Tailoring the structural, optical and electrical properties of perovskite nickelates through the Sm content variation in Nd1-xSmxNiO3 thin films for solar thermal applications

Rare-earth nickelates (RNiO₃) are indispensable materials for innovative applications requiring property changes at specific temperatures. This study introduces a novel approach for fabricating large-scale Nd_1-xSm_xNiO₃ thin films through sputtering and subsequent air annealing, bypassing the need for extreme oxygen pressures typically required to stabilize the metastable Ni³⁺ oxidation state. Precise control over the chemical composition enables fine-tuning of structural distortions, leading to tailored physical properties, including transition temperatures. X-ray diffraction analysis confirms the perovskite structure, with a linear correlation between lattice parameters and Nd-Sm composition. Advanced characterization techniques including transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy-loss spectroscopy, provide detailed insights into the microstructure and oxidation states, while Fourier-transform infrared spectroscopy and electrical measurements reveal a metal-insulator transition (MIT) and thermochromic behavior. The metal-insulator transition temperature (T_MI) ranges from 61 to 78 °C, corresponding to Sm content variations from 0.70 to 0.80 in Nd_1-xSm_xNiO₃ thin films. Spectroscopic ellipsometry further demonstrates phase transitions in dielectric properties, which is essential for optoelectronic applications. Lastly, the Nd_0.20Sm_0.80NiO₃ thin film shows potential as a selective layer for solar thermal applications. By employing air annealing instead of high-pressure oxygen annealing at 200 bars, this approach now enables deposition on surfaces as large as a square meter, paving the way for designing smart materials with tailored functionalities.