Any dielectric material under a strain gradient presents flexoelectricity. Here, we synthesized 0.75 sodium bismuth titanate −0.25 strontium titanate (NBT-25ST) core–shell nanoparticles via a solid-state chemical reaction directly inside a transmission electron microscope (TEM) and observed domain-like nanoregions (DLNRs) up to an extreme temperature of 800 °C. We attribute this abnormal phenomenon to a chemically induced lattice strain gradient present in the core–shell nanoparticle. The strain gradient was generated by controlling the diffusion of strontium cations. By combining electrical biasing and temperature-dependent in situ TEM with phase field simulations, we analyzed the resulting strain gradient and local polarization distribution within a single nanoparticle. The analysis confirms that a local symmetry breaking, occurring due to a strain gradient (i.e. flexoelectricity), accounts for switchable polarization beyond the conventional temperature range of existing polar materials. We demonstrate that polar nanomaterials can be obtained through flexoelectricity at extreme temperature by tuning the cation diffusion.

@en

Transmission electron microscopy is a powerful and commonly used tool to study nanoparticles, nanowires and 2D materials. It provides static information from the sample with atomic resolution, in high vacuum and at ambient temperature. However, in real processes, the environment is often different and dynamic.

MEMS-based sample carriers became a breakthrough for in-situ TEM where they function as a micro-sized laboratory and enable dynamic studies. The Nanoreactor allows for manipulation of samples by simultaneously applying heat and gas stimuli, through which real-time studies of solid-gas interactions are enabled inside the TEM. Many challenges are still to be faced in further optimization of Nanoreactors. Especially because the tiny scale and the extreme conditions at which these devices must operate, limit the number of suitable tools to characterize and help understand their behavior.

In this project, the electro-thermo-mechanical behavior of the Nanoreactor is characterized using various microscale analytical techniques. The obtained results are used to model the Nanoreactor with finite element analysis, including electric current, mechanical stability, heat transfer, gas flow, and their interdependence. Using the acquired knowledge and the model, an optimized Nanoreactor design is proposed that improves membrane deflection, spatial sample drift, temperature homogeneity, temperature stability, gas flow speed and gas switching time.