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Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi-2212) superconducting single crystals were prepared by a modified vertical Bridgman method using large crucibles of a 30 mm external diameter with a cone-shaped bottom. In order to obtain a large single crystal with high crystallinity, we optimized the growth conditions, where the large crucibles were used. As a result, we could obtain a large plate-like single crystal with a size of 17.0 × 5.5 mm 2 when the rotation speed of crucible and the starting temperature of melt for crystal growth were 50 rpm and 1000 °C, respectively. The full width at half maximum value of the (0 0 1 0 ) X-ray diffraction peak due to Bi-2212 was small with about 0.06°. Moreover, the critical temperature ( T c ) of the single crystals was about 87 K, which was higher than the T c of the single crystals grown with the crucibles whose external diameter was by 30% smaller than that of the large crucibles.

The effect of magnetic field on the pseudogap in the Kondo semimetal CeNiSn has been reinvestigated by the measurement of magnetization and longitudinal magnetoresistance in pulsed high magnetic fields applied along the principal crystallographic directions of the orthorhombic structure. By extending the field range up to 65 T, metamagnetic behaviors at 45 and 60 T are observed for the first time along the easy magnetization direction of a -axis. No anomaly is found, on the other hand, along the b - and c -axes up to 55 T. The magnetoresistance along the a -axis exhibits the minimum at about 30 T and increases above 40 T, which is in accord with the anomalous increase of the magnetization. By contrast, the magnetoresistance along the b - and c -axes shows only a monotonous decrease above 10 T. These results are discussed in terms of a Zeeman splitting of the double-gapped density of states derived from the anisotropic hybridization-gap model.

Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ (Bi-2212) superconducting single crystals were prepared by a modified vertical Bridgman method using large alumina crucibles of a 26 mm bore diameter with cone-shaped bottom. In order to obtain large and high quality single crystals, we optimized growth conditions using the large crucibles. We obtained a large plate-like single crystal with a size of 17.0 mm /spl times/ 5.5 mm when the crystal growth was carried out with the rotation speed of 50 rpm and at the temperature for starting the crystal growth of 1000/spl deg/C. In the single crystal, the FWHM value of the (0010) x-ray diffraction peak which was assigned to a Bi-2212 superconductor was small and about 0.06/spl deg/. T/sub c/ of the single crystal was about 87 K, which was higher than T/sub c/=82 K of the single crystals grown with smaller crucibles whose bore diameter is 35% less than the large crucibles.

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.

We report a systematic study of thermoelectric properties of a series of Ce-based compounds with the e -TiNiSi-type structure; metallic CePtSn, semimetallic CeNiSn and CeRhSb, and semiconducting CeRhAs. In this sequence, both the Kondo temperature and hybridization-gap width increase, whereas the phonon thermal conductivity at high temperatures decreases. Opening of the pseudogap in CeRhSb and CeRhAs enlarges the thermopower, and leads to the maxima of the thermoelectric figure of merit, 1.7×10 −3 /K at 12 K and 1.0×10 −3 /K at 115 K, respectively.

We present measurements of the electrical resistivity ρ(T) on high-quality single-crystalline CeNiSn under both hydrostatic pressure up to 1 GPa and uniaxial pressure up to 0.25 GPa. At ambient pressure, ρ(T) along the orthorhombic a-axis (b-axis) shows two maxima at TL = 12 K (14 K) and TH = 74 K (40 K), respectively, which arise from the Kondo scattering of conduction electrons by the crystal-field ground state and excited states. With increasing hydrostatic pressure, both TL and TH increase linearly, and for P≥0.8 GPa, the anisotropy in ρ(T) for I∥a and I∥b almost vanishes as a result of increased hybridization between the 4f electrons and the conduction electrons. Under P∥a, both TL and TH in ρ(I∥b) increase similarly to under hydrostatic pressure. Under P∥c, however, the depression of TL in ρ(I∥a) and ρ(I∥b) suggests that the c-f hybridization in the crystal-field ground state is weakened in the a-b plane of CeNiSn.

