Solid-State Reactions Occurring during the Synthesis of CaTiO3-NdAlO3 Perovskite Solid Solutions

The X-ray powder-diffraction technique was used to investigate the solid-state reaction paths to the 0.7CaTiO3-0.3NdAlO3 perovskite solid solution. The results show that the perovskite phases CaTiO3 and NdAlO3 are formed prior to the solid solution, regardless of the combination of oxide powders used as reagents. The two perovskites subsequently react to form a solid solution at temperatures above 1200 C. The reaction between CaTiO3 and NdAlO3 was studied using a diffusion couple, which revealed that the slower kinetics of incorporation of the Al into the forming solid solution results in the formation of an intermediate phase based on hexaluminate CaAl12O19. The presence of such inclusions results in the formation of defects in the perovskite matrix phase, which adversely affects the dielectric losses of the sintered ceramics based on the 0.7CaTiO3-0.3NdAlO3 solid solution. To minimize the concentration of CaAl12O19-based inclusions, a thorough calcination procedure with intermediate homogenizations needs to be conducted at temperatures above 1300 C.