SYNTHESIS AND DIELECTRIC-PROPERTIES OF SUBSTITUTED LANTHANUM ALUMINATE

LaAlO3 was chemically modified in order to ascertain the effects of su bstitution of larger cations on the compound's slight rhombohedral dis tortion from cubic symmetry-a property that often degrades the perform ance of LaAlO3 substrates for epitaxial high-temperature superconducti ng films. La1-xSrxAl1-xTixO3 (x = 0.05, 0.10, 0.15, 0.25), La1-xSrxAl1 -xZr(x)O(3), La1-xSrxAl1-xMgxO3-2xF2x, and La1-xSrxAl1-xScxO3-xFx (x = 0.05, 0.10, 0.15) were prepared in polycrystalline form and 1-2 mm si ngle crystals of the Sr,Ti- and Sr,Zr-substituted systems were grown u sing a PbO-PbF2-B2O3-PbO2 flux. Shifts in the peak positions of the X- ray powder diffraction patterns confirmed substitution of the larger c ations. The diffraction patterns were also typified by line-broadening and a decrease in the rhombohedral splitting at all doping levels. Th e dielectric constant of LaAlO3 was unchanged for all of the fluoride- containing systems and for the 5% Sr,Ti- and Sr,Zr-systems.