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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Na(Fe2O3)4 by Materials Project

Na(Fe2O3)4 is Spinel-like structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with six FeO4 tetrahedra and edges with six FeO6 octahedra. There are two shorter (2.21 Å) and four longer (2.25 Å) Na–O bond lengths. In the second Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with six equivalent FeO4 tetrahedra and edges with six FeO6 octahedra. There are four shorter (2.24 Å) and two longer (2.25 Å) Na–O bond lengths. There are seven inequivalent Fe+2.88+ sites. In the first Fe+2.88+ site, Fe+2.88+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one NaO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.03–2.18 Å. In the second Fe+2.88+ site, Fe+2.88+ is bonded to four O2- atoms to form FeO4 tetrahedra that share a cornercorner with one NaO6 octahedra and corners with eleven FeO6 octahedra. The corner-sharing octahedra tilt angles range from 54–60°. There is one shorter (1.88 Å) and three longer (1.98 Å) Fe–O bond length. In the third Fe+2.88+ site, Fe+2.88+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, edges with two equivalent NaO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.04–2.08 Å. In the fourth Fe+2.88+ site, Fe+2.88+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with two equivalent NaO6 octahedra and corners with ten FeO6 octahedra. The corner-sharing octahedra tilt angles range from 50–63°. There are a spread of Fe–O bond distances ranging from 1.88–2.04 Å. In the fifth Fe+2.88+ site, Fe+2.88+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three equivalent NaO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 54–61°. There is three shorter (1.91 Å) and one longer (2.03 Å) Fe–O bond length. In the sixth Fe+2.88+ site, Fe+2.88+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one NaO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.05–2.11 Å. In the seventh Fe+2.88+ site, Fe+2.88+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one NaO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.04–2.11 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Na1+ and three Fe+2.88+ atoms. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe+2.88+ atoms. In the third O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe+2.88+ atoms. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Na1+ and three Fe+2.88+ atoms. In the fifth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe+2.88+ atoms. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Fe+2.88+ atoms. In the seventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe+2.88+ atoms. In the eighth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Na1+ and three Fe+2.88+ atoms. In the ninth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Na1+ and three Fe+2.88+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(SnAs)2 by Materials Project

Na(SnAs)2 crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Na(SnAs)2 sheets oriented in the (0, 0, 1) direction. Na1+ is bonded to six equivalent As3- atoms to form edge-sharing NaAs6 octahedra. All Na–As bond lengths are 3.14 Å. Sn+2.50+ is bonded in a distorted T-shaped geometry to three equivalent As3- atoms. All Sn–As bond lengths are 2.72 Å. As3- is bonded to three equivalent Na1+ and three equivalent Sn+2.50+ atoms to form a mixture of corner and edge-sharing AsNa3Sn3 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(NbS2)2 by Materials Project

Na(NbS2)2 crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of one Na(NbS2)2 sheet oriented in the (0, 0, 1) direction. Na1+ is bonded in a 6-coordinate geometry to six S2- atoms. There are three shorter (2.82 Å) and three longer (2.83 Å) Na–S bond lengths. There are two inequivalent Nb+3.50+ sites. In the first Nb+3.50+ site, Nb+3.50+ is bonded to six S2- atoms to form distorted edge-sharing NbS6 pentagonal pyramids. There are three shorter (2.49 Å) and three longer (2.53 Å) Nb–S bond lengths. In the second Nb+3.50+ site, Nb+3.50+ is bonded to six S2- atoms to form distorted edge-sharing NbS6 pentagonal pyramids. There are three shorter (2.49 Å) and three longer (2.53 Å) Nb–S bond lengths. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Na1+ and three equivalent Nb+3.50+ atoms to form a mixture of corner, edge, and face-sharing SNa3Nb3 octahedra. In the second S2- site, S2- is bonded to three equivalent Na1+ and three equivalent Nb+3.50+ atoms to form a mixture of distorted corner, edge, and face-sharing SNa3Nb3 pentagonal pyramids. The corner-sharing octahedral tilt angles are 41°. In the third S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Nb+3.50+ atoms. In the fourth S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Nb+3.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(NbSe2)2 by Materials Project