Structural studies by means of powder X-ray diffraction and single-crystal neutron diffraction show that URhGe crystallizes in the orthorhombic TiNiSi-type of structure. Combined magnetic, electrical-transport and thermal studies performed for the first time on a single crystal confirm ferromagnetic order of URhGe below 9.6 K. In contrast to previous powder neutron-diffraction experiments, our single-crystal results point to collinear ferromagnetic order of U moments of 0.35±0.08 μ B confined to the b–c plane, i.e. with no component along the a -axis, which is the hard-magnetization direction in URhGe. Our findings regarding the magnetic properties are in good agreement with theoretical first-principle calculations.

We have performed magnetoresistance measurements on an organic conductor, α-(BEDT-TTF)2KHg(SCN)4, and on a Kondo semiconductor, CeNiSn, at low temperatures and for fields up to 45 T in the hybrid magnet at the National High Magnetic Field Laboratory. We will discuss some new insight into a very controversial high-field phase of α-(BEDT-TTF)2KHg(SCN)4 gained from measurements of the anomalous temperature dependence of the quantum oscillations in the range 25–45 T. New information will also be presented on the temperature dependence of resistivity in the high-field state of CeNiSn, where questions of metallic versus semiconducting ground states arise. To acquaint researchers who anticipate using the facility in the near future, practical details concerning use of this new high-field resource are included.

We have studied a metamagnetic-like anomaly in CeNiSn via measurements of transverse and longitudinal magnetoresistance (MR) and AC magnetic susceptibility (χ) in a wide range of temperature T, magnetic field B, and pressure p, i.e., 0.05 K⩽ T ⩽0.9 K , 0⩽ B ⩽20 T , and 0⩽ p ⩽10 kbar . We identify five field regions in which both MR and χ exhibit anomalous behavior, i.e., distinct deviation from monotonous variation as a function of B. The disparate pressure dependence of each regime cannot be explained by the pressure variation of a single parameter, viz., the Kondo temperature, and suggests that the metamagnetic-like anomaly in CeNiSn is a combination of anomalies of different origins.

The thermoelectric power S was measured from 1.5 to 500 K for CePdSb, CeRhSn, CeIrSn, UNi4B, UPt2In and UCu3+xGa2−x. The value of S at 300 K ranges from 16 to 70 μV/K. The rather large S is attributed to the strong scattering of conduction electrons by the 4f or 5f electrons in the vicinity of the Fermi level. A Lorentzian 4f-band model, which was previously proposed for valence fluctuating compounds, reproduces the temperature dependence of S for CeRhSn and CeIrSn. However, it can not reproduce the upward curvature of S(T) at low temperatures for the U compounds. We propose here a two-5f-bands model, which consists of a narrow (5–20 meV) and a wide (37–82 meV) Lorentzian density of states. The good fitting to the data of S(T) for the above U compounds suggests the presence of two energy scales.

We report on the magnetic, transport and thermal measurements for a single-crystal sample of CeNi0.82Cu0.18Sn. An antiferromagnetic order below T N =3.5 K is observed in magnetic susceptibility χ, specific heat C and electrical resistivity. The specific heat jump at TN is only 0.7 J/mol K and a large value of C/T=380 mJ/mol K 2 remains at 0.5 K. The strong magnetic anisotropy, χ a >χ b >χ c , is similar to that for the host compound CeNiSn. From the analysis of χ(T), we derived a set of crystal-field parameters, which yield the ground state consisting mainly of |J Z 〉=|±5/2〉.

Magnetic order (including spin freezing) is absent down to ∼15 mK in CeNiSn due to the dominance of coherent spin fluctuations caused by the Kondo interaction. Partial replacement of Ni by Cu or Pt induces a highly disordered magnetic state. The critical concentration is much lower for Cu replacement (∼7%) than for Pt replacement (∼30%). Results of μSR and specific heat (for CeNi 1− x Cu x Sn) measurements near the critical concentration are presented. The possibility of a quantum critical point is discussed. A tentative phase diagram for the two parameters relevant for the onset of magnetism, the unit cell volume and the d electron density, is derived.

We report the observation of an unexpected magnetic transition in the Kondo semimetal CeNiSn under uniaxial pressures. For $P\ensuremath{\parallel}a,$ both the specific heat C and magnetic susceptibility \ensuremath{\chi} decrease steadily with increasing P. By contrast, once $P\ensuremath{\parallel}b$ and $P\ensuremath{\parallel}c$ exceed 0.13 GPa, $C(T)$ exhibits a distinct jump at 4 K followed by a peak at 3 K. The concomitant peaking in $\ensuremath{\chi}(T)$ for $P\ensuremath{\parallel}B\ensuremath{\parallel}c$ is indicative of an antiferromagnetic transition.

