Barium hollandite-type compounds Ba_xFe_2xTi_8−2xO₁₆ with x=1.143 and 1.333

Abstract

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.

Preparation and characterization of (Ba,Cs)(M,Ti)8O16 (M=Al3+, Fe3+, Ga3+, Cr3+, Sc3+, Mg2+) hollandite ceramics developed for radioactive cesium immobilization

“…It is interesting to notice that literature indicated that the iron (Ba,Fe)-hollandite Ba 1.14 (Fe 2.28 Ti 5.71 )O 16 , i.e. a composition very close to the one studied in the present work, was monoclinic (a = 10.107 Å , b = 2.969 Å , c = 10.064 Å , b = 90.077°) [33]. However, in our case, the lines of the XRD pattern of Ba 1.16 Fe 2.32 Ti 5.68 O 16 sample (Fig.…”

Defects induced by electron irradiation in hollandite ceramics, specific radioactive cesium-host wasteforms: a 57Fe Mössbauer study

“…But, if the structure is monoclinic (I2/m space [8] hollandites which reported also one quadrupolar doublet at 300 K whose parameters were close to the ones of site 2. Moreover, few studies have reported a monoclinic structure for a close hollandite composition Ba 1.14 Fe 2.28 Ti 5.72 O 16 [9]. Therefore, we can wonder if our material does not display a slight monoclinic distortion not clearly detected by XRD and thus these two doublets (Figure 2a) would be related to the two different crystallographic sites.…”

Synthesis and characterization of the pseudo-hexagonal hollandites ALi2Ru6O12 (A=Na, K)

“…Hollandites have the formula A x B 8 O 16 and are typically tetragonal in symmetry [8]. Structurally, they consist of double chains of edgeshared transition metal BO 6 octahedra sharing corners to form large, four-sided tunnels along the c-axis in which alkali or alkaline earth cations reside.…”