carrier concentration reported. This favorable result was caused mainly by the increase in the Seebeck coefficient. The influences of grain boundaries on the increase in the Seebeck coefficient were discussed. It is concluded that the Seebeck coefficient was increased by potential barrier scattering, which occurred at the grain boundaries in the sintered samples. [ABSTRACT FROM AUTHOR]

The type-VIII [Sr.sub.8][Al.sub.x][Ga.sub.y][Ge.sub.46-x-y] samples with various concentrations are prepared to examine their thermoelectric properties. The type-VIII clathrate had a smaller effective mass, a higher mobility and a higher lattice thermal conductivity than those of the type-I clathrate and the difference in transport properties between the type-I and type-VIII clathrates is discussed.

Raman scattering and x-ray diffraction (XRD) measurements of iodine-doped cationic type-I clathrate [I.sub.8][Sb.sub.8][Ge.sub.38] are carried out at high pressures at room temperature by using a diamond anvil cell. The studies have shown that the amorphization has proceeded gradually around 36-44 GPa and the isostructural phase transition with a volume reduction is observed at 42 GPa.

Thermoelectric properties of Al-substituted Ge clathrate compounds [Ba.sub.8][Al.sub.x][Ge.sub.46-x] are examined. The studies have shown that the thermoelectric properties can be improved by controlling the carrier concentration.

Polycrystalline samples of Fe[Te.sub.2] substituted with Co are prepared by powder metallurgy and their thermoelectric properties are investigated. The substitution of Co for Fe has increased the electron carrier concentration, leading to the increase in their electrical conductivity, and has also caused alloy scattering of phonons, decreasing their lattice thermal conductivity.

Polycrystalline samples of [Sr.sub.8][Ga.sub.x][Ge.sub.46-x] clathrates with various carrier concentrations are prepared and their thermoelectric and transport properties are measured. The band gap of the samples is estimated to be 0.4-0.5 eV, their effective mass is a constant value of 3.1 [m.sub.e] at room temperature which decreases with increasing temperature and their electron Hall mobilities are 8-13 [cm.sup.2] [V.sup.-1] [s.sup.-1] at room temperature, increasingly slightly with decreasing carrier concentration.

The light reflection intensity from a biogenic guanine crystal that shows strong light scattering on the broadest surface of the crystal can be modulated by the magnetic field switching due to the dynamic motion of magnetic orientation caused by the diamagnetic anisotropy. Magnetic field amplitudes required for magnetic orientation are drastically decreased by hybridizing the guanine crystal with a ferromagnetic thin film, which is one of the important factors for device application from the viewpoint of power consumption and field generation method. In this paper, we present the 3-D magnetic orientation control of the guanine crystal hybridized with the 5 nm thick permalloy film by applying the magnetic field with a three-axis Helmholtz coil. Vertical magnetic field dependences of the tilt angle of (102) plane of the guanine crystal from the substrate for various in-plane magnetic fields are investigated. It is clarified that the hybrid plate can be controlled three-dimensionally with the magnetic field less than several milliteslas by applying the suitable in-plane field. It is shown that the hybrid plate floating under water is transported by the magnetic field gradient using the permanent magnet, which is effective for carrying it to the target position. The 3-D magnetic orientation characteristics of the hybrid plate that shows the similar behavior to the biogenic guanine crystal for the vertical magnetic field are also mentioned. [ABSTRACT FROM AUTHOR]

Focuses on a study that investigated the epitaxial growth of cadmium[sub 1-x]manganese[sub x]tellurium films with x ranging from 0 to 0.76 on sapphire substrates using the ionized-cluster beam method. Experimental procedure; Results and discussions; Conclusion.

Presents a study which examined the magneto-optical Kerr effect of rf sputtering and subsequent annealing to assess the high magneto-optical Kerr effect of the compound. Materials and methods; Experimental results; Discussion.