Superconductivity in LaNiSn has been found below the transition temperature Tc=0.59 K by measurements of the electrical resistivity and the a.c. magnetic susceptibility on a single-crystalline sample. The upper critical magnetic field was determined by the field dependence of the transition temperature. The non-saturating behavior in the magnetoresistance for transverse configurations suggests that LaNiSn is a compensated metal with no open orbits along the principal axes of the orthorhombic structure.

The first-order valence transition in has been investigated for single crystalline samples with x = 0.32 and x = 0.35 as well as for polycrystalline samples with (x varied in steps of 0.01) through the measurements of magnetic susceptibility, . For the single crystal with x = 0.32, exhibits a strong anisotropic mixed-valence behaviour. On the other hand, of the crystal with x = 0.35 exhibits a sharp first-order valence transition at 50 K. In both crystals, the strong anisotropy, , is maintained as in the host compound CeNiSn. The arc-melted polycrystalline alloys with a narrow range of Co composition, x = 0.33-0.37, show a sharp drop in below 70 K and large hysteresis. This transition becomes sharper by annealing at . For the optimum concentration x = 0.35, the drop in at the transition becomes as high as 72% for the single crystal and 69% for the polycrystalline alloy for which a jump in ac heat capacity was observed at 55 K. Analysis of the above results reveals that the phase transition involves a large change in the Kondo temperature . The small volume discontinuity at the transition suggests that the phase transition is not due to a Kondo volume collapse. A possible mechanism responsible for the phase transition in the present alloys is proposed.

Kondo semiconductors are a class of strongly correlated f-electron materials whose low-energy excitations exhibit a (pseudo)gap at low temperatures. The significant difference between the pseudogap in orthorhombic CeNiSn and CeRhSb and the real gap in cubic Ce 3 Bi 4 Pt 3 and YbB 12 is highlighted by a comparison of transport properties. Low-temparature measurements of the magnetoresistance, Hall coefficient and specific heat of CeNiSn have revealed a field-induced excitation of the coherent low-carrier state. A systematic study of CeNi 1− x T x Sn ( T = Co, Cu and Pt ) has shown that the residual carriers in CeNiSn are immobilized by 1% substitution irrespective of the substitutes. Further substitution with 5% Cu induces a magnetic instability at T = 0.

We grew Bi 2 Sr 2 CaCu 2 O y (Bi-2212) single crystals by the modified vertical Bridgman (VB) method, and investigated their characteristics in order to clarify the optimum growth conditions for obtaining high-quality Bi-2212 single crystals. The Bi-2212 single crystals were grown changing pulling rates or using starting materials after pre-treatments. We found that the superconducting critical temperature ( T c ) of the single crystal prepared at a slow growth rate of 0.25 mm/h was about 88 K and that the single crystals were a Bi-2212 single phase. Moreover, the single crystals grown using the starting materials pre-treated in Ar and O 2 atmospheres, had the T c of about 88 and 86 K, respectively. In addition, both of single crystals were Bi-2212 single phase.

We present thermal-conductivity $\ensuremath{\kappa}$ and thermopower S measurements on high-quality single crystalline CeNiSn along the three crystallographic axes $a, b,$ and c in the temperature range between 100 mK and 7 K and in magnetic fields up to 8 T applied along the a axis. Both $\ensuremath{\kappa}$ and S are highly anisotropic. However, characteristic features that may be attributed to the opening of a pseudogap in the electronic density of states (DOS) at the Fermi energy $\ensuremath{\eta}$ below 10 K are seen for all three crystallographic directions. These features are strongly suppressed by a magnetic field of 8 T applied along the a axis. At the lowest temperatures we have evidence for the presence of a residual metallic DOS at $\ensuremath{\eta},$ again for all three directions. The saturation of the reduced Lorenz number ${L/L}_{0}$ to a value distinctly higher than one is an interesting feature which deserves further investigation.

