TY - JOUR
T1 - Compositional control of tunnel features in hollandite-based ceramics
T2 - structure and stability of (Ba,Cs)1.33(Zn,Ti)8O16
AU - Grote, R.
AU - Zhao, M.
AU - Shuller-Nickles, L.
AU - Amoroso, J.
AU - Gong, W.
AU - Lilova, K.
AU - Navrotsky, A.
AU - Tang, M.
AU - Brinkman, K. S.
N1 - Funding Information:
KSB and MZ acknowledge support of thermodynamic measurements as part of the Center for Hierarchical Waste Form Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0016574. LSN gratefully acknowledges financial support from the DOE-EPSCoR Project Number: DE-SC0012530, ‘‘Radionuclide Waste Disposal: Development of Multi-scale Experimental and Modeling Capabilities’’ for support of modeling. The calorimetric experiments carried out at University of California, Calorimetry at Davis were supported as part of the Materials Science of Actinides, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award Number DE-SC0001089. JA acknowledges the support of durability testing by the U.S. Department of Energy, Office of Nuclear Energy, Fuel Cycle Technology, Materials Recovery and Waste Form Development Campaign. Work conducted at Savannah River National Laboratory was supported by the U.S. Department of Energy under contract number DE-AC09-08SR22470.
Publisher Copyright:
© 2018, Springer Science+Business Media, LLC, part of Springer Nature.
PY - 2019/1/1
Y1 - 2019/1/1
N2 - The impact of composition on the tunnel features of hollandite materials for the purpose of radioactive cesium (Cs) immobilization was evaluated. The barium (Ba) to cesium (Cs) ratio was varied in the tunnel sites referred to as the A-site of the hollandite structure. Zinc (Zn) was substituted for titanium (Ti) on the B-site to achieve the targeted stoichiometry with a general formula of BaxCsyZnx+y/2Ti8−x−y/2O16 (0 < x < 1.33; 0 < y <1.33). The tunnel cross-section depended on the average A-site cation radius, while the tunnel length depended on the average B-site cation radius. Substitution of Cs resulted in a phase transition from a monoclinic to a tetragonal structure and an increase in unit cell volume of 1.8% across the compositional range. Cs loss due to thermal evaporation was found to decrease in compositions with higher Cs content. The enthalpies of formation from binary oxides of Zn-doped hollandite measured using high-temperature oxide melt solution calorimetry were strongly negative, indicating thermodynamic stability with respect to their parent oxides. The formation enthalpies became more negative, indicating hollandite formation is more energetically favorable, when Cs was substituted for Ba across the range of Zn-doped compositions investigated in this study. Compositions with high Cs content exhibited lower melting points of approximately 80 °C. In addition, high Cs content materials exhibited a significant reduction in Cs release from the solid to liquid phase by leaching or aqueous corrosion as compared to low Cs content materials. These property changes would be beneficial for applications in radioactive cesium immobilization in a multi-phase ceramic by allowing for decreased processing temperatures and higher cesium weight loadings. More broadly, these results establish the link between composition, structural symmetry, and thermodynamic stability for tunnel structured ceramics with implications in the design of new energy conversion and storage materials.
AB - The impact of composition on the tunnel features of hollandite materials for the purpose of radioactive cesium (Cs) immobilization was evaluated. The barium (Ba) to cesium (Cs) ratio was varied in the tunnel sites referred to as the A-site of the hollandite structure. Zinc (Zn) was substituted for titanium (Ti) on the B-site to achieve the targeted stoichiometry with a general formula of BaxCsyZnx+y/2Ti8−x−y/2O16 (0 < x < 1.33; 0 < y <1.33). The tunnel cross-section depended on the average A-site cation radius, while the tunnel length depended on the average B-site cation radius. Substitution of Cs resulted in a phase transition from a monoclinic to a tetragonal structure and an increase in unit cell volume of 1.8% across the compositional range. Cs loss due to thermal evaporation was found to decrease in compositions with higher Cs content. The enthalpies of formation from binary oxides of Zn-doped hollandite measured using high-temperature oxide melt solution calorimetry were strongly negative, indicating thermodynamic stability with respect to their parent oxides. The formation enthalpies became more negative, indicating hollandite formation is more energetically favorable, when Cs was substituted for Ba across the range of Zn-doped compositions investigated in this study. Compositions with high Cs content exhibited lower melting points of approximately 80 °C. In addition, high Cs content materials exhibited a significant reduction in Cs release from the solid to liquid phase by leaching or aqueous corrosion as compared to low Cs content materials. These property changes would be beneficial for applications in radioactive cesium immobilization in a multi-phase ceramic by allowing for decreased processing temperatures and higher cesium weight loadings. More broadly, these results establish the link between composition, structural symmetry, and thermodynamic stability for tunnel structured ceramics with implications in the design of new energy conversion and storage materials.
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U2 - 10.1007/s10853-018-2904-1
DO - 10.1007/s10853-018-2904-1
M3 - Article
AN - SCOPUS:85053705329
SN - 0022-2461
VL - 54
SP - 1112
EP - 1125
JO - Journal of Materials Science
JF - Journal of Materials Science
IS - 2
ER -