Effect microwave sintering in enhancing the infrared transmittance properties of combustion synthesized nanostructured Y2O3 ceramics comprising La3+ ion in the matrix

Synthesis of nano particles of La³⁺ ion subsituted Y2O3 ceramics (∼16nm) by a single step auto-igniting combustion technique, followed by microwave sintering to optimum density, and their remarkable infrared transmission characteristics are presented in this paper. The XRD pattern of the as prepared sample clearly indicates that the La³⁺ ions are effectively replacing Y³⁺ ions in the yttria cubic structure and it matches very well with the JCPDS file no-89-5591. As the percentage of La³⁺ increases a slight increase in lattice parameter was observed. The size of the crystallites were calculated using Scherrer formula and they found to be in the size range of 10-20 nm and the average size of the crystallites was 16 nm. The phase purity and nano nature of the crystallites were confirmed using HRTEM. The UV-Visible and FTIR spectroscopy were effectively used to characterise the powder and to obtain the transmittance properties of the sintered samples. The pellets with green density 52% of the theoretical density were sintered using a microwave furnace. The pellets achieved 99% of the theoretical density at 1520°C for a soaking duration of 20 minutes. The pellets were translucent and the SEM analysis revealed that they were well sintered with reduced average grain size of ∼430nm. The pellet showed an enhanced transmittance of 77% in the UV-Visible region and 72% in the mid infrared region. The transmittance properties shown by the pellets are superior to those in the case of pure Y2O3 and is due to the superior powder quality and the fast uniform densification via microwave sintering. Microwave assisted sintering of the combustion synthesized powder is therefore a promising fabrication technique, especially for infrared transparent ceramics, which considerably reduces the sintering temperature, soaking duration, the grain size and enhances the transmittance properties.