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Kyle S. Brinkman - One of the best experts on this subject based on the ideXlab platform.
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radiation damage and thermal annealing in tunnel structured Hollandite materials
Acta Materialia, 2021Co-Authors: Mingyang Zhao, Eric C Oquinn, Nancy Birkner, Maik Lang, Kyle S. BrinkmanAbstract:Abstract Three tunnel structured Hollandite samples (Cs1.33Ga1.33Ti6.67O16, Cs1.33Fe1.33Ti6.67O16, and Cs1.33Zn0.67Ti7.33O16) with demonstrated thermodynamic stability and chemical durability were synthesized and irradiated by a 1.1 GeV Au ion beam in order to study effects of B-site dopants on radiation stability. A crystalline-to-amorphous transformation induced by the high-energy ion irradiation was confirmed by complementary characterization techniques sensitive to different length-scales, such as powder X-ray diffraction, Raman spectroscopy and neutron total scattering. High-temperature oxide melt solution calorimetry was performed to determine the energy landscape before and after ion irradiation. Together, structural and thermodynamic analyses demonstrated distinctly different radiation responses of the Hollandite with different B-site dopants; the Ga-substituted Hollandite exhibited the smallest enthalpy of damage indicating the best radiation stability among the three samples. The hypothesized origin of the different radiation responses is the structural feature in the binary oxide form of the respective B-site dopants (e.g., Ga2O3 versus Fe2O3/ZnO for Ga and Fe/Zn dopants, respectively). Moreover, thermal analysis (i.e., differential scanning calorimetry) was conducted to investigate structural changes from the irradiation induced damaged states after thermal annealing. Results of thermal analysis revealed that the annealing-induced structural evolution of the radiation damaged Hollandite structure is complex and decoupled at different length-scales. The long-range periodic structure (nanometers) was not recovered after thermal annealing and structural changes over a shorter range (≤ ∼3 A) occurred in multiple steps during the annealing process.
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radiation damage and thermal annealing in tunnel structured Hollandite materials
Social Science Research Network, 2020Co-Authors: Mingyang Zhao, Eric C Oquinn, Nancy Birkner, Maik Lang, Kyle S. BrinkmanAbstract:Three tunnel structured Hollandite samples (Cs 1.33 Ga 1.33 Ti 6.67 O 16 , Cs 1.33 Fe 1.33 Ti 6.67 O 16 , and Cs 1.33 Zn 0.67 Ti 7.33 O 16 ) with demonstrated thermodynamic stability and chemical durability were synthesized and irradiated by a 1 GeV Au ion beam in order to study effects of B-site dopants on radiation stability. The structural changes induced by radiation were analyzed by complementary characterization techniques at different length-scales, such as powder X-ray diffraction, Raman spectroscopy and neutron total scattering. High-temperature oxide melt solution calorimetry was performed to determine the energy landscape before and after radiation. Together, structural and thermodynamic analyses demonstrated distinctly different radiation responses of the Hollandite with different B-site dopants. The hypothesized origin of these differences is the structural feature in the binary oxide form of the respective B-site dopants (e.g., Ga 2 O 3 versus ZnO for Ga and Zn dopants, respectively). Moreover, thermal analysis (i.e., differential scanning calorimetry) was conducted to investigate structural changes from the radiation induced damaged states after thermal annealing. Results of thermal analysis revealed that the annealing-induced structural evolution of the radiation damaged Hollandite structure is complex and decoupled at different length-scales. The long-range periodic structure (nanometers) was not recovered after thermal annealing and structural changes over a shorter range (≤ ~3 A) occurred in multiple steps during the annealing process.
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Exploring the links between crystal chemistry, cesium retention, thermochemistry and chemical durability in single-phase (Ba,Cs)_1.33(Fe,Ti)_8O_16 Hollandite
Journal of Materials Science, 2020Co-Authors: Mingyang Zhao, Lindsay Shuller-nickles, Patrick Russell, Jake Amoroso, Scott Misture, Stephen Utlak, Theodore Besmann, Kyle S. BrinkmanAbstract:A series of single-phase Fe-substituted Hollandite (Ba,Cs)_1.33(Fe,Ti)_8O_16 compositions with the chemical formula Ba_1.33− x Cs_ x Fe_2.66− x Ti_5.34+ x O_16 ( x = 0, 0.1, 0.2, 0.667, and 1.33) were systematically investigated using both experimental and computational methods to establish possible links between crystal chemistry, Cs retention, thermochemistry and chemical durability. A phase transition from monoclinic to tetragonal was observed as a function of both Cs content and temperature. Elemental analysis revealed that Cs retention was significantly improved for the Hollandite with higher Cs content. High-temperature melt solution calorimetry and sublattice-based thermodynamic simulations confirmed a high degree of thermodynamic stability in the Fe-substituted compounds which was enhanced in compositions with higher Cs content. This trend can be primarily attributed to two factors: (1) a decreasing ratio of the average ionic radii of B-site cations to that of A-site cations and (2) an increasing tolerance factor. Based on a reoptimized sublattice model, a pseudo-ternary phase diagram was generated to predict the optimal composition possessing the highest Cs content and A-site occupancy, which had not been experimentally explored. Leaching tests further verified that high Cs-containing compositions have significant chemical durability.
