Vibrational Spectroscopic Study of the System ALPHA-Co2SiO4–ALPHA-Ni2SiO4

The structure of the cation-deficient Ba4.0(1)Ce0.98(3)Nb10O30 barium cerium reduced niobate with a tetragonal tungsten bronze (TTB) type structure was refined from X-ray single crystal data (tetragonal, a=12.508(2) ?, c=3.9328(4) ?, S. G. P4/mbm, Z=1, R=0.019, Rw=0.023). It was found that rare earth substitution for Ba is accompanied by formation of vacancies in A sites. Vacancies were preferably formed in the A(1) cavities in the structure.