Sol–gel synthesis and crystallization kinetics of dysprosium-titanate Dy2Ti2O7 for photonic applications

Abstract

We present a generic sol–gel approach for the preparation of nanocrystalline Dy2Ti2O7. This approach allows the preparation of powders and highly transparent thin films having nanocrystals of a tailored size. The thermal evolution of these nanocrystals was followed by conventional structural methods and furthermore, we determine both the kinetic parameters of the nanocrystal nucleation process from amorphous xerogel as well as the crystallization mechanism. The crystallization temperature was 798 ± 2 °C. The nanocrystal growth started by homogeneous nucleation with a constant nucleation rate followed by three dimensional growth. The activation energy of the crystallization was 780 kJ mol−1, and the energy of nanocrystal growth was 24.4 kJ mol−1. We demonstrate the existence of pure pyrochlore structure of Dy2Ti2O7 with the lattice parameter a equal to 10.2 Å. The structural evolution of nanocrystalline thin films was identical to that of the evolution of xerogels. A thin film of thickness 342 nm exhibited an optical transmission of 93.39% with a refractive index of 2.138 at 935 nm. These results provide fundamental information about the crystallization behavior of Dy2Ti2O7: they can be used to prepare pure nanocrystalline xerogels and highly transparent thin films with tailored structural properties which are suitable for photonic applications.