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Radiation tolerant ceramics for nuclear waste immobilization: Structure and stability of cesium containing Hollandite of the form (Ba,Cs)1.33(Zn,Ti)8O16 and (Ba,Cs)1.33(Ga,Ti)8O16
Journal of Nuclear Materials, 2019Co-Authors: Rob Grote, Ming Tang, Jake W Amoroso, Tao Hong, Lindsay Shuller-nickles, Kyle S. BrinkmanAbstract:Abstract The radiation damage tolerance of nuclear waste forms is dependent on the material's resistance to defect formation and its ability to accommodate structural distortions that arise from defect creation. This study illustrates how the radiation tolerance of Hollandite can be improved thorough compositional control of cesium stoichiometry. A Hollandite series with the general form BaxCsyZnx+y/2Ti8-x-y/2O16 (0
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compositional control of tunnel features in Hollandite based ceramics structure and stability of ba cs 1 33 zn ti 8o16
Journal of Materials Science, 2019Co-Authors: Rob Grote, Ming Tang, Jake W Amoroso, Alexandra Navrotsky, Lindsay Shullernickles, Mingyang Zhao, Weiping Gong, Kristina Lilova, Kyle S. BrinkmanAbstract: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.
Jake W Amoroso - One of the best experts on this subject based on the ideXlab platform.
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compositional control of tunnel features in Hollandite based ceramics structure and stability of ba cs 1 33 zn ti 8o16
Journal of Materials Science, 2019Co-Authors: Rob Grote, Ming Tang, Jake W Amoroso, Alexandra Navrotsky, Lindsay Shullernickles, Mingyang Zhao, Weiping Gong, Kristina Lilova, Kyle S. BrinkmanAbstract: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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Radiation tolerant ceramics for nuclear waste immobilization: Structure and stability of cesium containing Hollandite of the form (Ba,Cs)1.33(Zn,Ti)8O16 and (Ba,Cs)1.33(Ga,Ti)8O16
Journal of Nuclear Materials, 2019Co-Authors: Rob Grote, Ming Tang, Jake W Amoroso, Tao Hong, Lindsay Shuller-nickles, Kyle S. BrinkmanAbstract:Abstract The radiation damage tolerance of nuclear waste forms is dependent on the material's resistance to defect formation and its ability to accommodate structural distortions that arise from defect creation. This study illustrates how the radiation tolerance of Hollandite can be improved thorough compositional control of cesium stoichiometry. A Hollandite series with the general form BaxCsyZnx+y/2Ti8-x-y/2O16 (0
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radiation damage of Hollandite in multiphase ceramic waste forms
Journal of Nuclear Materials, 2017Co-Authors: Braeden M Clark, S K Sundaram, Jake W Amoroso, James C Marra, Priyatham Tumurgoti, V Shutthanandan, Ming TangAbstract:Abstract Radiation damage was simulated in multiphase titanate-based ceramic waste forms using an ion accelerator to generate high energy alpha particles (He + ) and an ion implanter to generate 7 MeV gold (Au 3+ ) particles. X-ray diffraction and transmission electron microscopy were used to characterize the damaged surfaces and nearby regions. Simulated multiphase ceramic waste forms were prepared using two processing methods: spark plasma sintering and melt-processing. Both processing methods produced ceramics with similar phase assemblages consisting of Hollandite-, zirconolite/pyrochlore-, and perovskite-type phases. The measured heavy ion (Au 3+ ) penetration depth was less in spark plasma sintered samples than in melt-processed samples. Structural breakdown of the Hollandite phase occurred under He + irradiation indicated by the presence of x-ray diffraction peaks belonging to TiO 2 , BaTiO 5 , and other Hollandite related phases (Ba 2 Ti 9 O 20 ). The composition of the constituent Hollandite phase affected the extent of damage induced by Au 3+ ions.
