The structural and the valence band electronic properties of bcc Ti-X alloys (X = V, Cr, Fe, Co, Nb, and Mo) were studied by first-principles calculations. To determine the effect of the concentration and atomic distribution of the alloying elements on the phase stability, ordered structure models and special quasirandom structure (SQS) models were used for emulating the solid solution state of the alloys. To clarify the phase stability of bcc Ti-X alloys with respect to a hexagonal close-packed (hcp) reference phase, the formation energy, structural parameters, and electronic properties were analyzed. Analysis of the formation energy showed that the hcp phase is more stable than the bcc phase when V, Cr, and Nb are added for all the calculated alloying element fractions x (0 ≤x≤0.50), whereas the bcc phase is stabilized when Fe, Co, are Mo are added. The dependence of the lattice constants on the alloying element was examined, and the calculations reproduced the experimental results well. The profile of the density of states in the solid solution changed continuously with the concentration of the alloying elements.
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