Systematic study in mixed valence system Yb-4(As1-xSbx)(3)

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 Yb-4(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 gamma-value, however, is still large even in Sb 29% sample. The large gamma-value of Yb-4(As1-xSbx)(3) is considered to be independent of the carrier concentration.