Lattice Dynamics in the NASICON NaZr2(PO4)3 Solid Electrolyte from Temperature-Dependent Neutron Diffraction, NMR, and Ab Initio Computational Studies

Crystal structure solution and high-temperature thermal expansion in NaZr2(PO4)3-type materials

The NaZr2P3O12 family of materials have shown low and tailorable thermal expansion properties. In this study, SrZr4P6O24 (SrO·4ZrO2·3P2O5), CaZr4P6O24 (CaO·4ZrO2·3P2O5), MgZr4P6O24 (MgO·4ZrO2·3P2O5), NaTi2P3O12 [½(Na2O·4TiO2·3P2O5)], NaZr2P3O12 [½(Na2O·4ZrO2·3P2O5)], and related solid solutions were synthesized using the organic-inorganic steric entrapment method. The samples were characterized by in-situ high-temperature X-ray diffraction from 25 to 1500°C at the Advanced Photon Source and National Synchrotron Light Source II. The average linear thermal expansion of SrZr4P6O24 and CaZr4P6O24 was between -1 × 10-6 per °C and 6 × 10-6 per °C from 25 to 1500°C. The crystal structures of the high-temperature polymorphs of CaZr4P6O24 and SrZr4P6O24 with R3c symmetry were solved by Fourier difference mapping and Rietveld refinement. This polymorph is present above ∼1250°C. This work measured thermal expansion coefficients to 1500°C for all samples and investigated the differences in thermal expansion mechanisms between polymorphs and between compositions.

The applications of solid-state NMR and MRI techniques in the study of rechargeable sodium-ion batteries

In order to develop new electrode and electrolyte materials for advanced sodium-ion batteries (SIBs), it is crucial to understand a number of fundamental issues. These include the compositions of the bulk and interface, the structures of the materials used, and the electrochemical reactions in the batteries. Solid-state NMR (SS-NMR) has unique advantages in characterizing the local or microstructure of solid electrode/electrolyte materials and their interfaces-one such advantage is that these are determined in a noninvasive and nondestructive manner at the atomic level. In this review, we provide a survey of the recent advances in the understanding of the fundamental issues of SIBs using advanced NMR techniques. First, we summarize the applications of SS-NMR in characterizing electrode material structures and solid electrolyte interfaces (SEI). In particular, we elucidate the key role of in-situ NMR/MRI in revealing the complex reactions and degradation mechanisms of SIBs. Next, the characteristics and shortcomings of SS-NMR and MRI techniques in SIBs are also discussed in comparison to similar Li-ion batteries. Finally, an overview of SS-NMR and MRI techniques for sodium batteries are briefly discussed and presented.

Theoretical simulation study on crystal property and hygroscopicity of ADN doping with nitramine explosives (RDX, HMX, and CL-20)

To effectively modify the strong hygroscopicity of ammonium dinitramide (ADN) crystal, the modification of ADN crystal in the 298 K under vacuum environment was studied through theoretical calculation. Three kinds of energetic nitramine molecules (X = RDX, HMX, and CL-20) were inserted into ADN crystal in different proportions (the molecular ratios of ADN to X are 6/1, 12/1, 18/1, and 24/1), to form a total of 12 kinds of designed ADN crystals. The results show that with the modification of ADN crystal with RDX, HMX, and CL-20, the crystal space group, cell parameters, crystal density, and growth morphology will be changed under vacuum conditions. According to the analyses of adsorption heat data, four proportional modification systems all reduced the hygroscopicity of ADN crystal to varying degrees. It is worth noting that the hygroscopicity of modified ADN crystal tends to decrease with the increase of the proportion of doping molecules, but the stability gradually deteriorates, especially 18ADN/1CL-20 and 24ADN/1CL-20. Although they have an excellent anti-moisture effect, from the perspective of crystal energy stability, the actual syntheses of these two kinds of crystal cells are the most difficult. Combined with the energy stability and hygroscopicity analysis, 1HMX/24ADN crystal is a more suitable anti-hygroscopicity modification scheme among the doped ADN crystals. In this case, the isothermal adsorption heat of ADN crystal decreases from 0.692 kcal/mol to 0.573 kcal/mol. The theoretical simulation study of ADN doping modification in a vacuum will provide significant references for ADN modification in the actual situation.