This paper focuses on the light interference in biogenic guanine crystals that have interesting optical properties such as high reflectivity and optical biaxiality. In this paper, we find that a Moiré effect pattern is generated on a single guanine crystal of goldfish combining with the mirror surface substrate. An observation system, in this paper, is consisted with telecentric lens and coaxial vertical illumination using blue LED light source. It is clearly seen that homogeneous light and shade stripe patterns are observed on the broadest surface of the single guanine crystal plate floating in water. By contrast, when the guanine crystals are set on the substrates having the diffused reflection surface, this light and shade stripe pattern is not observed on the single guanine crystal but observed on two cross-stacked crystals as reported before. These results show that the light and shade stripe pattern on the single guanine crystal is produced by the optical interference, so-called Moiré effect, between guanine crystal and the mirror substrate surface. The angle dependence of reflection brightness and the magnetic orientation of guanine crystal are investigated by using Moiré patterns. Furthermore, we demonstrate that small curvatures and steps can be optically detected and estimated by the pattern change of Moiré stripes. It is confirmed that the direction of curvature is detected by controlling the guanine crystal orientation with magnetic fields and the curvature shape is reproduced from the Moiré pattern. [ABSTRACT FROM AUTHOR]

In micro-optical device and micro-electromechanical systems applications, the driving power and response time are the important factors for their performance. In this paper, a diamagnetic guanine crystal/ferromagnetic film hybrid plate is fabricated by the sputtering method in order to decrease the magnetic field amplitude required for the guanine crystal orientation. The behavior of the hybrid plate having a 5 nm-thick permalloy film in water under magnetic fields is investigated by using a three-axis Helmholtz coil. The hybrid plate rotates according to the horizontal magnetic field so that the length of (102) plane of guanine crystal is parallel to the field direction. For the vertical magnetic field, the hybrid plate easily stands up. These behaviors are attributed to the large shape anisotropy of ferromagnetic film of hybrid plate. Magnetic field amplitudes required for magnetic orientation drastically decrease compared to those for diamagnetic orientation of the pure guanine crystal. It has been demonstrated that LED lights which are simultaneously irradiated from different directions can be selectively introduced into the microscope by using the reflection of hybrid plate which is controlled with external magnetic fields. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the electro-optical properties of Cd[sub1-x]Mn[subx]Te films prepared through the ionized-cluster beam deposition technique. Illustration of the electro-optical birefringence of such films; Factor responsible for the electro-optical properties of the films; Investigation on the electro-optical effects of various compound semiconductors.

Polycrystalline clathrate samples of nominal K8GaxSn46−xwere prepared by the spark plasma sintering method to investigate their crystal structures, mobilities and thermoelectric properties. The samples almost had a single-phase type-I clathrate structure, and their relative densities reached as high as 98%. The room-temperature mobility of the K8Ga8Sn38sample was 25 cm2V−1s−1, which substantially exceeded the reported mobilities of Rb- and Cs-containing Sn clathrates. Moreover, the mobility was larger than those of the type-I Ba8Ga16Sn30, which had more Ga substituting atoms in unit cell. A higher mobility might accordingly be achieved in thermoelectric clathrates with a smaller number of substituting atoms. Their electrical conductivities and Seebeck coefficients in the temperature range 300–450 K were typical of n-type doped semiconductors in the extrinsic region while their room-temperature lattice thermal conductivities were as low as ∼11 mW cm−1K−1. The maximum dimensionless figure of merit ZTwas estimated to be 0.27 at 490 K from the Seebeck coefficient of −262 μV K−1and the electrical conductivity of 96 S cm−1for the K8Ga8Sn38sample with a carrier concentration of 2.9 × 1019cm−3 [ABSTRACT FROM AUTHOR]

Abstract: Li-filling in tetrahedral InSb and related compounds was attempted to investigate its effect on their thermal conductivities. Li-filled Li0.2In0.8Zn0.2Sb, Li0.4In0.6Zn0.4Sb, LiZnSb, and Li0.16Ga0.84Zn0.16Sb sintered samples were prepared by powder metallurgy. The filled samples had much lower room temperature lattice thermal conductivities than those of the corresponding unfilled materials; the values of the Li0.4In0.6Zn0.4Sb, LiZnSb, and Li0.16Ga0.84Zn0.16Sb were 23, 45, and 72 mW cm−1K−1, respectively. Filled tetrahedral compounds such as Li x In1−x Zn x Sb might be good thermoelectric materials. [Copyright &y& Elsevier]

The tellurium-containing cationic type-I clathrate Ge30P16Te8 was synthesized and its thermoelectric properties were investigated. This clathrate showed a p-type conductivity, while most of the clathrates are n type. The Ge30P16Te8 clathrate had a band gap energy of 0.62 eV and a room temperature thermal conductivity of 9 mW cm-1 K-1, which is as low as those of germanium clathrates such as anionic Sr8Ga16Ge30 and cationic Ge38Sb8I8. The electronic structure of the Ge30P16Te8 clathrate was also calculated using an ab initio method. [ABSTRACT FROM AUTHOR]

