Elsevier

Physica B: Condensed Matter

Volumes 230–232, February 1997, Pages 698-701
Physica B: Condensed Matter

Systematic study in mixed valence system Yb4(As1−xSbx)3

https://doi.org/10.1016/S0921-4526(96)00808-3Get rights and content

Abstract

In Yb pnictides with anti-Th3p4 structure, the valence of Yb decreases from about 2.25 in Yb4As3 to about 2 in Yb4Bi3 with increasing weight of pnictogen. In Yb4As3, charge ordering around 300 K is observed and in the charge ordered phase heavy fermion behavior is seen in spite of extremely low carrier concentration. On the other hand, Yb4Sb3 is a valence fluctuating system. So, to make systematic studies from Yb4As3 to Yb4Sb3 we grew single crystals of Yb4(As1−xSbx)3. With increasing Sb content, the absolute value of the resistivity decreases due to the increase of the number of carriers and the charge ordering temperature decreases reflecting the increase of the screening effect, and at 29% charge ordering seems to disappear. The γ-value, however, is still large even in Sb 29% sample. The large γ-value of Yb4(As1−xSbx)3 is considered to be independent ofthe carrier concentration.

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    Although such models may not be literally true due to the three-dimensionality of the electronic states, they describe the important aspect that a strain coupling to the degenerate band states may easily lead to distortions of the cubic structure and simultaneous repopulation among the 4f states of Yb4As3. Thermal and transport measurements on P- and Sb-doped samples gave further experimental evidence for the scenario described here [7,12,30] (Fig. 6): With increasing concentration x of phosphorus, the electrical resistivity of Yb4(As1−xPx)3 grows drastically, and with x=0.3 it is nearly insulating, while the specific heat and the magnetic susceptibility are almost the same as those of pure Yb4As3. With increasing Sb content x, the absolute value of the resistivity of Yb4(As1−xSbx)3 decreases due to the increase of the number of charge carriers and the system becomes more metallic while again the specific-heat γ value is roughly the same as in the pure compound and thus almost independent of the carrier concentration.

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