  We reported the realization of a $^{174}\mathrm{Yb}^+$-$^{113}\mathrm{Cd}^+$
bi-species Coulomb crystal comprising $^{174}\mathrm{Yb}^+$ ions as coolant and
verified its potential for application as a $^{113}\mathrm{Cd}^+$ microwave
frequency standard employing sympathetic cooling.The two species of massive
ions stably trapped in a Paul trap make up this large two-component crystal.
The $^{113}\mathrm{Cd}^+$ ions are trapped in the center, which reduces
considerably RF heating and excess micromotion to which the
$^{113}\mathrm{Cd}^+$ ions are subjected. Under this scheme, the uncertainty
due to the second-order Doppler effect is reduced to $5\times10^{-16}$, which
represents an order of magnitude improvement over sympathetic cooled
$^{40}\mathrm{Ca}^+$-$^{113}\mathrm{Cd}^+$ crystal. The uncertainty from the
second-order Zeeman effect, which contributes the largest uncertainty to the
microwave-ion frequency standard, is reduced to $4\times10^{-16}$. The relevant
AC Stark shift uncertainty is estimated to be $4\times10^{-19}$. These results
indicate using $^{174}\mathrm{Yb}^+$ as coolant ions for $^{113}\mathrm{Cd}^+$
is far superior and confirm the feasibility of a sympathetic-cooled cadmium-ion
microwave clock system employing a $^{174}\mathrm{Yb}^+$-$^{113}\mathrm{Cd}^+$
two-component crystal.

Atomic Physics;Quantum Physics