The iodine-containing cationic type-I clathrates Ge38Sb8I8 and Sn38Sb8I8 were prepared and their thermodynamic properties as well as their thermoelectric properties were investigated. Their atomic displacement parameters were as large as those of anionic clathrates such as Ba8Ga16Ge30 and Cs8Cd4Sn42. The room temperature thermal conductivities of Ge38Sb8I8 and Sn38Sb8I8 were 7 and 12 mW cm-1 K-1, respectively; these values were as low as that of the above anionic clathrates. Both cationic clathrates had negative Seebeck coefficients; the band gap energies of Ge38Sb8I8 and Sn38Sb8I8 were 1.16 and 0.80 eV, respectively. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of degenerate n-type KxBa8-xZnyGe46-y (y∼8-x/2) with the type-I clathrate structure (No. 223, Pm3n) were prepared by powder metallurgy to obtain a high-efficiency Ge-based clathrate. Their Zn atoms preferred to exist at the 6c site in the framework, and consequently, the samples with x around 4, such as K4Ba4Zn6Ge40, possessed highly ordered Zn/Ge atom frameworks whose 6c, 16i, and 24k sites were occupied almost solely by Zn, Ge, and Ge atoms, respectively. In spite of such ordered structures and small numbers of substituting Zn atoms, these samples exhibited carrier mobilities lower than those of Ba8Zn8Ge38 and Ba8Ga16Ge30. Band structure calculations implied that the combination of the rattler K and Ba atoms in the cages considerably modified the conduction band edge of the corresponding clathrates; such a modification is considered to strengthen alloy disorder scattering, which reduces carrier mobility. The maximum dimensionless figure-of-merit ZT was 0.51 at 1000 K for the K2Ba6Zn7Ge39 sample, which is similar to that of 0.50 at 900 K for the Ba8Zn8Ge38 sample. [ABSTRACT FROM AUTHOR]

Nominal Sr8AlxGa16-xGe30 samples with x=6, 8, and 10 crystallized in the type-VIII clathrate structure (I43m, No. 217), while the sample with x=4 crystallized in the type-I clathrate structure (Pm3n, No. 223). While a large number of the type-I thermoelectric clathrates exist, only three type-VIII clathrates of Ba8Ga16Sn30, Eu8Ga16Ge30, and Sr8AlxGa16-xSi30 had been synthesized before. The type-VIII Sr8AlxGayGe46-x-y samples (6≤x≤7 and 10≤y≤11) with various carrier concentrations were prepared to investigate their thermoelectric properties. They exhibited the temperature dependences of electrical conductivities and the Seebeck coefficients typical of n type degenerate semiconductors, which almost depended on their carrier concentrations systematically. A relatively large dimensionless figure-of-merit ZT of 0.56 at 800 K was obtained for the type-VIII Sr8Al6.3Ga10.3Ge29.4 sample with a carrier concentration of 3.0×1020 cm-3. This ZT value is comparable to that of 0.62 at 800 K for the type-I Sr8Ga16.5Ge29.5 clathrate. The type-VIII clathrate had a smaller effective mass, a higher mobility, and a higher lattice thermal conductivity than those of the type-I clathrate. The difference in transport properties between the type-I and type-VIII clathrates is also discussed. [ABSTRACT FROM AUTHOR]

Structural properties of hydrothermally deposited PbTiO3 films have been investigated. The films were synthesized in the temperature range from 120 to 180 °C for 24 h. X-ray diffraction (XRD) analysis indicates that all of the deposited films exhibited the tetragonal perovskite single phase. However, 001 diffraction peaks broadened in comparison with 100 diffraction peaks. Structural characterization showed that the films had two regions with different crystallinities. In one region, the PbTiO3 crystals had a relatively high crystallinity and grew with a preferred orientation in the (001) direction. Furthermore, in this region, the crystallinity of the crystals deposited at a temperature as low as 120 °C was similar to that of the crystals deposited at 180 °C. On the other hand, the PbTiO3 crystals in another region exhibited a low crystallinity and a random orientation. Consequently, the broadening of the 001 diffraction peaks can be explained by the mixed structure of the two regions with different crystallinities. [ABSTRACT FROM AUTHOR]