We report on measurements of the specific heat C and magnetization M of CeNi1−xCuxSn single crystals for T K . For x=0.05 an increase of C/T and M (measured in a magnetic field B=0.1 T applied parallel to the a-direction) towards low T down to 0.1 K indicates absence of magnetic order while for x=0.078 a maximum in M is found at T M ∼0.39 K . The magnetization M(B) for both crystals measured at 0.3 K along the a-direction increases linearly up to 7 T without any indication of saturation except for a small superimposed Brillouin-like feature. The critical concentration for the onset of magnetic order is estimated to xc=0.065.

The magnetic susceptibility χ=M/B for single crystals CeNiSn and CeRhSb have been measured at various magnetic fields up to 14 T as a function of temperature from 3.8 to 50 K. With increasing field B||a from 5 to 14 T, the maximum in χa(T) at 13 K for CeNiSn is gradually smeared, whereas that for CeRhSb remains at 20 K. These field dependencies are well reproduced by assuming a Zeeman splitting of the pseudogapped density of states with gJ|Jz|=1.15 and 0.9, respectively, for CeNiSn and CeRhSb.

URhGe crystallizes in the orthorhombic TiNiSi-type of structure and has been studied untill now only in polycrystalline form. Here, we report on the low-temperature specific heat of URhGe measured on a single crystal. The compound orders ferromagnetically at T C =9.6 K. Because of this low magnetic-ordering temperature, the specific heat c p cannot be described by the usual expression γT + aT 3 , also at low temperatures. Up to 7 K, c p is satisfactorily described by the relationship γT + bT 2 , which must be associated with the temperature depenedence of the magnetization in this temperature interval. The value of γ amounts to 164 mJ/mol U K 2 . We have also studied the effect on c p of an external magnetic field applied along the principal axes. The results are discussed in terms of the strong magnetic anisotropy of URhGe.

This paper presents a class D series resonant inverter with a series capacitor and an auxiliary switch. A capacitor and a switch connected in parallel are added to the series resonant circuit in series, which regulates the output power without frequency modulation. The entire impedance is changed by the difference between the switching frequency and the two resonant frequencies. While the auxiliary switch is on, the switching frequency is equal to the resonant frequency of a series circuit composed of a resistor R, an inductor L and a capacitor C. While the auxiliary switch is off, the switching frequency is equal to the resonant frequency of a series circuit composed of R, L, C and an additional capacitor. Applying the sub-optimum class E switching condition to the auxiliary switch, high power conversion efficiency is maintained. State equations are solved with MATLAB for each state. The calculated waveforms were agreed with the simulation results and experiment results. The maximum measured power conversion efficiency was 90.2% at 200 kHz.

We present a detailed study of the field (B) - temperature (T) phase diagram of the heavy-fermion antiferromagnet ${\mathrm{Ce}}_{7}{\mathrm{Ni}}_{3}$ that crystallizes in the hexagonal ${\mathrm{Th}}_{7}{\mathrm{Fe}}_{3}$-type structure with three nonequivalent Ce sites $(\mathrm{Ce}{}_{\mathrm{I}},$ $\mathrm{Ce}{}_{\mathrm{II}},$ and $\mathrm{Ce}{}_{\mathrm{III}}).$ This compound undergoes two magnetic transitions at ${T}_{N1}=1.9\mathrm{K}$ and ${T}_{N2}=0.7\mathrm{K}$ in zero field. Below ${T}_{N1},$ an incommensurate spin density wave (SDW) develops, and below ${T}_{N2}$ a commensurate SDW appears independently. By applying fields along the c axis, both ${T}_{N1}$ and ${T}_{N2},$ are suppressed and vanish at 0.3 T. For $B\ensuremath{\Vert}cg0.7\mathrm{T},$ however, another magnetic phase appears below 0.5 K, which was found by magnetoresistance, specific heat, and magnetization measurements. The separation of the field induced phase from the SDW phase is attributed to large spin fluctuations of $\mathrm{Ce}{}_{\mathrm{III}},$ which originate from a geometrical frustration in the quasiregular tetrahedron made of $\mathrm{Ce}{}_{\mathrm{I}}$ and $\mathrm{Ce}{}_{\mathrm{III}}.$

We have measured the thermal conductivity of isostructural compounds CePtSn, CeNiSn, CeRhSb, and CeRhAs with the orthorhombic e-TiNiSi-type structure. It is found that the phonon thermal conductivity is reduced in a systematic way with increasing Kondo temperature T K . The scattering of phonons by valence fluctuations should play a dominant role in such a reduction. The gap formation in the electronic density of states enhances the phonon thermal conductivity significantly in CeRhAs with a gap width of 280 K, while it is weak in CeNiSn or CeRhSb with a pseudogap of 20-30 K. A phenomenological model is proposed for the unusual temperature dependence of phonon thermal conductivity by taking account of the strong dependence of the electron-phonon scattering rate on both T K and the energy gap.

