Lanthanum gallate substrates for epitaxial high-temperature superconducting thin films

Abstract

We demonstrate that lanthanum gallate (LaGaO3) has considerable potential as an electronic substrate material for high-temperature superconducting films. It provides a good lattice and thermal expansion match to YBa2Cu3O7−x, can be grown in large crystal sizes, is compatible with high-temperature film processing, and has a reasonably low dielectric constant (ε≂25) and low dielectric losses. Epitaxial YBa2Cu3O7−x films grown on LaGaO3 single-crystal substrates by three techniques have zero resistance between 87 and 91 K.

Twinning structure of LaGaO3 grown by the Czochralski method

“…LaGaO3 has orthorhombic structure with lattice constants a --0.5487 nm, b = 0.520 nm, c = 0.7752 nm [4] at room temperature. The lattice constants given by several authors show small differences and the average values given by Sandrom et al [5] are a = 0.5519 nm, b = 0.5494 nm and c = 0.7777 nm. These discrepancies in the lattice constants can be caused by the observed twinning structure.…”

“…It should be mentioned that from the known orthogallates, LnGaO3 (Ln= La-Gd), only LaGaO3 [6,11] and NdGaO 3 [11] melt congruently, and the Czochralski technique was used to grow single-crystal NdGaO3 [11,12] and LaGaO 3 [5,[13][14][15].…”

Defects in Detwinned LaGaO3Substrates

“…Lanthanum, neodymium and praseodymium gallates [1,2] have often been expected as substrate materials for HTSC epí-taxy mainly because of their attractive dielectric properties (low ε and tan δ) and low lattice mismatches, both at deposition and application temperatures. The most crucial problem in application of these materials as substrates for the epitaxy is the existence of the structural phase transitions [3] leading to the twinning and surface roughening [4].…”

Development and Dielectric Properties of Ba2−xSrxDyTaO6(x=0, 1, and 2) Substrates for YBa2Cu3O7−δFilms

“…The substrate plays an important role in the development of high-quality superconducting films. Many compounds such as SrTiO (5,6), ZrO (7), REGaO (8,9), MgO (10), and LaAlO (11) are in use as substrates for YBCO films. Recently, some chemically nonreactive ceramics such as Ba DySnO (12), Ba LaNbO (13), and Ba \V Sr V DySbO (14) were reported to possess excellent qualities of an ideal substrate for YBCO films.…”