Functional properties of transition-metal oxides strongly depend on crystallographic defects; crystallographic lattice deviations can affect ionic diffusion and adsorbate binding energies. Scanning x-ray nanodiffraction enables imaging of local structural distortions across an extended spatial region of thin samples. Yet, localized lattice distortions remain challenging to detect and localize using nanodiffraction, due to their weak diffuse scattering. Here, we apply an unsupervised machine learning clustering algorithm to isolate the low-intensity diffuse scattering in as-grown and alkaline-treated thin epitaxially strained SrIrO3 films. We pinpoint the defect locations, find additional strain variation in the morphology of electrochemically cycled SrIrO3, and interpret the defect type by analyzing the diffraction profile through clustering. Our findings demonstrate the use of a machine learning clustering algorithm for identifying and characterizing hard-to-find crystallographic defects in thin films of electrocatalysts and highlight the potential to study electrochemical reactions at defect sites in operando experiments.
All-solid-state lithium batteries promise significant improvements in energy density and safety over traditional liquid electrolyte batteries. The Al-doped AlxLi7-3xLa3Zr2O12 (LLZO) solid-state electrolyte shows excellent potential given its high ionic conductivity and good thermal, chemical, and electrochemical stability. Nevertheless, further improvements on LLZO's electrochemical and mechanical properties call for an incisive understanding of its local microstructure. Here, we employ Bragg Coherent Diffractive Imaging to investigate the atomic displacements inside single grains of LLZO with various Al-doping concentrations, resulting in cubic, tetragonal, and cubic-tetragonal mixed structures. We observe coexisting domains of different crystallographic orientations in the tetragonal structure. We further show that Al doping leads to crystal defects such as dislocations and phase boundary in the mixed-and cubic-phase grain. This study addresses the effect of Aldoping on the nanoscale structure within individual grains of LLZO, which is informative for the future development of solid-state batteries.
experience multiple types of phase transitions that hinder electrochemical performance. Phase transitions due to sodium-ion ordering have been linked to slower diffusion of sodium ions. [7,8] The notorious P2-O2 structural phase transition, in which the sodium-ion sites change from prismatic to octahedral coordination combines two mechanisms that cause significant material degradation leading to poor cycle life. [9] The sliding of transition metal layers during the P2-O2 phase transition leads to layer exfoliation after many cycles, [10,11] while the significant volume change (>20%) contributes to further structural degradation during cycling. [9,[11][12][13] Full understanding of the mechanisms behind P2-type Na x TMO 2 phase behavior remains elusive and is critical to designing durable sodium-ion batteries. [14] In practical and functional batteries, nanoparticulates of active cathode material are surrounded by other cell components, necessitating the development of characterization techniques that can interrogate multicomponent systems. X-rays have the penetrating power that allows for operando characterization in a fully functioning cell, and X-ray powder diffraction has been used extensively to study positive electrode materials in situ. [11,[15][16][17][18] For example, in situ powder diffraction of P2-type Na x TMO 2 has shown the formation of stacking faults during the P2-O2 phase transition. [11] Ex situ X-ray powder diffraction revealed superstructure peaks corresponding to discrete Na + to Na + distances in sodium-ion ordering phases. [7] Despite its Structural and ion-ordering phase transitions limit the viability of sodium-ion intercalation materials in grid scale battery storage by reducing their lifetime. However, the combination of phenomena in nanoparticulate electrodes creates complex behavior that is difficult to investigate, especially on the single-nanoparticle scale under operating conditions. In this work, operando single-particle X-ray diffraction (oSP-XRD) is used to observe singleparticle rotation, interlayer spacing, and layer misorientation in a functional sodium-ion battery. oSP-XRD is applied to Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 , an archetypal P2-type sodium-ion-positive electrode material with the notorious P2-O2 phase transition induced by sodium (de)intercalation. It is found that during sodium extraction, the misorientation of crystalline layers inside individual particles increases before the layers suddenly align just prior to the P2-O2 transition. The increase in the long-range order coincides with an additional voltage plateau signifying a phase transition prior to the P2-O2 transition. To explain the layer alignment, a model for the phase evolution is proposed that includes a transition from localized to correlated Jahn-Teller distortions. The model is anticipated to guide further characterization and engineering of sodium-ion intercalation materials with P2-O2 type transitions. oSP-XRD, therefore, opens a powerful avenue for revealing complex phase behavior in heterogeneous nanop...
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