K. Proke$ s*, T. Tahara, Y. Echizen, T. Takabatake, T. Fujita, I.H. Hagmusa, J.C.P. Klaasse E. Br . uck, F.R. de Boer, M. Divi$ s, V. Sechovsk$ y Hahn-Meitner-Institute, SF-2, Glienickerstrasse 100, Berlin D-141 09, Germany Department of Quantum Matter, ADSM, Hiroshima University, Higashi, Hiroshima 739-8526, Japan Van der Waals–Zeeman Institute, University of Amsterdam, 1018 XE, Amsterdam, The Netherlands Department of Electronic Structures, Charles University, 12116 Prague 2, Czech Republic

We report on the resistivity in CeNiSn at temperatures down to 0.035 K and in magnetic fields up to 20 T . The resistivity as a function of temperature T exhibits T2 dependence with a huge coefficient. Clear Shubnikov-de Haas (SdH) oscillations are observed for the two samples where the electrical current is applied along the b-axis, while possible traces of SdH oscillations are noticed for the other two samples where the current is applied along the a and c axes, respectively.

The resistivity ρ, magnetic susceptibility χ, and specific heat C were measured for a single crystal of the valence-fluctuating hexagonal system CeRhSn. Strong anisotropy in both the resistivity (ρa>ρc) and magnetic susceptibility (χc>χa) was found. A hump appears in ρc(T) below 7 K , where both C/T and χ exhibit strong upturns. Power-law behaviors χc∝T−1.1 and χa∝T−0.35 were found below 4 and 16 K , respectively, down to 0.4 K . These results suggest the presence of unquenched moments in the quasi-Kagome lattice.

The thermopower S; electrical resistivity r; and magnetic susceptibility w are reported on CeRh1� xMxSn (M ¼ Co; Ni, Ru; xp0:25). The Ni doping changes the valence-fluctuating behavior of wðTÞ for x ¼ 0 to the Currie–Weiss type, whereas the Ru one to the Pauli-type. Nevertheless, all the substitutions result in a decrease of the rather large maximum of S ¼ 60 mV=K for x =0 . r 2003 Elsevier Science B.V. All rights reserved.

Magnetoresistance measurements have been performed on CeNiSn at low temperatures down to 35 mK and in magnetic fields up to 20 T. Shubnikov-de Haas oscillations, observed for the first time, provide clear evidence that CeNiSn, formerly called a Kondo semiconductor, is a metal. The frequency and associated effective mass are 65 T and 13me for the field direction parallel to the crystallographic c-axis.

The temperature dependence of the electronic states of Kondo semimetal CeNiSn has been studied by high-resolution photoemission spectroscopy. The results have been compared with those of LaNiSn. The temperature-dependent spectral weight reduction of CeNiSn is observed below 30 K at binding energies between ∼20 meV and EF, and is similar to that of the Kondo insulator Ce3Bi4Pt3. This behavior is not observed for LaNiSn. The spectral intensity of Ce 4f derived state near the Fermi level (EF) is enhanced at temperatures above a characteristic temperature, but the spectral intensity at EF is reduced at 7 K.

The phase transition in the ternary uranium compound UCu2Sn is studied by using muon spin relaxation method (μSR). Previous measurements of magnetic susceptibility and specific heat showed a pronounced anomaly at 16 K, suggesting an antiferromagnetic order. However, no significant change in the μSR spectra has been observed which indicates the absence of the antiferromagnetic phase transition at 16 K. We also found the fast μSR below 10 K, probably due to a magnetic ordering.

Thermoelectric-power (TEP) measurements are reported on CeNi1−xTxSn (T=Co, Cu, Pt) and Ce1−yLayNiSn for x, y =0.01 and 0.05. The sharp maximum at 3 K in the TEP for pure CeNiSn disappears for x or y=0.01. The local maximum at 20 K is enhanced by Co and La substitutions for x or y=0.05, whereas it is suppressed by Cu substitution. The results suggest that the substitutions of Co and La dope holes into the renormalized band with a pseudogap and substitution of Cu with an additional 3d electron enhance the antiferromagnetic correlations.

