use of other compositions additionally the hafnia or gadolinia can be partially substituted with yttria zirconia other rare earth oxides such as lanthana ceria praseodymia neodymia promethia samaria europia terbia dysprosia holmia erbia thulia ytterbia and lutetia and also yttria calcia and magnesia up to about 20 25 mol and preferably only up to about 15 mol 0032 fig3 shows calculated thermal conductivity values for gadolinia hafhia compared to the thermal conductivity of yttria zirconia u201c current tbc u201d as a function of temperature to illustrate the benefit the reduction in thermal conductivity allows the coating thickness to be reduced by a corresponding amount while maintaining the same degree of thermal insulation decreasing the coating mass for use with a typical turbine blade will lower the blade pull at the blade root significantly at typical operating conditions which results in a significant increase in blade life and permits a reduction in mass of the disk to which the blades are attached the shafts to which the disks are attached etc if the thermal barrier coating were held at the same thickness and the cooling air flow held constant the substrate temperature would be reduced giving increased substrate creep life keeping the coating thickness constant and reducing the cooling airflow would increase engine efficiency combinations of these benefits e g slightly reduced.