Na(NbSe2)2 crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of one Na(NbSe2)2 sheet oriented in the (0, 0, 1) direction. Na1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are three shorter (2.96 Å) and three longer (2.97 Å) Na–Se bond lengths. There are two inequivalent Nb+3.50+ sites. In the first Nb+3.50+ site, Nb+3.50+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are three shorter (2.62 Å) and three longer (2.65 Å) Nb–Se bond lengths. In the second Nb+3.50+ site, Nb+3.50+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are three shorter (2.62 Å) and three longer (2.65 Å) Nb–Se bond lengths. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Na1+ and three equivalent Nb+3.50+ atoms to form a mixture of distorted edge, face, and corner-sharing SeNa3Nb3 octahedra. In the second Se2- site, Se2- is bonded to three equivalent Na1+ and three equivalent Nb+3.50+ atoms to form a mixture of distorted edge, face, and corner-sharing SeNa3Nb3 pentagonal pyramids. The corner-sharing octahedral tilt angles are 40°. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+3.50+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+3.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(SmS2)3 by Materials Project

SmNa(SmS2)2(S)2 crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of four hydrogen sulfide molecules; two samario molecules; and one Na(SmS2)2 sheet oriented in the (0, 0, 1) direction. In the Na(SmS2)2 sheet, Na1+ is bonded in a distorted rectangular see-saw-like geometry to four equivalent S+1.33- atoms. All Na–S bond lengths are 2.79 Å. Sm+2.33+ is bonded in a linear geometry to two equivalent S+1.33- atoms. Both Sm–S bond lengths are 2.49 Å. S+1.33- is bonded in a distorted linear geometry to one Na1+ and one Sm+2.33+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(WO3)2 by Materials Project

Na(WO3)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to twelve O2- atoms to form NaO12 cuboctahedra that share corners with four equivalent NaO12 cuboctahedra, faces with two equivalent NaO12 cuboctahedra, and faces with eight equivalent WO6 octahedra. There are eight shorter (2.64 Å) and four longer (2.94 Å) Na–O bond lengths. In the second Na1+ site, Na1+ is bonded to twelve O2- atoms to form NaO12 cuboctahedra that share corners with four equivalent NaO12 cuboctahedra, faces with two equivalent NaO12 cuboctahedra, and faces with eight equivalent WO6 octahedra. There are four shorter (2.58 Å) and eight longer (2.82 Å) Na–O bond lengths. W+5.50+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six equivalent WO6 octahedra and faces with four NaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 8–11°. All W–O bond lengths are 1.96 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Na1+ and two equivalent W+5.50+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+ and two equivalent W+5.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(VSe2)2 by Materials Project

Na(VSe2)2 is MAX Phase-like structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three Na(VSe2)2 sheets oriented in the (0, 0, 1) direction. Na1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are three shorter (2.99 Å) and three longer (3.00 Å) Na–Se bond lengths. There are two inequivalent V+3.50+ sites. In the first V+3.50+ site, V+3.50+ is bonded to six Se2- atoms to form edge-sharing VSe6 octahedra. There are three shorter (2.52 Å) and three longer (2.59 Å) V–Se bond lengths. In the second V+3.50+ site, V+3.50+ is bonded to six Se2- atoms to form edge-sharing VSe6 octahedra. There are three shorter (2.52 Å) and three longer (2.59 Å) V–Se bond lengths. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Na1+ and three equivalent V+3.50+ atoms to form a mixture of face, edge, and corner-sharing SeNa3V3 octahedra. In the second Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent V+3.50+ atoms. In the third Se2- site, Se2- is bonded to three equivalent Na1+ and three equivalent V+3.50+ atoms to form a mixture of distorted face, edge, and corner-sharing SeNa3V3 pentagonal pyramids. The corner-sharing octahedral tilt angles are 41°. In the fourth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent V+3.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

