✍ Scribed by S.K. Dhar; K.A. Gschneidner Jr.; R. Vijayaraghavan
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YbNiSb has a cubic MgAgAs-type structure and the Yb ions are trivalent. The heat capacity, C, measured in the range 2-20 K is temperature-independent between 2 and 8 K (1.9 J/mol K 2) at zero field and shows magnetic field dependence. The value of C/T extrapolated to 0 K is 150 mJ/mol K 2. The resistivity (3.6 mlA cm at 300 K) decreases with temperature. These data indicate that YbNiSb is a possible low-carrier heavy-fermion compound.
A number of Yb-based equiatomic ternary compounds are known to have the cubic MgAgAs-type structure, e.g., YbNiSb, YbPtSb [1], YbPdBi, YbPtBi [2] and YbPdSb [3]. The cubic MgAgAs structure consists of three interpenetrating face-centered cubic arrays and the Yb ions occupy crystallographically equivalent sites in the lattice. Dhar et al. have reported the results of measurements of heat capacity (2-20 K) and magnetic susceptibility for YbPdSb and YbPdBi [4], both of which show marked deviations of the lattice constant from the value based on the lanthanide contraction. Effective paramagnetic moments of 4.39 and 4.04/~ and the Curie-Weiss temperature of -9K were obtained for the two compounds, respectively. It was found that C/T rises sharply at low temperatures and exceeds 1 J/mol K 2 at 2 K. The heat capacity, C, decreases monotonically with temperature down to 2K in YbPdBi, but in YbPdSb shows a small hump centered around 4.5 K. The values of C~ T extrapolated to 0 K, obtained from the C/T versus T 2 plot in the range 13-20K, for YbPdSb and YbPdBi were 240 and 470mJ/molK 2, respectively.
From these results, which did not rule out the occurrence of a phase transition below 2 K, it was inferred that both YbPdBi and YbPdSb are heavyelectron systems. Aliev et ai. [5] reported that the resistivity of both compounds showed maxima in the 50-100 K range and Fermi liquid behavior at helium temperatures, with values of 3.2 and 5 ~1~ cm/K 2 for the coefficient of the T 2 term of the resistivity. More recently, YbPtBi has been identified as a very heavy-
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