First-principles Calculation Combined With Thermodynamic Analysis Of Ir-based Active Oxide System

The structures and properties of rutile (IrxTi1-x)O2 solid solutions and rutile+fluorite (IrxZr1-x)O2 solid solutions have been studied and discussed in the present study by a combination of DFT method and thermodynamic theory model. The structure parameters, total energies of rutile (IrxTi1-x)O2 solid solutions and rutile+fluorite (IrxZr1-x)O2 solid solutions were investigated by optimizing structures based on density functional theory (DFT) calculations. Thermodynamic stability was researched and the Spinodal and Binodal curves were plotted based on thermodynamic theory. The results indicated that:1. The relative error value is small compared to the calculated lattice constants and unit cell volume of rutile IrO2, TiO2 and fluorite ZrO2 with the date in JCPDS cards.2. The structure of rutile (IrxTi1-x)O2 is related to the composition x:Lattice constant a monotonically decreases with composition x, c monotonically increases with composition x, the volume of the system monotonically increases with the composition x, total energy monotonically increases with composition x. Both lattice constant a and c monotonically decrease with composition x, the volume of the system monotonically decreases and total energy monotonically increases with composition x for rutile and fluorite (IrxZr1-x)O2.3. The calculated Spinodal and Binodal curves of fluorite (IrxTi1-x)O2 indicated that, IrO2-TiO2 has no solid solution phenomenon when temperature is below 1200K using T-independent method, and the critical temperature of IrO2-TiO2 is 4144K, which does not match the results with other literature. The calculated Spinodal and Binodal curves are more reasonable by using exponential T-dependent and linearly T-dependent.4. The calculated Spinodal and Binodal curves of fluorite (IrxZr1-x)O2 indicated that, IrO2-ZrO2 has no solid solution phenomenon when temperature is below 3000K using T-independent method, and the critical temperature of IrO2-ZrO2 is 9667K, which does not match the results with other literature. The calculated Spinodal and Binodal curves are more reasonable by using exponential T-dependent and linearly T-dependent and have a certain solid solution when temperature is 1100K using exponential T-dependent. The fluorite Ir0.64Zr0.36O2 have a reasonable critical point (2459K).5. The total energy of rutile and fluorite (IrxZr1-x)O2 solution is larger than the total energy of mechanical mixture of IrO2 and ZrO2. which indicated that Spinodal decomposition may occur; according to the rutile, fluorite (IrxZr1-x)O2 solid solution, and we got the Binodal and Spinodal curves and plotted the equilibrium phase diagram of Ir-Zr-O.The present fundamental study of (IrxTi1-x)O2, (IrxZr1-x)O2 provides a guideline for the phase and microstructure design of Ir-based mixed oxides, has a very important guiding significance.