Dynamically preferred state with strong electronic fluctuations from electrochemical synthesis of sodium manganate

Electrochemical (de)intercalation is a delicate method to precisely control the alkaline ion composition in alkaline transition metal oxides. Because of complicated interactions, metal charge ordering patterns can form spontaneously at special fractional alkaline compositions and orderings. Here, we show that this elegant electrochemical process can create dynamically preferred structures in an anharmonic energy landscape that conventional syntheses and computations can rarely visit. Specifically, electrochemically prepared Na1/2MnO2 ordering exhibits abnormal structure distortions, charge orderings, and dynamical activities. Strong magnetic fluctuations and lattice dynamics are observed in an unusually wide temperature range in Na1/2MnO2, which distinguishes it from all other NaxMnO2 at higher or lower Na compositions. The results emphasize the unique opportunity of using electrochemical processes to design and create novel quantum states with strongly coupled and mutually enhanced electronic and lattice fluctuations, likely through a special dynamic charge flux functional, as suggested by our computational investigations. [Display omitted] •Na1/2MnO2 shows strong magnetic fluctuations and anharmonic phonons in experiments•DFT, XRD, Raman, and neutron reveal a unique dynamic metastable phase•Magnetic and phonon dynamics are linked by charge fluxes in Na1/2MnO2 Sodium (Na)-ordering phases can form spontaneously at special sodium compositions in layered sodium transition metal oxides in Na-ion batteries. Strong electronic correlation phenomena can emerge from these phases, including unconventional superconductivity, metal-insulator transition near room temperature, and an enhanced thermoelectric effect. Our study of Na1/2MnO2, an Na-ordering, dynamically metastable phase, reveals an unusually strong magnetic fluctuation that is robust against temperature increase up to room temperature. The underlying novel mechanism of strongly coupled lattice and spin oscillations mediated through the unique charge flux oscillation prompts a new way to think about how lattice dynamics can contribute to spin fluctuations. This may also provide a new perspective to understand other strongly correlated materials, including unconventional superconductors and other energy conversion and storage materials. Electrochemical (de)intercalation is a delicate method to precisely control the composition and possible orderings of alkaline ions in alkaline transition metal oxides. Elect