Electrical resistivity ρ , Hall coefficient R H and magnetic susceptibility χ , are reported on single crystals of Ce 1− y La y NiSn ( y =0, 0.01 and 0.05). The negative increase in R H for y =0 on cooling below 4 K is weakened for y =0.01, whereas R H for y =0.05 remains positive down to 1.4 K. At this temperature, both ρ b and ρ c for y =0.01 are about five times larger than that for y =0, while those for y =0.05 saturate to values smaller than those for y =0.01. Furthermore, the maximum in χ a at 13 K disappears for y =0.05. The close resemblance of these results to those found in CeNi 1− x Co x Sn indicates that irrespective of the 4f-site and the non-4f site the Kondo-hole imputity strongly scatters the carriers remaining in the pseudogap.

Electrical resistivity, magnetic susceptibility and Hall effect were measured on a hexagonal antiferromagnet UCu 2 Sn. Below T N = 16K, the resistivity ρ sharply increases along all the a -, b - and c -axis. The anisotropic behavior, ρ b > ρ a > ρ c , suggests that the magnetic superzone gap is larger in the c -plane than along the c -axis. However, anisotropy in the magnetization for H‖a and H‖c is weak even in the antiferromagnetically ordered state. The magnetization curve of a powdered sample exhibits a spin-flop like behavior at 230 kOe.

Magnetic, transport, thermal, and crystallographic properties are reported for single crystals of CeRhSn crystallizing in the hexagonal ZrNiAl-type structure. We found high anisotropy in both electrical resistivity (r a’5r c at 70 K! and magnetic susceptibility ( x c’10x a at 0.4 K!, which is atypical for a valence-fluctuating Ce compound. At low temperatures, r(T) and x(T) show power-law behaviors; r a(T)}T 1.5 and r c(T)}T, and x a}T 20.35 and x c}T 21.1 down to 0.4 K. These behaviors and the rather large residual resistivity were not affected by long-term annealing. On cooling fro m7Kt o 0.5 K, thespecific heat divided by temperature C/T increased as 2ln T and saturated to a rather large value of 0.2 J/mol K 2 . These experimental results are discussed in relation to the possible atomic disorder.

The effect of doping in CeNiSn has been studied by the measurements of electrical resistivity, Hall coefficient and magnetic susceptibility for single crystals of ${\mathrm{CeNi}}_{1\ensuremath{-}x}{T}_{x}\mathrm{Sn}$ $(T=\mathrm{Co},$ Cu, and Pt) and ${\mathrm{Ce}}_{1\ensuremath{-}y}{\mathrm{La}}_{y}\mathrm{NiSn}$ $(x,y=0.01$ and 0.05). All these impurities are found to increase the residual resistivity by several times up to 1 m\ensuremath{\Omega} cm for x or $y=0.01,$ while for x or $y=0.05$ the resistivities along the orthorhombic b and c axes saturate to values smaller than those for 0.01. Furthermore, the low-temperature increase in the Hall mobility of CeNiSn was found to be strongly suppressed in a similar way by all the impurities. These results indicate that residual carriers in CeNiSn with an anisotropic gap are immobilized by any impurity substituted either in the $4f$ site or the non-$4f$ site.

Among rare-earth-based compounds showing the Kondo effect, systems exhibiting a small energy gap in the heavy-electron band are referred to as Kondo semiconductors. We have measured thermoelectric properties of CeNiSn, CeRhSb, CeRhAs, YbB/sub 12/ and their substituted alloys. The thermopower of CeRhAs has a positive maximum of 130 /spl mu/V/K at 40 K, while that of YbB/sub 12/ has a negative peak of -150 /spl mu/V/K at 10 K. For both CeNiSn and CeRhSb, the electrical resistivity is less than 200 /spl mu//spl Omega/cm and the thermal conductivity is about 50 mW/Kcm at 60 K. The figure of merit Z for CeRhAs and CeRhSb has the maximum value of 1.0/spl times/10/sup -3//K at 125 K and 2.2/spl times/10/sup -3//K at 13 K, respectively. Therefore, these compounds have high potential for a novel thermoelectric cooling material at low temperatures.