Abstract
In the quest for developing novel and efficient batteries, a great interest has been raised for sustainable K-based honeycomb layer oxide materials, both for their application in energy devices as well as for their fundamental material properties. A key issue in the realization of efficient batteries based on such compounds, is to understand the K-ion diffusion mechanism. However, investigation of potassium-ion (K^+) dynamics in materials using e.g. NMR and related techniques has so far been very challenging, due to its inherently weak nuclear magnetic moment, in contrast to other alkali ions such as lithium and sodium. Spin-polarised muons, having a high gyromagnetic ratio, make the muon spin rotation and relaxation (mu ^+SR) technique ideal for probing ions dynamics in these types of energy materials. Here we present a study of the low-temperature magnetic properties as well as K^+ dynamics in honeycomb layered oxide material {hbox {K}_2hbox {Ni}_2hbox {TeO}_6} using mainly the mu ^+SR technique. Our low-temperature mu ^+SR results together with complementary magnetic susceptibility measurements find an antiferromagnetic transition at T_{mathrm{N}}approx 27 K. Further {mu}^{+}SR studies performed at higher temperatures reveal that potassium ions (K^+) become mobile above 200 K and the activation energy for the diffusion process is obtained as E_{mathrm{a}}=121 (13) meV. This is the first time that K^+ dynamics in potassium-based battery materials has been measured using mu ^+SR. Assisted by high-resolution neutron diffraction, the temperature dependence of the K-ion self diffusion constant is also extracted. Finally our results also reveal that K-ion diffusion occurs predominantly at the surface of the powder particles. This opens future possibilities for potentially improving ion diffusion as well as K-ion battery device performance using nano-structuring and surface coatings of the particles.
Highlights
In the quest for developing novel and efficient batteries, a great interest has been raised for sustainable K-based honeycomb layer oxide materials, both for their application in energy devices as well as for their fundamental material properties
Our studies of low-temperature magnetism in K2Ni2TeO6 reveal that this material exhibits an AFM transition at TN ≈ 27 K and ZF-μ+SR oscillation signal suggests commensurate spin ordering down to 2 K. μ+SR studies performed on K2Ni2TeO6 at higher temperatures reveal that potassium ions (K+ ) are dynamic above 200 K (with an activation energy Ea = 121 (13) meV extracted from the experimental data), revealing for the first time that K + dynamics can be measured using μ+SR
The Rietveld fits of high-resolution neutron powder diffraction patterns was challenging due to a significant broadening observed for [h, k, l = 0] peaks
Summary
In the quest for developing novel and efficient batteries, a great interest has been raised for sustainable K-based honeycomb layer oxide materials, both for their application in energy devices as well as for their fundamental material properties. Our studies of low-temperature magnetism in K2Ni2TeO6 reveal that this material exhibits an AFM transition at TN ≈ 27 K and ZF-μ+SR oscillation signal suggests commensurate spin ordering down to 2 K. Μ+SR studies performed on K2Ni2TeO6 at higher temperatures reveal that potassium ions (K+ ) are dynamic above 200 K (with an activation energy Ea = 121 (13) meV extracted from the experimental data), revealing for the first time that K + dynamics can be measured using μ+SR.
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