Framework flexibility of sodium zirconium phosphate: role of disorder, and polyhedral distortions from Monte Carlo investigation

Abstract

A detailed Monte Carlo investigation of the structural changes of the framework of sodium zirconium phosphate, [Zr 2 P 3 O 12 ] -,-NASICON (acronym for NaSuperIonic CONductor)-accommodating alkali ions of varying sizes (Li ? , Na ? , K ? , Rb ? and Cs ? ) is carried out over a range of temperatures. Simulation results are critically compared with the structural models proposed earlier and available experimental results. Anisotropic changes of the rhombohedral cell parameters-a contracts while c expands with the size of the alkali ion substituted-is observed in good agreement with previous experimental results. The mechanism of anisotropic variation of lattice parameters involves dominantly, coupled rotations of the polyhedra as proposed by Alamo and co-workers. It is, however, observed that the distortions of the PO 4 tetrahedra and ZrO 6 octahedra are significant, and accounts for nearly one-third of the total change in a and c-parameters as the size of the alkali ion increases. This suggests that 'rigid' polyhedral models, permitting only angular distortions of the polyhedra, are of limited quantitative applicability in these solids. The same mechanism is found to be responsible for the low/anisotropic thermal expansion of these solids. Evidence that the polyhedral rotations are dynamic, opposed to a static-frozen-in disorder, is provided.

Role of Framework Flexibility in Ion Transport: A Molecular Dynamics Study of LiM2IV(PO4)3

“…It is interesting to note that the substitution of a larger alkali ion, A, in AZr 2 (PO 4 ) 3 , although produces an increase in the c -parameter, decreases the a -parameter in stark contrast to the present case of M IV substitution. This behavior was discussed in detail in one of the previous simulation studies …”

Sodium‐Ion Battery Electrolytes: Modeling and Simulations

“…The simulations of ceramic and glassy Na + ‐conducting materials have to a large extent followed the experimental development in the area. Focus was on β‐alumina structures in the late 1980s and 1990s, on silicate‐based glasses and Na‐Super Ionic CONductor (Nasicon) materials thereafter, while more recently there has been an increasing interest in borohydrides and phosphosulfides . Simulations targeting transport mechanisms in Na‐based SEI‐layers or mechanical properties of solid Na + ‐electrolytes have just emerged.…”

“…A decade later, Padma Kumar returned to classical MC and MD simulations of Nasicon, focusing on the structure and found an ordering of the SiO 4 and PO 4 tetrahedra ( Figure 18 ) to clearly influence the ionic conductivity. Since distinguishing between locations of P and Si is difficult using X‐ray diffraction, the simulations could aid the structural determination.…”

High temperature sodium batteries: status, challenges and future trends

“…This NASICON framework allows a wide range of chemical substitutions 65 and its exibility is responsible for its low thermal expansion, and makes it one of the most attractive families of materials for solid electrolytes. 66 Most of the studies on this family of materials have been concentrated in the composition range 1.8 < x < 2.4, presenting the highest ionic conductivity for x ¼ 2, higher than that of b-alumina which has two-dimensional mobility. In addition to its high ionic conductivity, it has claimed stability in humid air and aqueous solutions.…”