Compositional control of tunnel features in hollandite-based ceramics: structure and stability of (Ba,Cs)1.33(Zn,Ti)8O16

The effect of cesium content on the thermodynamic stability and chemical durability of (Ba,Cs)1.33(Al,Ti)8O16 hollandite

“…A phase assemblage containing BaTiO 3 perovskite is likely to form in synthetic rock (Synroc) systems, so the issue of stability can be addressed directly by thermodynamics. Equations and were used to demonstrate a widely utilized method for using the enthalpies of reaction (Δ H rxn ) at standard conditions to assess phase stability 4‐7,12 . where Δ H f,ox (H5) was given in Table 2 and Δ H f,ox (BaTiO3) = −152.3 ± 4.0 kJ/mol 44 .…”

“…Elemental concentrations in leaching solution were measured by ICP‐MS and inductively coupled plasma‐atomic emission spectroscopy (ICP‐AES). Details about instrument and experimental procedure can be found by prior studies 6,7,12 …”

“…Equations 4 and 5 were used to demonstrate a widely utilized method for using the enthalpies of reaction (ΔH rxn ) at standard conditions to assess phase stability. [4][5][6][7]12 where ΔH f,ox (H5) was given in Table 2 and ΔH f,ox (BaTiO3) = −152.3 ± 4.0 kJ/mol. 44 Thus, ΔH rxn values of H1-H5 can be calculated and listed in Table 2.…”

“…These analyses further convince the trend that more Cs content stabilizes the Alsubstituted hollandite itself, which has been observed in Ga-, Zn-and Fe-substituted hollandites. 6,7,12 In addition, the relatively low Cs-containing samples are more likely to decompose and form soluble Cs-containing phases, which would further affect chemical durability of Al-substituted hollandite in aqueous solution.…”

“…Titanate‐based hollandite has been considered as one of the most promising host matrices for Cs immobilization due to its structural 3 and thermodynamic stability 4‐7 as well as its chemical durability 8‐10 . These hollandites are described by the general formula (Ba x 2+ Cs y + )(M,Ti 4+ ) 8 O 16 (0 < x + y < 2), where M is a trivalent or divalent cation (M = Al 3+ , Ga 3+ , Fe 3+ , Zn 2+ , Mg 2+ , etc) 4‐7,11,12 . In a unit cell, the hollandite structure consists of eight (M,Ti)O 6 octahedra which are linked by corners and edges to form tunnels.…”