X-ray study with synchrotron radiation for filled skutterudite YbFe4P12 at ambient and high pressures

By use of synchrotron radiation, X-ray diffraction of filled skutterudite YbFe4P12 has been studied at ambient and high pressures. The crystal structure of this compound was refined by the Rietveld analysis of powder X-ray diffraction data at ambient pressure. The positional parameters, bond distances and bond angles are obtained for YbFe4P12. The distance between Yb and P atoms in YbFe4P12 is 2.973 Å, and almost agrees with the sum of the atomic radius (1.92 Å) of Yb and the covalent radius (1.06 Å) of P. Powder X-ray diffraction patterns of this phosphide were measured with a diamond-anvil cell and an imaging plate at room temperature and high pressures. The volume (V) vs. pressure (P) curve for YbFe4P12 is also fitted by the Birch equation of state. Bulk modulus (B0) and its pressure derivative (B0′) are 167±6 GPa and 2±1, respectively. The cell volume of YbFe4P12 decreased monotonically with increasing pressure up to 10 GPa. The V–P curve for YbFe4P12 suggests that the valence state in Yb ions does not change at high pressures. The electrical resistivity of the good sample of YbFe4P12 prepared at high pressure was measured at low temperatures. The resistivity minimum is observed at around 50 K. The physical properties of YbFe4P12 with a 4f-hole are compared to those of CeFe4P12 with a 4f-electron.