The thermal expansion for the perovskite (La,Sr)(Al,Ta)O3, i.e., LSAT, grown from the formulation 0.29(LaAlO3):0.35(Sr2AlTaO6), was determined by Rietveld refinement of neutron powder diffraction data over the temperature range of 15–1200 K. In comparison to LaAlO3 the relative volume thermal expansion is the same, although the cell volume of LSAT is slightly larger. Site occupation refinement for LSAT gives a structural formula of (La0.29(5)Sr0.71(5))A site(Al0.65(1)Ta0.35(1))B siteO3. At and below 150 K, LSAT shows a small distortion from cubic symmetry. Unlike the cubic-to-rhombohedral transition (800 K) observed in LaAlO3, the low temperature structural phase transition in LSAT appears to be cubic-to-tetragonal or cubic-to-orthorhombic. The rms displacement of the A site in LSAT is significantly larger than that for LaAlO3, and about half of the difference can be accounted for by a static displacement component.

A perovskite-like single-crystal substrate material has been investigated that simultaneously permits epitaxial growth of 1-2-3 superconductor films and possesses desirable rf properties of low dielectric constant and loss tangent. The lattice constant of 3.792 Å provides a lattice match to within 1% of the a axis of 1-2-3. Sputtered films of erbium-barium-copper-oxide have been produced on (100) LaAlO3 substrates that exhibit sharp resistive transitions at 90 K (ΔT=1K), bulk superconductivity as determined by ac susceptibility measurements, and nearly single-crystal growth as evidenced by x-ray diffraction and high-resolution scanning electron microscopy. The high-frequency dielectric properties of LaAlO3 were experimentally investigated at several temperatures. The low-frequency dielectric constant was measured to be 15 and the microwave loss tangent ranged from 6×10−4 at room temperature to 5×10−6 at 4 K.

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