UC Davis

The high pressure properties of the novel tetrel-free clathrate, Ba₈Cu_13.1Zn_3.3P_29.6, were investigated using synchrotron powder X-ray diffraction. The pressure was applied using a diamond anvil cell. No structural transitions or decomposition were detected in the studied pressure range of 0.1-7 GPa. The calculated bulk modulus for Ba₈Cu_13.1Zn_3.3P_29.6 using a third-order Birch-Murnaghan equation of state is 65(6) GPa at 300 K. This bulk modulus is comparable to the bulk moduli of Ge- and Sn-based clathrates, like A₈Ga₁₆Ge₃₀ (A = Sr, Ba) and Sn_19.3Cu_4.7P₂₂I₈, but lower than those for the transition metal-containing silicon-based clathrates, Ba₈T_xSi_46-x, T = Ni, Cu; 3 ≤ x ≤ 5.