The bulk densities were measured by

The bulk densities were measured by Archimedes’ method. The data together with the calculated theoretical density from rule of mixtures (ROM by taking the Rietveld volume fractions) value were used to find out the final relative densities. X-ray diffraction measurements were performed on a Rigaku D-Max III (Tokyo, Japan) instrument operating in Bragg-Brentano geometry and equipped with a Copper anode X-Ray source (Cukα = 1.5406 Å at 40 kV, 30 mA), diffracted beam graphite monochromator, 1° divergence and receiving slit and 5° diffracted beam Soller slits. Scans were performed over the 5°-135° (2ϴ) range, with a 0.02° step size and 2 s counting time per step. Instrumental broadening was characterized by means of an Y2O3 powder (99.99%, Sigma-Aldrich, CAS# 1314-36-9) annealed at 1400°C for 24 hours. The morphological properties and microstructure were analyzed by using a scanning electron microscope (SEM, FEI, Quanta 250 FEG, USA) and a transmission electron microscopy (TEM, ThermoFisher Talos F200S FEG, Netherlands) operating at 200 kV. Prior to SEM analysis all the samples were coated by sputter coating. TEM sample was prepared suspending a small amount of powder in ethanol, performing a 5 mins sonication treatment and putting 50 µL of solution on a TEM copper grid covered by amorphous carbon.