Tuning of superdiamagnetism in La2CuO4 by solid-state electrochemical fluorination and defluorination

Sami Vasala,Oliver Clemens,Lambert Alff

doi:10.1063/5.0040997

Sami Vasala, Oliver Clemens + Show 1 more

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https://doi.org/10.1063/5.0040997

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Abstract

Here, we demonstrate the electrochemical fluorination of La2CuO4 in an all-solid-state cell. This method of fluorine intercalation is controllable and reproducible, offering a precise adjustment of hole doping and thus tuning of superdiamagnetic (i.e., the perfect diamagnetic behavior of a superconductor) properties. The fluorinated La2CuO4Fx samples showed an increase in Tc and in diamagnetic response with increasing fluorine content with x up to ∼0.2. The fluorination process could also be reversed, as fluorine could be electrochemically deintercalated from La2CuO4Fx under re-formation of the antiferromagnetic insulator La2CuO4, returning the samples to a non-superdiamagnetic state. This method offers a convenient way of studying the detailed effects of hole doping in La2CuO4 and shows that tuning of material properties by electrochemical fluorination can also be extended to the field of superconductors.

Highlights

Voltage control for the switching and tuning of functional properties such as magnetism1 and optical properties2,3 as well as superconductivity4 is a current hot-topic in materials research
La2CuO4 was electrochemically modified in an all-solid-state cell; the degree of electrochemically oxidative change, most plausibly an electrochemical oxidative fluorination, was found to be controllable, and the results were reproducible between separate cells. This method offers a precise adjustment of hole doping in La2CuO4 and tuning of superdiamagnetic properties with x up to at least ∼0.20, above which side reactions due to the fluorination of the carbon additive used in the cathode composite began to interfere with the process
The fluorination process could be reversed, as fluorine could be deintercalated from La2CuO4Fx, returning the samples to a non-superdiamagnetic state

Summary

Introduction

Voltage control for the switching and tuning of functional properties such as magnetism and optical properties as well as superconductivity is a current hot-topic in materials research. Such voltage control can be achieved via liquid- or solid-state systems and can be based on charge doping via double layers or the intercalation of ionic species, introducing holes or electrons into the structure, which are of keen relevance for the properties detailed above. Solid ion conductors have an advantage in having a transport number of t ∼ 1 for a single ionic species, facilitating a clear reaction chemistry at the solid to solid interface. We have previously investigated the use of fluoride ions, a charge carrier with high electrochemical stability and high ionic mobility in solid-state devices, in order to switch functional properties, a concept not considered for superconductors in large detail

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