  First-principles calculation and anharmonic dynamical theory were used in
sequence to explain a large excess heat capacity observed in yttria-stabilized
zirconia in comparison with the additive rule value.
  It is found that the excessive shape of heat capacity decays gradually with
the Y$_{2}$O$_{3}$ doping when the number of environmentally different O sites
falls to its zero value at 33 mol % Y$_{2}$O$_{3}$-ZrO$_2$ due to the Y atoms
adjacent.
  The model and results presented in this work provide a key insight into the
complex behaviour and characterization of fast-ion conductors.
