Refinement of the structure of hydrogen–vacancy complexes in titanium by the Rietveld method

The VT1-0 titanium alloy (phase $\alpha$-Ti) with various hydrogen and hydrogen-vacancy concentrations has been studied. The stability of the 32-atom Ti–$nV$–$m$H supercell ($n$ is the number of the $V$ vacancies, and $m$ is the number of hydrogen atoms H) with varying numbers of vacancies and hydrogen atoms has been calculated from the first principles. The structural state of the $\alpha$-Ti phase has been identified by the Rietveld method based on the calculations of the supercell stability and the data on the defect concentration obtained using positron spectroscopy. The complete structural information on the considered states of the $\alpha$-Ti phase (the lattice parameters, spatial distribution of titanium and hydrogen atoms and vacancies) has been obtained.