P2 Type Layered Solid-State Electrolyte Na₂Zn₂TeO₆: Crystal Structure and Stacking Faults

Abstract

The layered super-ionic conductor Na2Zn2TeO6 is a promising material for applications as electrolyte in solid-state batteries. Independent of synthesis route and conditions, a significant peak broadening of (1 0 1) is evident in collected X-ray diffraction data, which is not compatible with the standard structure model (space group P6322). In this work, we describe sodium disorder and stacking faults in Na2Zn2TeO6 and identify the nature of the faults that are manifested by this peak broadening. First principle modeling was applied to describe the Na-distribution and support models on stacking faults. We describe the dominant fault as an in-plane shift causing local alignment of Te atoms along the layer stacking direction. This was experimentally verified by first constructing a supercell model of Na2Zn2TeO6 and simulating X-ray diffraction patterns for different densities of stacking faults, to help identifying a structural model that best matches experimental data. The Rietveld and in particular the stacking fault refinements, were found to perfectly describe the crystal structure and also the peak-broadening features. The stacking fault density in Na2Zn2TeO6 is ∼3%. This value appeared not to be susceptible to differences in synthesis conditions, including quenching and long-term annealing, as furthermore confirmed by in-situ X-ray diffraction data at temperatures between 25–600°C.

Insights into Crystal Structure and Diffusion of Biphasic Na2Zn2TeO6

“…Crystallographic information for the involved P2 and O′3-type phases is summarized in Tables S4 and S5. Note that the still imperfect fit of the diffraction peaks in the 2θ-range 3.5–5.0° is due to the presence of stacking faults in the P2-type phase, or possibly a P2/O′3–type composite as described by Guo et al…”

“…These two structure types are related by an in-plane shift of one of the ( M 2 Te) n layers. In our recent work, we have shown that these two types of stacking coexist in Na 2 Zn 2 TeO 6 (NZTO) . The materials with M = Zn and Mg are considered as ideal candidates for application as solid-state electrolytes.…”

Honeycomb layered oxides: structure, energy storage, transport, topology and relevant insights

“…412 Experimental and theoretical reports on the structures of these materials has already revealed some stacking disorders with honeycomb layered species such as Na 3 Ni 2 SbO 6 , Na 2 Zn 2 TeO 6 and Na 2 Ni 2 TeO 6 , associating them with emergent functionalities such as phase transitions, magnetic ground states and ionic diffusion. 60,170,253,413 Although defects have been known to have both prolific and detrimental effects on honeycomb layered oxides, they still remain vastly underexplored. Nonetheless, de novo computational and experimental techniques are expected to uncover new defect physics and chemistry that will expand their uses into multiple fields.…”

Unravelling the Fast Alkali‐Ion Dynamics in Paramagnetic Battery Materials Combined with NMR and Deep‐Potential Molecular Dynamics Simulation

“…Although the integral of Peak2 obviously increases with elevated temperature, the fractions of Peak2 are quantified as 0.41±0.03 based on VOCS spectra at variable temperatures (Figure 4 b) after taking into account the transverse relaxation effects during the echo periods [37] . Given that no transform between P 6 3 / mcm and P 6 3 22 by interlayer slipping is expected in such a narrow variable temperature range, [38] two isotropic shifts may correspond to interlayer averaged 23 Na shift of P 6 3 / mcm and P 6 3 22, respectively.…”