TiO x -supported Na-Mn-W oxides for the oxidative coupling of methane

Supported Na-Mn-W oxides are among the most studied catalysts for the oxidative coupling of methane (OCM) because of their superior thermal stability and relatively high C 2+ product yields. However, because of the structural complexity, the roles of each component in these catalysts have been controversial. In this work, WO x and MnO x sites were supported on titanate nanowires and employed in OCM studies. Compared to the commonly studied silica support, which is subject to severe restructuring due to the Na-induced crystallization, titanate support not only serves as a reservoir for alkali metals (e.g., Na), but also stabilizes isolated MnO x species. The catalytic performance of the titanate-based catalyst is similar to that of reference catalyst, MnO x /Na 2 WO 4 /SiO 2 , with a synergistic effect between MnO x and WO x sites. Further, advanced electron microscopy, X-ray diffraction, infrared spectroscopy, and X-ray absorption near edge structure spectroscopy suggest that the basic NaO x and MnO x species have strong interactions with the acidic WO x and TiO x species, which might contribute to the high selectivity toward C 2+ products and suppressed CO x formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

On the Electrochemical Properties of Carbon-Coated NaCrO 2 for Na-Ion Batteries

NaCrO 2 is a promising cathode for Na-ion batteries. However, further studies of the mechanisms controlling its specific capacities and cycle stability are needed for real-world applications in the future. This study reveals, for the first time, that the typical specific capacity of ~110 mAh/g reported by many researchers when the charge/discharge voltage window is set between 2.0 and 3.6 V vs. Na/Na + is actually controlled by the low electronic conductivity at the electrode/electrolyte interface. Through wet solution mixing of NaCrO 2 particles with carbon precursors, uniform carbon coating can be formed on the surface of NaCrO 2 particles, leading to unprecedented specific capacities at 140 mAh/g, which is the highest specific capacity ever reported in the literature with the lower and upper cutoff voltages at the aforementioned values. However, such carbon-coated NaCrO 2 with ultrahigh specific capacity does not improve cycle stability because with the specific capacity at 140 mAh/g the Na deintercalation during charge is more than 50% Na ions per formula unit of NaCrO 2 which leads to irreversible redox reactions. The insights from this study provide a future direction to enhance the long-term cycle stability of NaCrO 2 through integrating carbon coating and doping.

25 ENERGY STORAGE↗
DOE OSTI2021

Progress in Epitaxial Thin-Film Na 3 Bi as a Topological Electronic Material

Trisodium bismuthide (Na 3 Bi) is the first experimentally verified topological Dirac semimetal, and is a 3D analogue of graphene hosting relativistic Dirac fermions. Its unconventional momentum-energy relationship is interesting from a fundamental perspective, yielding exciting physical properties such as chiral charge carriers, the chiral anomaly, and weak anti-localization. It also shows promise for realizing topological electronic devices such as topological transistors. Herein, an overview of the substantial progress achieved in the last few years on Na 3 Bi is presented, with a focus on technologically relevant large-area thin films synthesized via molecular beam epitaxy. Key theoretical aspects underpinning the unique electronic properties of Na 3 Bi are introduced. Next, the growth process on different substrates is reviewed. Spectroscopic and microscopic features are illustrated, and an analysis of semiclassical and quantum transport phenomena in different doping regimes is provided. Furthermore, the emergent properties arising from confinement in two dimensions, including thickness-dependent and electric-field-driven topological phase transitions, are addressed, with an outlook toward current challenges and expected future progress.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Na 3 Zr 2 Si 2 PO 12 Solid Electrolyte Membrane for High‐Performance Seawater Battery

Abstract Seawater batteries (SWBs) have gained tremendous interest in the electrochemical energy storage research field because of their low cost, natural abundance, and potential use for long‐duration energy storage. Advancing a SWB to demonstration projects is plagued by the poor electrochemical performance stemming from the poor interfaces of the solid electrolyte (SE), as well as the structural and chemical instabilities and sluggish ionic transport properties. In this study, the anode compartment of a surrogate SWB is constructed with a Na | SE | hard carbon configuration, and tailored dopants are introduced into the Nasicon‐type Na 3 Zr 2 Si 2 PO 12 (NZSP) SE membrane. After doping with TiO 2 , a much more densely packed pellet with uniformly distributed porous structure is obtained. Changes in surface chemistry and local structure in the bulk are observed, which are believed to contribute to the improved ionic conductivity and higher critical current density of the TiO 2 ‐doped NZSP. Stable cycling performance with reversible capacities based on different Na storage mechanisms are also demonstrated.

