Experimental X-ray powder diffraction patterns and refined unit cell parameters for two barium hollandite-type compounds, BaxFe2xTi8−2xO16, with x=1.143 and 1.333, are reported here. Compared to the tetragonal parent structure, both compounds exhibit monoclinic distortions that increase with Ba content [Ba1.333Fe2.666Ti5.334O16: a=10.2328(8), b=2.9777(4), c=9.899(1) Å, β=91.04(1)°, V=301.58(5) Å3, Z=1, ρcalc=4.64 g/cc; Ba1.143Fe2.286Ti5.714O16: a=10.1066(6), b=2.9690(3), c=10.064(2) Å, β=90.077(6)°, V=301.98(4) Å3, Z=1, ρcalc=4.48 g/cc]. The X-ray powder patterns for both phases contain a number of broad, weak superlattice peaks attributed to ordering of the Ba2+ ions within the tunnels of the hollandite framework structure. According to the criteria developed by Cheary and Squadrito [Acta Crystallogr. B 45, 205 (1989)], the observed positions of the (0k1)/(1k0) superlattice peaks are consistent with the nominal x-values of both compounds, and the k values calculated from the corresponding d-spacings suggest that the Ba ordering within the tunnels is commensurate for x=1.333 and incommensurate for x=1.143. High-temperature X-ray diffraction data indicate that the x=1.333 compound undergoes a monoclinic→tetragonal phase transition between 310 and 360 °C.
Equilibria Equilibria E 4000 Subsolidus Phase Equilibria and Crystal Chemistry in the System BaO-TiO 2 -Ta 2 O 5 . -Several new compounds exist in the title system, including four members of the orthorhombic (space group Cmcm) "rutile-slab" homologous series, BaTinTa4O11+2n (n = 3, 5, 7, 9). Three ternary phases with close-packed [Ba,O] layer structures related to that of 6L Ba4Ti13O30 are observed: 13L Ba18Ti53Ta2O129, 7L Ba 10 Ti 27 Ta 2 O 69 , and 8L Ba 6 Ti 14 Ta 2 O 39 . As revealed by single crystal XRD the 13L and 7L phases crystallize in the space group C2/m with Z = 2. Phases with tetragonal tungsten bronze related structures occur over large compositional ranges in the title system. -(VANDERAH*, T. A.; ROTH, R. S.; SIEGRIST, T.; FEBO, W.; LOEZOS, J. M.; WONG-NG, W.; Solid State
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