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 0.7CaTiO 3 −0.3NdAlO 3 perovskite solid solution. The results show that the perovskite phases CaTiO 3 and NdAlO 3 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 CaTiO 3 and NdAlO 3 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 CaAl 12 O 19 . 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 0.7CaTiO 3 −0.3NdAlO 3 solid solution. To minimize the concentration of CaAl 12 O 19 -based inclusions, a thorough calcination procedure with intermediate homogenizations needs to be conducted at temperatures above 1300 °C.