25 ENERGY STORAGE↗
DOE OSTI2023

Regulating Cation Interactions for Zero–Strain and High–Voltage P2–type Na 2/3 Li 1/6 Co 1/6 Mn 2/3 O 2 Layered Oxide Cathodes of Sodium–Ion Batteries

Deep sodium extraction/insertion of sodium cathodes usually causes undesired Jahn–Teller distortion and phase transition, both of which will reduce structural stability and lead to poor long-cycle reliability. Here we report a zero-strain P2- Na 2/3 Li1/6Co 1/6 Mn 2/3 O 2 cathode, in which the lithium/cobalt substitution contributes to reinforcing the host structure by reducing the Mn 3+ /Mn 4+ redox, mitigating the Jahn–Teller distortion, and minimizing the lattice change. 94.5 % of Na + in the unit structure can be reversibly cycled with a charge cut-off voltage of 4.5 V (vs. Na + /Na). Impressively, a solid-solution reaction without phase transitions is realized upon deep sodium (de)intercalation, which poses a minimal volume deviation of 0.53 %. Finally, it attains a high discharge capacity of 178 mAh g –1 , a high energy density of 534 Wh kg –1 , and excellent capacity retention of 95.8 % at 1 C after 250 cycles.

25 ENERGY STORAGE↗
DOE OSTI2023

On the Electride Nature of Na–hP4

Early quantum mechanical models suggested that pressure drives solids towards free-electron metal behavior where the ions are locked into simple close-packed structures. The prediction and subsequent discovery of high-pressure electrides (HPEs), compounds assuming open structures where the valence electrons are localized in interstitial voids, required a paradigm shift. Our quantum chemical calculations on the iconic insulating Na-hP4 HPE show that increasing density causes a 3s→3pd electronic transition due to Pauli repulsion between the 1s2s and 3s states, and orthogonality of the 3pd states to the core. The large lobes of the resulting Na-pd hybrid orbitals point towards the center of an 11-membered penta-capped trigonal prism and overlap constructively, forming multicentered bonds, which are responsible for the emergence of the interstitial charge localization in Na-hP4. As a result, these multicentered bonds facilitate the increased density of this phase, which is key for its stabilization under pressure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Superatomic nature of metal encapsulated dodecahedrane: The case of M@ C 20 H 20 (M = Li, Na, Mg + )

The idea of designing unprecedented materials made of superatomic building blocks, motivated the present study on endohedral M@C 20 H 20 (M = Li, Na, Mg + ) species. Here, ground and excited electronic structures of M@C 20 H 20 (M = Li, Na, Mg + ) were analyzed by means of high-level quantum calculations. In their ground states, one electron occupies a defuse superatomic s-orbital that lies around the C 20 H 20 cage. These entities populate higher angular momentum p-, d-, f-, g-superatomic orbitals in their low-lying electronic states. The proposed superatomic Aufbau shell model for Li@C 20 H 20 and Na@C 20 H 20 is 1s, 1p, 1d, 2s, 1f, 2p, 2d, 1g, 2f slightly different from that of Mg@C 20 H 20 + which is 1s, 1p, 1d, 2s, 1f, 2p, 2d, 1g, 3s, 2f, 2g, 3p. These introduced superatomic orbital series resemble the Aufbau principle of solvated electron precursors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A Low-Voltage Layered Na 2 TiGeO 5 Anode for Lithium-Ion Battery

Titanium-based anode materials have achieved much progress with the wide studies in lithium-ion batteries. However, these known materials usually possess high discharge voltage platforms and limited energy densities. In this work, a titanium-based oxide of Na 2 TiGeO 5 with layered structure, two-dimensional lamellar frame and exposed highly active (001) facet, exhibiting good electrochemical performance in terms of high capacity (410 mAh g –1 with a current density of 50 mA g –1 ), excellent rate capability and cycling stability with no obvious capacity attenuation after 4000 cycles, is reported. The appropriate discharge voltage plateau at around 0.2 V endows the Na 2 TiGeO 5 anode material high security compared with graphite and high energy density compared with spinel Li 4 Ti 5 O 12 . Combining the electrochemical tests and the density functional theory calculations, the Li + storage mechanism of Na 2 TiGeO 5 is elucidated and the conversion reaction process is revealed. More importantly, this study provides a way to develop low-voltage and high-capacity titanium-based anode materials for efficient energy storage.

