ISOTHERMAL SECTION AT 1600 degrees C FOR THE ZrO2-HfO2-Sm2O3 SYSTEM

According to the results of the samples studied by the method of X-ray phase and microstructural analyses, the phase equilibria in the ternary system ZrO2-HfO2-Sm(2)O(3)were investigated. The formation of new phases in the ZrO2-HfO2-Sm2O3 system at 1600 degrees C was not observed. It is established that in the studied system at 1600 degrees C fields of solid solutions on the basis of tetragonal (T) modification of ZrO2, monoclinic (M) modifications of HfO2 and monoclinic (B) modifications of Sm2O3, and also the ordered phase with structure of the pyrochlore-type (Py) Ln(2)Zr(2)O(7) (Ln(2)Hf(2)O(7)). The boundaries of the phase fields and the parameters of the unit cells of the formed phases are determined. The studied isothermal cross section of the ZrO2-HfO2-Sm2O3 system is characterized by the formation of continuous rows of cubic solid solutions based on a phase with a structure of the pyrochlore-type Sm2Zr2O7(Sm2Hf2O7) and a structure of the fluorite type F-ZrO2 (HfO2). It is established that two regions of homogeneity of cubic solid solutions (F) are formed in the investigated system. The existence of these regions of homogeneity is due to the rupture of the solubility of the F-ZrO2 (HfO2) phase in the region of the existence of an ordered phase with a structure of the pyrochlore-type Sm2Zr2O7 (Sm2Hf2O7). It is established that a solid solution based on a cubic modification with a fluorite-type structure exists in equilibrium with all phases observed in the system. Isothermal cross-section of the state diagram of the system ZrO2-HfO2-Sm2O3 at 1600 degrees C is characterized by the presence of one three-phase (F + T + M), as well as five two-phase (B + F, two - F + Py, M + F, T + F) areas.