Local structure of glassy lithium phosphorus oxynitride thin films: a combined experimental and ab initio approach

Lithium phosphorus oxynitride (LiPON) is an amorphous solid-state lithium ion conductor displaying exemplary cyclability against lithium metal anodes. There is no definitive explanation for this stability due to the limited understanding of the structure of LiPON. We provide a structural model of RF-sputtered LiPON via experimental and computational spectroscopic methods. Information about the short-range structure results from 1D and 2D solid-state nuclear magnetic resonance experiments investigating chemical shift anisotropy and dipolar interactions. These results are compared with first principles chemical shielding calculations of Li-P-O/N crystals and ab initio molecular dynamics-generated amorphous LiPON models to unequivocally identify the glassy structure as primarily isolated phosphate monomers with N incorporated in both apical and as bridging sites in phosphate dimers. Structural results suggest LiPON's stability is a result of its glassy character. Free-standing LiPON films are produced that exhibit a high degree of flexibility highlighting the unique mechanical properties of glassy materials

LiSi3As6 and Li2SiAs2 with flexible SiAs2 polyanions: synthesis, structure, bonding, and ionic conductivity

Two novel ternary phases, LiSi3As6 and Li2SiAs2, have been synthesized and characterized. Both phases have an identical Si : As ratio of 1 : 2 providing insight on how layers of the parent phase SiAs2 accommodate excess electrons from Li cations to form Si–As anionic frameworks. LiSi3As6 exhibits a variety of bonding schemes involving Si–Si and As–As bonds, as well as corner-sharing SiAs4 tetrahedra, while Li2SiAs2 is isostructural to the previously reported Li2SiP2, with adamantane-like Si4As10 units connected into 3D framework. LiSi3As6 and Li2SiAs2 are predicted to be indirect semiconductors which was experimentally confirmed by optical properties characterization. Li2SiAs2 exhibits low thermal conductivity of 1.20 W m−1 K−1 at 300 K in combination with a room temperature ionic conductivity of 7 × 10−6 S cm−1, an order of magnitude greater than that of the phosphide and nitride analogues, indicating its potential as a solid-state Li-ion conductor

Proton NMR Relaxometry as a Rapid and Non-Destructive Technique for Probing Degradation of Supported Poly(ethylenimine) for CO2 Direct Air Capture

Aminopolymer-based adsorbents are commonly investigated for CO2 direct air capture (DAC). In the presence of high temperature and O2, which could happen during process upset, oxidative degradation can significantly contribute to limiting the adsorbent lifetime. Here, we demonstrate the use of a portable, benchtop NMR sensor to collect proton relaxometry profiles to track the degradation of a PEI/Al2O3 sample exposed to controlled accelerated oxidation conditions and correlate the extent of oxidation as measured by loss in amine efficiency with T2 (spin-spin) relaxation times. We hypothesize that T2 relaxation accurately tracks oxidative degradation in aminopolymers because of reduced polymer mobility resulting from radical-induced crosslinking that can occur during the oxidation process. The advantage of using NMR relaxometry as a non-destructive technique to probe degradation is demonstrated on a 1-inch square-channel monolith adsorbent exposed to actual DAC service conditions, highlighting the potential for using this technique as a rapid and non-destructive method of probing adsorbent health

Enhanced Hydrogen Bonding via Epoxide-functionalization Restricts Mobility in Poly(ethylenimine) for CO2 Capture

Epoxide-functionalization has emerged as an effective strategy for enhancing the oxidative stability of poly(ethylenimine)-based CO2 capture sorbents. However, the underlying mechanism remains largely unexplored. Here we combine first-principles modeling, material synthesis, and characterizations to investigate the impact of epoxide-functionalization on hydrogen bonding and mobility in poly(ethylenimine) (PEI). Blue-moon ensemble and deep potential molecular dynamics simulations reveal that epoxide-functionalization leads to stronger hydrogen bonding involving hydroxyl groups. Synthesized branched PEI samples with and without propylene-oxide (PO) functionalization are characterized using DSC, NMR relaxometry, and fluorescent probes, demonstrating that PO-functionalization significantly reduces BPEI mobility. These findings suggest that the enhanced oxidative stability of epoxide-functionalized PEI can be attributed to the formation of strong hydrogen bonds with hydroxyl groups, which restrict the mobility of PEI and decelerate mobility-dependent radical propagation reactions responsible for polymer degradation. Strategies for further tuning hydrogen bond environment are proposed based on these findings

Chemical Bonding and Transport Properties in Clathrates‑I with Cu–Zn–P Frameworks

Quaternary clathrate-I phases with an overall composition of Ba₈<i>M</i>_16+yP_30‑y (M = Cu,Zn) exhibit complex structural chemistry. Characterization of the electronic structures and chemical bonding using quantum-chemical calculations and ³¹P solid state NMR spectroscopy demonstrated that the Cu–Zn–P framework is flexible and able to accommodate up to six Zn atoms per formula unit via bonding rearrangements, such as partial Zn/P substitution and the formation of Cu–Zn bonds. Such perturbations of the framework’s bonding affect the thermal and charge transport properties. The overall thermoelectric figure-of-merit, <i>ZT</i>, of Ba₈Cu₁₄Zn₂P₃₀ is 0.62 at 800 K, which is 9 times higher than the thermoelectric performance of the ternary parent phase Ba₈Cu₁₆P₃₀. Through a combination of inelastic neutron scattering and single crystal X-ray diffraction experiments at 10 K, low-energy rattling of the Ba guest atoms inside the large tetrakaidecahedral cages are shown to be the reason for the low thermal conductivities observed for the studied clathrates

Chemical Bonding and Transport Properties in Clathrates‑I with Cu–Zn–P Frameworks

Quaternary clathrate-I phases with an overall composition of Ba₈<i>M</i>_16+yP_30‑y (M = Cu,Zn) exhibit complex structural chemistry. Characterization of the electronic structures and chemical bonding using quantum-chemical calculations and ³¹P solid state NMR spectroscopy demonstrated that the Cu–Zn–P framework is flexible and able to accommodate up to six Zn atoms per formula unit via bonding rearrangements, such as partial Zn/P substitution and the formation of Cu–Zn bonds. Such perturbations of the framework’s bonding affect the thermal and charge transport properties. The overall thermoelectric figure-of-merit, <i>ZT</i>, of Ba₈Cu₁₄Zn₂P₃₀ is 0.62 at 800 K, which is 9 times higher than the thermoelectric performance of the ternary parent phase Ba₈Cu₁₆P₃₀. Through a combination of inelastic neutron scattering and single crystal X-ray diffraction experiments at 10 K, low-energy rattling of the Ba guest atoms inside the large tetrakaidecahedral cages are shown to be the reason for the low thermal conductivities observed for the studied clathrates