Tetsuya Sasakawa

Structural, transport, and thermal properties of the single-crystalline type-VIII clathrate Ba8Ga16Sn30

The analysis of temperature dependence of mH suggests a crossover of a dominant scattering mechanism from ionized impurity to acoustic phonon scattering with increasing temperature. The existence of local vibration modes of Ba atoms in cages composed of Ga and Sn atoms is evidenced by analysis of experimental data of structural refinement and specific heat, which give an Einstein temperature of 50 K and a Debye temperature of 200 K. This local vibration of Ba atoms should be responsible for the low thermal conductivity s1.1 W / m K at 150 Kd. The potential of type-VIII clathrate compounds for thermoelectric application is discussed.

Thermoelectric properties of a clathrate compound Ba8Cu16P30

We report the electrical resistivity (ρ), thermoelectric power (S), thermal conductivity (κ), and specific heat (C) for the clathrate compound Ba8Cu16P30

Thermoelectric Properties of Valence-Fluctuating Eu Compound with a Clathrate-Like Structure, Eu3Pd20Ge6

We have found that in the series of R 3 Pd 20 X 6 (R=rare-earth element, X=Si or Ge), only Eu 3 Pd 20 Ge 6 shows valence-fluctuating behavior. The Eu atoms are caged in two kinds of polyhedra composed of Pd or Ge atoms, forming a clathrate-like structure. Since a rattling motion of the Eu atoms in the cages was expected, we have assessed the thermoelectric properties of Eu 3 Pd 20 Ge 6 by measuring its electrical resistivity, thermopower and thermal conductivity. Eu 3 Pd 20 Ge 6 shows good electrical conductivity. Reflecting the valence-fluctuating state, the thermopower reaches a maximum value of about 10 µV/K around 120 K. The thermal conductivity larger than 10 W/mK at high temperatures indicates a negligible rattling of Eu atoms.

75As NQR/NMR Study of Successive Phase Transitions and Energy Gap Formation in Kondo Semiconductor CeRhAs

75 As NQR/NMR studies were performed to investigate the successive phase transitions found recently, the gap formation and their interplay in a Kondo semiconductor CeRhAs. NQR/NMR spectra in their ...

Thermoelectric Properties of Binary Cd–Yb Quasicrystal and Its Approximant

The thermoelectric properties of the binary quasicrystal Cd84.6Yb15.4 and its approximant Cd6Yb are reported. The thermopowers decrease linearly from 14 and 12 µV/K, respectively, with decreasing temperature from 300 K. The resistivities at 300 K are 180 and 150 µΩcm, respectively, and decrease rapidly on cooling below 100 K. These results indicate that Cd–Yb compounds possess a metallic nature, in contrast to the semiconductor-like behavior of conventional ternary quasicrystals. The phonon thermal conductivity κph(T) of Cd–Yb compounds shows no maximum, but is described by a power law, κph∝Tn, with n=0.5 and 1.0, respectively, for Cd84.6Yb15.4 and Cd6Yb. The thermoelectric dimensionless figures of merit ZT are estimated to be 0.003 and 0.004 at 300 K, respectively.

Structural and Electronic Interplay in the Gap Formation in CeRhAs1-xSbx (0 ≤x ≤1)

Both CeRhAs and CeRhSb are known to open a narrow pseudogap at the Fermi level. For the alloys CeRhAs 1- x Sb x (0 ≤ x ≤1), we report the magnetic, transport and x-ray diffraction measurements. For...

Effects of La Substitution on the Energy Gaps and Superstructures of CeRhAs

Magnetic, transport and specific-heat measurements of Ce 1- x La x RhAs ( x ≤0.1) have been performed. The host compound CeRhAs undergoes successive phase transitions with formation of superlattices at T 1 =360, T 2 =235, and T 3 =165 K, respectively. The transitions at T 1 and T 3 are associated with the formation of a wide gap of E g1 / k B =2200 K and a narrow one of E g2 / k B =310 K, respectively. All anomalies at T 1 , which are a jump in the specific heat C , a drop in the magnetic susceptibility χ and the activation-type behavior in the Hall coefficient, remain until x is increased up to 0.10, at which T 1 is depressed to 297 K. These observations indicate that both the phase transition at T 1 and the gap of E g1 remain up to x =0.10. Anomalies in C and χ at T 2 and T 3 , on the other hand, vanish at a small concentration x =0.01. The semiconducting behavior in both the electrical resistivity and thermopower below T 3 also disappears at x =0.02. These facts corroborate that the narrow gap of E g2 ...

Thermoelectric Properties of Single-Crystal CeRhSn with Valence Fluctuations

The thermoelectric power S, electrical resistivity ρ and thermal conductivity κ have been measured for single crystals of CeRhSn and LaRhSn with the hexagonal ZrNiAl-type structure. For CeRhSn, a broad maximum of 60 µV/K appears in S(T) along both the a- and c-axes at 160 K, being typical of a valence-fluctuating Ce compound. The ρa(T) exhibits a high maximum of 350 µΩcm at 70 K, whereas ρc(T) decreases monotonically on cooling from 300 to 1.3 K. Although the measured κ(T) for CeRhSn is smaller than that for LaRhSn, the phonon contribution κph for the former is approximately twofold that for the latter. The relation κph(LaRhSn) < κph(CeRhSn) < κph(LaRhIn) suggests that the phonon scattering induced by atomic disorder is most significant in LaRhSn. The thermoelectric figure of merit Z for CeRhSn has the maxima of 3×10-4 K-1 at 160 K and 7×10-4 K-1 at 130 K along the a- and c-axes, respectively.

Double phase transitions in the heavy-fermion system Ce4Ni3Pb4

We report on the measurements of magnetic susceptibility χ, electrical resistivity ρ, specific heat C , and thermopower S of Ce 4 Ni 3 Pb 4 . This compound crystallizes in the trigonal (R3) La 4 Ni 3 Pb 4 -type structure, in which Ce atoms occupy two inequivalent sites. Both C ( T ) and ρ( T ) show anomalies at T M = 4 K and T N = 3 K, respectively. On the other hand, M / B =χ( T ) shows no anormaly at T M , but exhibits a considerable increase below T N . At 2 K, a hysteresis loop of magnetization has a small spontaneous moment, 2×10 -3 µ B /Ce. With increasing magnetic field, the ferromagnetic behavior in χ( T ) is suppressed and instead, a characteristic peak of an antiferromagnetic transition appears at B = 1 T. The weak ferromagnetism can be ascribed to the Dzyaloshinsky–Moriya interaction which may be present in Ce 4 Ni 3 Pb 4 without inversion symmetry. An extrapolation of the plot of C / T vs T 2 below 1 K yields γ= 200 mJ/(Ce mol K 2 ). Thus, this compound is a rare example of a Ce-based compound...

Crystal structure of the LaRhAs compound

Abstract The crystal structure of the new ternary pnicogenide LaRhAs, space group I41md (N109), a=4.187(2) A, c=14.950(2) A, Z=4, V=262.09 A, ρ=8.027 g cm−3, μ=34.51 mm−1 was refined to R=0.0585, wR2=0.1658 from the single-crystal X-ray diffraction data. This structure was confirmed by Rietveld refinement of the X-ray powder diffraction data. The LaRhAs compound is the first representative of the LaPtSi structure type among ternary pnictides of the rare-earths and transition metals.