25 ENERGY STORAGE↗
DOE OSTI2020

Regional climate change projections from NA-CORDEX and their relation to climate sensitivity

Abstract The climate sensitivity of global climate models (GCMs) strongly influences projected climate change due to increased atmospheric carbon dioxide. Reasonably, the climate sensitivity of a GCM may be expected to affect dynamically downscaled projections. However, there has been little examination of the effect of the climate sensitivity of GCMs on regional climate model (RCM) ensembles. Therefore, we present projections of temperature and precipitation from the ensemble of projections produced as a part of the North American branch of the international Coordinated Regional Downscaling Experiment (NA-CORDEX) in the context of their relationship to the climate sensitivity of their parent GCMs. NA-CORDEX simulations were produced at 50-km and 25-km resolutions with multiple RCMs which downscaled multiple GCMs that spanned nearly the full range of climate sensitivity available in the CMIP5 archive. We show that climate sensitivity is a very important source of spread in the NA-CORDEX ensemble, particularly for temperature. Temperature projections correlate with driving GCM climate sensitivity annually and seasonally across North America not only at a continental scale but also at a local-to-regional scale. Importantly, the spread in temperature projections would be reduced if only low, mid, or high climate sensitivity simulations were considered, or if only the ensemble mean were considered. Precipitation projections correlate with climate sensitivity, but only at a continental scale during the cold season, due to the increasing influence of other processes at finer scales. Additionally, it is shown that the RCMs do alter the projection space sampled by their driving GCMs.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

In situ probing the origin of interfacial instability of Na metal anode

The unstable and fragile solid electrolyte interphase (SEI) has restricted the application of Na metal anodes. Despite numerous research efforts being put into understanding its chemical composition and physical properties, direct observation of its formation remains a challenge due to the lack of temporal and spatial resolution. Here, through combined in situ probing techniques, we exhibit two pivotal stages associated with SEI instability during the often -neglected formation process. It is revealed that Na metal that is not uniformly passivated at the initial (passivating) stage will trigger unrestricted electrolyte decomposition and homogeneous components distribution during the subsequent (growing) stage. SEI with homogenously distributed components is found to have higher solubility than that with a layered structure evolved from a compact passivation layer. Furthermore, through demonstrating an SEI dissolution model that is closely related to its formation process and compositional distribution, this work sheds light on an uncharted territory of Na metal batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Heat capacity and thermodynamic functions of partially dehydrated cation-exchanged (Na + , Cs + , Cd 2+ , Li + , and NH 4 + ) $\mathrm{RHO}$ zeolites

Synthetic zeolites have a myriad of applications in industry due to their porous frameworks, potential to exhibit flexibility, and specific interactions with guest molecules. One topology of zeolites, RHO, is known to be flexible and have strong interactions with both H 2 O and CO 2 . Here we have performed heat capacity measurements on three partially dehydrated zeolite RHO samples containing extra-framework cations Na + and Cs + , Cd 2+ and Cs + , and Li + and NH 4 + to understand the energetics of these materials. Based on fits of the heat capacity data, we report smooth thermodynamic functions of C p,m , Δ T 0 S m °, Δ T 0 H m °, and Φ m ° for these samples. The standard S m ° at 298.15 K are 76.3 ± 0.8, 72.1 ± 0.8, and 68.8 ± 0.7 J∙K -1 ∙mol -1 for the Na,Cs RHO, Cd,Cs RHO, and Li,NH 4 RHO samples, respectively, and the standard H m ° at 298.15 K are 12.1 ± 0.1, 11.4 ± 0.1, and 11.4 ± 0.1 kJ∙mol -1 . Our measurements also show a transition in the heat capacity of Na,Cs RHO, the sample with the highest water content, between 180 and 300 K that is not clearly observed in the other two samples. We attribute this transition to labile water and cations in the framework. This movement could also be coupled with a temperature-induced lattice expansion. Future work will include heat capacity measurements on fully dehydrated and fully hydrated zeolite RHO in order to separate these two possible phenomena.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