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English: This study reports on the second harmonic generation (SHG) of barium titanate (BaTiO3) nanoparticles synthesized by a low-cost and easily-accessible sol-gel hydrothermal method at different temperatures (100-250 °C). According to the powder X-ray diffraction (XRD) pattern, all of the prepared samples had meta-phase without a centre of symmetry, and the crystal structure changes from simple cubic to rhombohedral at different temperatures. In addition to XRD, differential scanning calorimetry (DSC) confirms the meta-phase in BaTiO3 by showing a significant phase shift indicating structural distortion. The variation in particle size was observed from transmission electron microscope (TEM) images and the selected area electron diffraction (SAED) pattern as well supports the presence of structural distortion in the nanomaterials. The phase variation in BaTiO3 has not only affected its structure but also creates a disorder in its magnetic properties by changing it from paramagnetic to ferromagnetic for different synthesizing temperatures. This was determined with a vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR) techniques. As a consequence of this structural deformation, particle size variation, and magnetic phase transition the second harmonic generation (SHG) conversion efficiency of BaTiO3 has been improved. Hence this technique for synthesizing nanomaterials could be a promising candidate for fabricating bio-compatible imaging probes and coherent bio-markers in the field of medicine and electronics. S. Mahalakshmi, Jeyanthinath Mayandi, Suresh Sagadevan, V. Ragavendran, K. Manikandan, S. Arumugam, J.M. Pearce, V. Venkatachalapathy,Enriched second-harmonic generation in meta-phase barium titanate nanostructures synthesized by sol-gel hydrothermal method. Journal of Alloys and Compounds,2022,936, 168171, https://doi.org/10.1016/j.jallcom.2022.168171. Academia open access preprint