Isothermal section of the ZrO2–HfO2–Nd2O3 ternary phase diagram at 1100 °C

Abstract

In the presented work, based on the results obtained by X-ray diffraction and microstructural analysis, phase equilibria have been studied and an isothermal section of the ZrO2–HfO2–Nd2O3 ternary phase diagram at 1100 °C has been constructed. Unit cell parameters were calculated by the least squares method using the LATTIC software. The International Powder Standards Committee database (JSPSDS International Center for Diffraction Data 1999) was used to determine the phase composition.It was found that in the studied system are formed regions of solid solutions based on a cubic fluorite-type (F) modification, a tetragonal (T) modification of ZrO2, a monoclinic (М) modification of HfO2, a hexagonal (А) modification of Nd2O3, as well as an ordered (Py) pyrochlore phase of Nd2Zr2O7 (Nd2Hf2O7). The boundaries of the phase regions and the unit cell parameters are determined. A continuous series of solid solutions based on the ordered pyrochlore (Py) phase of Nd2Zr2O7 (Nd2Hf2O7) at the studied temperature is derived. The unit cell parameters of the ordered pyrochlore (Py) phase vary from a = 1.0633 nm for the two-phase composition (Py + M), 47.5 mol% ZrO2 – 47.5 mol% HfO2 – 5 mol% Nd2O3) to a = 1.0639 nm for the boundary composition of the solid solution (37.5 mol% ZrO2 – 37.5 mol% HfO2 – 30 mol% Nd2O3) and then up to a = 1.0648 nm for the two-phase (Py + A) composition (30 mol% ZrO2 – 30 mol% HfO2 – 40 mol% Nd2O3) which located along the Nd2O3 – (45 mol% ZrO2 – 55 mol% HfO2) constant ratio line. The studied isothermal section is characterized by the formation of two three-phase (Py + F + M and F + T + M) and six two-phase (A + Py, Py + M, Py + F, F + M, T + M, F + T) regions. In the ZrO2–HfO2–Nd2O3 ternary system, no new phases are detected at the temperatures studied.