(Solved): What are valid reasons for adding Yttrium to the zirconia in the Thermal Barrier Coating (TBC) in ...

What are valid reasons for adding Yttrium to the zirconia in the Thermal Barrier Coating (TBC) in a turbine blade? Select one or more: a. To prevent a change of the crystallographic structure as the temperature changes b. To match the thermal conductivity of the TBC to the underlying oxide layer c. To match the thermal conductivity of the TBC to the metal substrate d. To avoid breakage during change in thermal conditions e. To increase the weight of the TBC