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cesium incorporation in Hollandite rich multiphasic ceramic waste forms
Journal of Solid State Chemistry, 2017Co-Authors: Priyatham Tumurugoti, Braeden M Clark, Jake W Amoroso, D J Edwards, S K SundaramAbstract:Abstract Hollandite-rich multiphase waste form compositions processed by melt-solidification and spark plasma sintering (SPS) were characterized, compared, and validated for nuclear waste incorporation. Phase identification by x-ray diffraction (XRD) and electron back-scattered diffraction (EBSD) confirmed Hollandite as the major phase present in these samples along with perovskite, pyrochlore and zirconolite. Distribution of selected elements observed by wavelength dispersive spectroscopy (WDS) maps indicated that Cs formed a secondary phase during SPS processing, which was considered undesirable. On the other hand, Cs partitioned into the Hollandite phase in melt-processed samples. Further analysis of Hollandite structure in melt-processed composition by selected area electron diffraction (SAED) revealed ordered arrangement of tunnel ions (Ba/Cs) and vacancies, suggesting efficient Cs incorporation into the lattice.
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heavy ion irradiations on synthetic Hollandite type materials ba1 0cs0 3a2 3ti5 7o16 a cr fe al
Journal of Solid State Chemistry, 2016Co-Authors: Ming Tang, Priyatham Tumurugoti, Braeden M Clark, S K Sundaram, Jake W Amoroso, James C Marra, Cheng Sun, Yongqiang Wang, Ying Bing JiangAbstract:Abstract The Hollandite supergroup of minerals has received considerable attention as a nuclear waste form for immobilization of Cs. The radiation stability of synthetic Hollandite-type compounds described generally as Ba1.0Cs0.3A2.3Ti5.7O16 (A=Cr, Fe, Al) were evaluated by heavy ion (Kr) irradiations on polycrystalline single phase materials and multiphase materials incorporating the Hollandite phases. Ion irradiation damage effects on these samples were examined using grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). Single phase compounds possess tetragonal structure with space group I4/m. GIXRD and TEM observations revealed that 600 keV Kr irradiation-induced amorphization on single phase Hollandites compounds occurred at a fluence between 2.5×1014 Kr/cm2 and 5×1014 Kr/cm2. The critical amorphization fluence of single phase Hollandite compounds obtained by in situ 1 MeV Kr ion irradiation was around 3.25×1014 Kr/cm2. The Hollandite phase exhibited similar amorphization susceptibility under Kr ion irradiation when incorporated into a multiphase system.
Ming Tang - One of the best experts on this subject based on the ideXlab platform.
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Radiation tolerant ceramics for nuclear waste immobilization: Structure and stability of cesium containing Hollandite of the form (Ba,Cs)1.33(Zn,Ti)8O16 and (Ba,Cs)1.33(Ga,Ti)8O16
Journal of Nuclear Materials, 2019Co-Authors: Rob Grote, Ming Tang, Jake W Amoroso, Tao Hong, Lindsay Shuller-nickles, Kyle S. BrinkmanAbstract:Abstract The radiation damage tolerance of nuclear waste forms is dependent on the material's resistance to defect formation and its ability to accommodate structural distortions that arise from defect creation. This study illustrates how the radiation tolerance of Hollandite can be improved thorough compositional control of cesium stoichiometry. A Hollandite series with the general form BaxCsyZnx+y/2Ti8-x-y/2O16 (0
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compositional control of tunnel features in Hollandite based ceramics structure and stability of ba cs 1 33 zn ti 8o16
Journal of Materials Science, 2019Co-Authors: Rob Grote, Ming Tang, Jake W Amoroso, Alexandra Navrotsky, Lindsay Shullernickles, Mingyang Zhao, Weiping Gong, Kristina Lilova, Kyle S. BrinkmanAbstract: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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radiation damage of Hollandite in multiphase ceramic waste forms
Journal of Nuclear Materials, 2017Co-Authors: Braeden M Clark, S K Sundaram, Jake W Amoroso, James C Marra, Priyatham Tumurgoti, V Shutthanandan, Ming TangAbstract:Abstract Radiation damage was simulated in multiphase titanate-based ceramic waste forms using an ion accelerator to generate high energy alpha particles (He + ) and an ion implanter to generate 7 MeV gold (Au 3+ ) particles. X-ray diffraction and transmission electron microscopy were used to characterize the damaged surfaces and nearby regions. Simulated multiphase ceramic waste forms were prepared using two processing methods: spark plasma sintering and melt-processing. Both processing methods produced ceramics with similar phase assemblages consisting of Hollandite-, zirconolite/pyrochlore-, and perovskite-type phases. The measured heavy ion (Au 3+ ) penetration depth was less in spark plasma sintered samples than in melt-processed samples. Structural breakdown of the Hollandite phase occurred under He + irradiation indicated by the presence of x-ray diffraction peaks belonging to TiO 2 , BaTiO 5 , and other Hollandite related phases (Ba 2 Ti 9 O 20 ). The composition of the constituent Hollandite phase affected the extent of damage induced by Au 3+ ions.
