Atomic-scale identification of novel planar defect phases in heteroepitaxial YBa2Cu3O7−δ thin films

Abstract

We have discovered two novel types of planar defects that appear in heteroepitaxial YBa 2 Cu 3 O 7−δ (YBCO123) thin films, grown by pulsed-laser deposition (PLD) either with or without a La 2/3 Ca 1/3 MnO 3 (LCMO) overlayer, using the combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and electron energy loss spectroscopy (EELS) mapping for unambiguous identification. These planar lattice defects are based on the intergrowth of either a BaO plane between two CuO chains or multiple Y-O layers between two CuO 2 planes, resulting in non-stoichiometric layer sequences that could directly impact the high-T c superconductivity.Recently, a great deal of interest has been focused on thin-film heterostructures comprising YBa 2 Cu 3 O 7−δ (YBCO123) and other complex oxides, because of novel interfacial interactions 1-3 that could affect the highcritical temperature (T c ) superconductivity. 4,5 YBCO123 in heteroepitaxial form is known to contain a variety of crystalline defects, as its layered perovskite structure is sensitive to lattice strains induced by the epitaxial mismatch. [6][7][8][9][10][11] Since such defects may also affect the microscopic pairing mechanism, it is important to determine their lattice structures at the atomic scale. There is solid experimental evidence to suggest that the interfacial lattice mismatch in heteroepitaxial thin films of complex oxides can, through induced lattice strains, affect the microstructure in the film.In an earlier study of YBCO123 thin films heterostructured with La 2/3 Ca 1/3 MnO 3 (LCMO) overlayers, we observed nanoscale domains of YBCO124 and YBCO247 containing CuO-chain intergrowths, which were attributed to the heteroepitaxial strain and also shown to cause attenuation of T c . 7 In the present study, we focus on defect phases associated with Ba-O and Y-O intergrowths in heteroepitaxial YBCO123 thin films both with and without LCMO overlayers. Two novel types of planar defects are unequivocally observed, both deviating from the normal stacking sequence (CuO-BaO-CuO 2 -Y-CuO 2 -BaO) of the YBCO123 lattice. The first defect type (henceforth called type D1) consists of a BaO layer sandwiched between two CuO-chain layers. The second defect type consists of the addition of either one (type D2) or two (type D2') extra Y-O layers between the CuO 2 planes.The samples used in this study include single-layer YBCO123 and bi-layer LCMO/YBCO123 thin films.

The Route to Supercurrent Transparent Ferromagnetic Barriers in Superconducting Matrix

“…43 It is known that in the composite films, the concentration of these defects is usually much higher. 42,44,45 It is in agreement with our observation. The introduction of the LCMO layer in between YBCO layers could be a reason for the larger density of the intergrowths in the top YBCO layer.…”

Solid-State Electrochemical Switch of Superconductor–Metal–Insulators

“…A layered crystal structure of YBa 2 Cu 3 O 7−δ films is clearly visualized together with an ∼10 nm-thick GDC/YSZ substrate in both samples (Figure 4a,c). Similar to previous observations of oxidized YBCO films, 20,21 many planar defects are also detected in the HAADF-STEM image of sample D. The crystal lattices of sample H (Figure 4b) and sample D (Figure 4d) agree well with the crystal structure models of YBa 2 Cu 3 O 6 and YBa 2 Cu 3 O 7 (Figure 1a). Thus, the similar crystal structures of YBa 2 Cu 3 O 6 and YBa 2 Cu 3 O 7 allow δ to be modulated by solid-state electrochemical redox treatments.…”

New insight into strain and composition of BaZrO3 nanorods in REBCO superconductor

“…We have reported earlier that the same metric, (Ba + Zr)/Cu, has a considerable effect on c-axis lattice mismatch between BZO and REBCO [48,61,63]. Multiple studies have reported presence of dense arrays of REBCO 124/248 type, 223 and other stacking faults [54,[83][84][85][86][87][88][89][90][91], and we have regularly observed the same features, as can also be seen in figure 2(d). One can readily envision a mismatch strain accommodation between c-axis of BZO and REBCO by inserting extra Cu-O planes to form 124-type defect at regular intervals in REBCO matrix to minimize mismatch between REBCO and BZO along the c-axis.…”