Effect of capping ligands on the synthesis and on the physical properties of the nanoparticle of LiTaO₃

Abstract

This paper reports the synthesis of lithium tantalate (LiTaO₃) nanoparticles by a sol-gel process involving the use of capping ligands. When the sol was allowed to form gel and then annealed at 600 °C for 1 h in the presence of oxygen, hexagonal crystallites of size 2-5 µm were formed. But when the sol was heat treated at 600 °C for 1 h in the presence of oxygen before gelation, agglomerated nanoparticles were formed. The addition of aniline before gelation (a neutral capping ligand with N-donor atom) not only restricted gelation, but also helped in the formation of well-separated and irregular nanoparticles of sizes 40-70 nm, which was confirmed from TEM and XRD studies. The anionic-ligand oleic acid (lipophilic ligand with O-donor atoms) restricted gelation by arresting the surface of LiTaO₃, and spherical nanoparticles of size 20-40 nm were formed after heating the sol. Comparison of ferroelectric and dielectric properties between bulk particle and spherical nanoparticles (obtained using oleic acid) are reported by characterizing these particles using Raman spectroscopy and differential scanning calorimetry (DSC). The Curie temperature decreases with decreasing the particle size of LiTaO₃.