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heavy ion irradiations on synthetic Hollandite type materials ba1 0cs0 3a2 3ti5 7o16 a cr fe al
Journal of Solid State Chemistry, 2016Co-Authors: Ming Tang, Priyatham Tumurugoti, Braeden M Clark, S K Sundaram, Jake W Amoroso, James C Marra, Cheng Sun, Yongqiang Wang, Ying Bing JiangAbstract:Abstract The Hollandite supergroup of minerals has received considerable attention as a nuclear waste form for immobilization of Cs. The radiation stability of synthetic Hollandite-type compounds described generally as Ba1.0Cs0.3A2.3Ti5.7O16 (A=Cr, Fe, Al) were evaluated by heavy ion (Kr) irradiations on polycrystalline single phase materials and multiphase materials incorporating the Hollandite phases. Ion irradiation damage effects on these samples were examined using grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). Single phase compounds possess tetragonal structure with space group I4/m. GIXRD and TEM observations revealed that 600 keV Kr irradiation-induced amorphization on single phase Hollandites compounds occurred at a fluence between 2.5×1014 Kr/cm2 and 5×1014 Kr/cm2. The critical amorphization fluence of single phase Hollandite compounds obtained by in situ 1 MeV Kr ion irradiation was around 3.25×1014 Kr/cm2. The Hollandite phase exhibited similar amorphization susceptibility under Kr ion irradiation when incorporated into a multiphase system.
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melt processed single phase Hollandite waste forms for nuclear waste immobilization ba1 0cs0 3a2 3ti5 7o16 a cr fe al
Journal of Alloys and Compounds, 2014Co-Authors: Jake W Amoroso, Ming Tang, James C Marra, S D Conradson, Kyle S. BrinkmanAbstract:Abstract Cs is one of the more problematic fission product radionuclides to immobilize due to its high volatility at elevated temperatures, ability to form water soluble compounds, and its mobility in many host materials. The Hollandite structure is a promising crystalline host for Cs immobilization and has been traditionally fabricated by solid state sintering methods. This study presents the structure and performance of Ba1.0Cs0.3A2.3Ti5.7O16; A = Cr, Fe, Al Hollandite fabricated by melt processing. Melt processing is considered advantageous given that melters are currently in use for High Level Waste (HLW) vitrification in several countries. This work details the impact of Cr additions that were demonstrated to (i) promote the formation of a Cs containing Hollandite phase and (ii) maintain the stability of the Hollandite phase in reducing conditions anticipated for multiphase waste form processing.
Takumi Kikegawa - One of the best experts on this subject based on the ideXlab platform.
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Formation of a metastable Hollandite phase from amorphous plagioclase: A possible origin of lingunite in shocked chondritic meteorites
Physics of the Earth and Planetary Interiors, 2017Co-Authors: Tomoaki Kubo, Seiichiro Uehara, Yuji Higo, Yoshinori Tange, Mari Kono, Takumi Kato, Masahiro Imamura, Tadashi Kondo, Takumi KikegawaAbstract:Abstract We conducted high-pressure experiments in plagioclase with different anorthite contents at 18–27 GPa and 25–1750 °C using both a laser-heated diamond anvil cell and a Kawai-type multi-anvil apparatus to clarify the formation conditions of the Hollandite phase in shocked chondritic and Martian meteorites. Lingunite (NaAlSi 3 O 8 -rich Hollandite) was found first to crystallize from amorphous oligoclase as a metastable phase before decomposing into the final stable state. This process might account for the origin of lingunite found along with maskelynite in shocked chondritic meteorites. Metastable lingunite appeared at ∼20–24 GPa and ∼1100–1300 °C in laboratory tests lasting tens of minutes; however, it might also form at the higher temperatures and shorter time periods of shock events. In contrast, the Hollandite phase was not observed during any stage of crystallization when using albite or labradorite as starting materials. The formation process of (Ca,Na)-Hollandite in the labradorite composition found in Martian shergottites remains unresolved. The orthoclase contents of the Hollandite phase both in shocked meteorites (2.4–8.2 mol%) and our oligoclase sample (3.9 mol%) are relatively high compared to the albite and labradorite samples (0.6 and 1.9 mol%, respectively). This might critically affect the crystallization kinetics of Hollandite phase.
