Novel amorphous precursor densification to transparent Nd:Y2O3 Ceramics

A novel approach of neodymium ion doped yttrium oxide (Nd:Y2O3) amorphous precursor compaction and sintering is being reported for the first time. Precursor of 2 at.% Nd3+ doped Y2O3 was synthesized by gelation of sol of yttrium and neodymium nitrates with l-alanine at 80 °C for 16 h followed by gel combustion in microwave. A part of microwave precursor was heat treated at 700 °C for 5 h to give the partially crystalline Nd:Y2O3 amorphous precursor. Thermogravimetric analysis (TGA) of partially crystalline amorphous precursor of Nd:Y2O3 gave 8.5% total weight loss indicating removal of maximum organics. X-Ray diffraction (XRD) showed broad peaks indicating incomplete crystallization of cubic Nd:Y2O3. Morphology was found to be close to spherical with particles in size range 17–19 nm by TEM. Another part of microwave precursor on calcination at 1000 °C for 3 h led to formation of fully crystalline Nd:Y2O3 with particles in size range of 35–85 nm. Both partially crystalline amorphous precursor and fully crystalline Nd:Y2O3 were compacted at 400 MPa by cold isostatic press and sintered at 1750 °C for 10 h under vacuum (10−5 mbar). The partially crystalline Nd:Y2O3 amorphous precursor densified to 99% with 65% transmission at 2500 nm (0.5 mm thickness) compared to 96% densification with 34% transmission for fully crystalline Nd:Y2O3 without any sintering aids. Retention of cubic phase purity of Y2O3 was observed in both the ceramic pellets post sintering by XRD. Good grain fusion with grain growth to ≤2 μm was observed by scanning electron microscope (SEM) for partially crystalline Nd:Y2O3 amorphous precursor. Thus partially crystalline Nd:Y2O3 amorphous precursor nanopowders, with homogeneous close to spherical fine particles and high reactivity due to ionic mobility of amorphous phase, led to better densification.