| Computational materials and materials design combined with computer techniques are important contents in materials science research. The structures and properties of rutile-type and anatase-type RuO2, TiO2 and (Ru1-x,Tix)O2 solid solutions have been researched and discussed in the present study using DFT method combined with thermodynamic model. The structure parameters, ground energies and formation energies of rutile-type and anatase-type RuO2, TiO2 and (Ru1-xTix)O2 solid solutions are investigated by optimizting the crystal structures using plane-wave pseudopotential method within density functional theory (DFT). Thermodynamic stability is researched and the miscibility gap curves are plotted based on thermodynamic model. Several powder samples are prepared by sol-gel method. cla-x is used to determine the composition of the phases, the DFT calculations are verified by experiments. Results indicated that:1. The relative error value is small by compared the calculated lattice constants and unit cell volume of rutile-type and anatase-type RuO2 and TiO2 with the JCPDS cards.2. Lattice constant a increases but c decreases monotonously with the fraction of TiO2 for rutile (Ru1-x,Tix)O2。c/α decreases monotonously with increasing the fraction of TiO2, which can be used to determine the compositon. Volumes Vo decreases monotonously with the fraction of TiO2 for anatase (Ru1-x,Tix)O2. Total energy E0 decreases monotonously with the fraction of TiO2 for both rutile and anatase (Ru1-x,Tix)O2. The total energy E0 large than the total energies of mechanical mixture of RuO2 and TiO2 indicated that spinodal decomposition may occur in rutile and anatase (Ru1-x,Tix)O2 system.3. The calculated BN curve by the T-independent method for rutile and anatase (Ru1-x,Tix)O2 showed that no solid solution observed when temperature<1500 K, which is contradictory to the previous and present experiment results. The BN and SN curves obtained by Empirical T-dependent method showed that the selection of Q at melting point or decomposition temperature distinctly affect the prediction of the miscibility gap for rutile and anatase(Ru1-x,Tix)O2.4. The viewpoint of Connolly and Williams is introduced and the Modified T-dependent method is established. The calculated BN curve for rutile and anatase (Ru1-x,Tix)O2 solid solution indicated that solid solubility of TiO2 in RuO2 large than that of RuO2 in TiO2 at any temperature. This phenomenon is confirmed by the available literatures and present study, from this point we can confirm that the calculated BN curve by the Modified T-dependent method is more credible. Meanwhile, the calculated BN curve by the Modified T-dependent method explained the reason why (Ru1-x,Tix)O2 solid solution can be obtained at the regular prepared temperatures. |