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Hollandite ii phase in kalsi3o8 as a potential host mineral of potassium in the earth s lower mantle
Physics of the Earth and Planetary Interiors, 2008Co-Authors: Naohisa Hirao, Tadashi Kondo, Eiji Ohtani, Takeshi Sakai, Takumi KikegawaAbstract:Abstract High-pressure and high-temperature experiments on the KAlSi3O8 composition were conducted in a laser-heated diamond-anvil cell at pressures up to 128 GPa, which correspond to the lowermost mantle conditions. In situ synchrotron X-ray diffraction measurements revealed that the Hollandite II phase in KAlSi3O8 with a monoclinic symmetry of I2/m was stable over the entire range of mantle conditions, and the tunnel structure formed by the double chains of edge-sharing (Si,Al)O6 octahedra, which could accommodate a larger cation such as potassium, was sustained. The (Si,Al)O6 octahedra in the KAlSi3O8 Hollandite II phase showed a similar compression behavior to those in high-pressure silicate structures, such as rutile-type and perovskite-type phases, and were found to be less compressible than the KO8 polyhedra. The KAlSi3O8 Hollandite II phase is a potential host mineral for potassium under lower mantle conditions and, therefore, may have a significant influence on geochemistry if potassium feldspar KAlSi3O8 in the Earth's crust is transported into the Earth's mantle through subduction.
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equation of state and phase transition in kalsi3o8 Hollandite at high pressure
American Mineralogist, 2006Co-Authors: T Ferroir, Tetsuo Irifune, Norimasa Nishiyama, Tsuyoshi Onozawa, Takehiko Yagi, Sebastien Merkel, Nobuyoshi Miyajima, Takumi KikegawaAbstract:The tetragonal Hollandite structure (KAlSi3O8 Hollandite) has been studied up to 32 GPa at room temperature using high-pressure in-situ X-ray diffraction techniques. A phase transformation from tetragonal I4/m phase to a new phase was found to occur at about 20 GPa. This transition is reversible on release of pressure without noticeable hysteresis and hence this new high-pressure phase is unquenchable to ambient conditions. The volume change associated with the transition is found to be small (not measurable), suggesting a second order transition. The diffraction pattern of the high-pressure phase can be indexed in a monoclinic unit cell (space group I2/m), which is isostructual with BaMn8O16 Hollandite. The {gamma} angle of the monoclinic unit cell increases continuously above the transition. A Birch-Murnaghan equation of state fit to pressure-volume data obtained for KAlSi3O8 Hollandite yields a bulk modulus K0 = 201.4 (7) GPa with K'0 = 4.0.
Lindsay Shullernickles - One of the best experts on this subject based on the ideXlab platform.
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compositional control of tunnel features in Hollandite based ceramics structure and stability of ba cs 1 33 zn ti 8o16
Journal of Materials Science, 2019Co-Authors: Rob Grote, Ming Tang, Jake W Amoroso, Alexandra Navrotsky, Lindsay Shullernickles, Mingyang Zhao, Weiping Gong, Kristina Lilova, Kyle S. BrinkmanAbstract: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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atomistic scale investigation of cation ordering and phase stability in cs substituted ba 1 33 zn 1 33 ti 6 67 o 16 ba 1 33 ga 2 66 ti 5 67 o 16 and ba 1 33 al 2 66 ti 5 33 o 16 Hollandite
Scientific Reports, 2018Co-Authors: Yi Wen, Kyle S. Brinkman, Lindsay ShullernicklesAbstract:The titanate-based Hollandite structure is proposed as an effective ceramic waste form for Cs-immobilization. In this study, quantum-mechanical calculations were used to quantify the impact of A-site and B-site ordering on the structural stability of Hollandite with compositions BaxCsy(MzTi8-z)O16, where M = Zn2+, Ga3+, and Al3+. The calculated enthalpy of formation agrees with experimental measurements of related Hollandite phases from melt solution calorimetry. Ground state geometry optimizations show that, for intermediate compositions (e.g., CsBaGa6Ti18O48), the presence of both Cs and Ba in the A-site tunnels is not energetically favored. However, the decay heat generated during storage of the Cs-containing waste form may overcome the energetics of Ba and Cs mixing in the tunnel structure of Hollandite. The ability of the Hollandite structure to accommodate the radioparagenesis of Cs to Ba is critical for long term performance of the waste. For the first time, B-site ordering was observed along the tunnel direction ([001] zone axis) for the Ga-Hollandite compositions, as well as the intermediate Al-Hollandite composition. These compositionally dependent structural features, and associated formation enthalpies, are of importance to the stability and radiation damage tolerance of ceramic waste forms.