Synthesis and Dielectric Properties of Subsituted Lanthanum Aluminate

Abstract

LaAlO 3 was chemically modified in order to ascertain the effects of substitution of larger cations on the compound's slight rhombohedral distortion from cubic symmetry—a property that often degrades the performance of LaAlO 3 substrates for epitaxial high‐temperature superconducting films. La 1– x Sr x Al 1– x Ti x O 3 (x = 0–05, 0.10, 0.15, 0.25),La 1– x Sr x Al 1–x Zr x O 3 , La 1– x Sr x Al 1–x Mg x O 3–2x F 2x and La 1– x ,Sr x Al 1– x Sc x O 3– x (x = 0.05, 0.10, 0.15) were prepared in polycrystalline form and 1–2 mm single crystals of the Sr,Ti‐ and Sr,Zr‐substituted systems were grown using a PbO–PbF 2 –B 2 O 3 –PbO 2 flux. Shifts in the peak positions of the X‐ray powder diffraction patterns confirmed subsitution of the larger cations. The diffraction patterns were also typified by the line‐broadening and the decrease in the rhombohedral splitting at all doping levels. The dielectric constant of LaAlO 3 was unchanged for all of the fluoride‐containing systems and for the 5% Sr, Ti‐ and Sr,Zr‐systems.