Nominal composition Sr8AlxGa16-xSi30 (0≤x≤16) samples were prepared by powder metallurgy. The samples with x=0–7 exhibited the type-I clathrate structure (Pm3n, No. 223), while the samples with x=8–13 almost exhibited the type-VIII clathrate structure (I43m, No. 217). These samples possessed the electrical conductivities and Seebeck coefficients typical of n-type degenerated semiconductors. The results on their thermoelectric properties indicate that the type-VIII SrAlGaSi clathrate would be a more efficient thermoelectric material than the type-I SrAlGaSi clathrate. For example, the type-VIII Sr8Al9Ga7Si30 sample had a maximum power factor of 11 µW cm-1 K-2 at 1000 K and a room temperature Hall mobility of 24 cm2 V-1 s-1, while those of the type-I Sr8Al6Ga10Si30 sample were 7 µW cm-1 K-2 and 5 cm2 V-1 s-1, respectively. [ABSTRACT FROM AUTHOR]

The iodine-containing cationic type-I clathrates Ge38Sb8I8 and Sn38Sb8I8 were prepared and their thermodynamic properties as well as their thermoelectric properties were investigated. Their atomic displacement parameters were as large as those of anionic clathrates such as Ba8Ga16Ge30 and Cs8Cd4Sn42. The room temperature thermal conductivities of Ge38Sb8I8 and Sn38Sb8I8 were 7 and 12 mW cm-1 K-1, respectively; these values were as low as that of the above anionic clathrates. Both cationic clathrates had negative Seebeck coefficients; the band gap energies of Ge38Sb8I8 and Sn38Sb8I8 were 1.16 and 0.80 eV, respectively. [ABSTRACT FROM AUTHOR]

Thermoelectric properties of Al-substituted Ge clathrate compounds Ba8AlxGe46-x were investigated experimentally and theoretically. Polycrystalline Ba8AlxGe46-x (x=12–18) was synthesized by using an arc melting and a spark plasma sintering technique. The obtained samples show the n-type behavior and the carrier concentration decreases with increasing amount of Al composition from x=12 to 16. The reasonably large power factors was obtained: 900–1000 μW/cm K2 around 900 K. Theoretically electronic structure of Ba8Al16Ge30 was calculated by means of a first-principles method and then thermoelectric properties were analyzed on the basis of the result of the calculated electronic structure. The calculated thermoelectric properties agree with the experimental results very well in the wide range of temperature between room temperature and 900 K. [ABSTRACT FROM AUTHOR]

The tellurium-containing cationic type-I clathrate Ge30P16Te8 was synthesized and its thermoelectric properties were investigated. This clathrate showed a p-type conductivity, while most of the clathrates are n type. The Ge30P16Te8 clathrate had a band gap energy of 0.62 eV and a room temperature thermal conductivity of 9 mW cm-1 K-1, which is as low as those of germanium clathrates such as anionic Sr8Ga16Ge30 and cationic Ge38Sb8I8. The electronic structure of the Ge30P16Te8 clathrate was also calculated using an ab initio method. [ABSTRACT FROM AUTHOR]

Polycrystalline clathrate samples of nominal K(8)Ga(x)Sn(46-x) were prepared by the spark plasma sintering method to investigate their crystal structures, mobilities and thermoelectric properties. The samples almost had a single-phase type-I clathrate structure, and their relative densities reached as high as 98%. The room-temperature mobility of the K(8)Ga(8)Sn(38) sample was 25 cm(2) V(-1) s(-1), which substantially exceeded the reported mobilities of Rb- and Cs-containing Sn clathrates. Moreover, the mobility was larger than those of the type-I Ba(8)Ga(16)Sn(30), which had more Ga substituting atoms in unit cell. A higher mobility might accordingly be achieved in thermoelectric clathrates with a smaller number of substituting atoms. Their electrical conductivities and Seebeck coefficients in the temperature range 300-450 K were typical of n-type doped semiconductors in the extrinsic region while their room-temperature lattice thermal conductivities were as low as approximately 11 mW cm(-1) K(-1). The maximum dimensionless figure of merit ZT was estimated to be 0.27 at 490 K from the Seebeck coefficient of -262 microV K(-1) and the electrical conductivity of 96 S cm(-1) for the K(8)Ga(8)Sn(38) sample with a carrier concentration of 2.9 x 10(19) cm(-3).