Structure sequence in the CaTiO3-LaAlO3 microwave ceramics -: Revised

The composition-induced crystal structure transformations in the (1-x)CaTiO3-xLaAlO(3) microwave ceramics were studied by X-ray powder diffraction. Increasing LaAlO3 content results in two-phase transitions: Pnma -> Imma (0.4 < x < 0.5) and Imma -> R (3) over barc (0.5 < x < 0.6), which are related to changes of the octahedral tilting: a(-)b(+)a(-)-> a(-)b(0)a(-) and a(-)b(0)a(-)-> a(-)a(-)a(-), respectively. The compositional variation of the parameters of the primitive perovskite unit cell is consistent with a continuous character of the Pnma -> Imma phase transition. In the case of the Imma -> R (3) over barc crossover, a discontinuity in the variation is observed.