Embedded polytypes inBi2Sr2−xLaxCuO6

Abstract

We investigate the presence of secondary phases in La-doped Bi-2201 thin films grown by laser ablation. The cation ratios in the target material, the oxygen pressure, and the substrate temperature during the deposition are the main parameters determining the presence of diluted intergrowth and/or polytype aggregates. A statistical model of random intergrowth is used to analyze the x-ray diffraction ͑XRD͒ anomalies caused by hidden defects and to characterize the latter. A detailed structural XRD refinement on oriented aggregates allows us to identify the guest phase as a Bi deficient phase, Bi-1201. The occurrence of this particular embedded polytype is accompanied by a global Bi deficiency introduced in the films by the growing process and/or by the annealing treatment. The presence of La favors the Bi-1201 formation mostly as La-rich c-axis oriented aggregates. Bi excess in the target material improves considerably the crystallographic structure of Bi-2201, avoids intergrowth formation, but does not prevent the phase separation of Bi-1201 in La-doped thin films. We also investigate the influence of the deposition parameters on the type of intergrowth as well as their variation with La doping. This work introduces a specific methodology for optimizing the growth of thin films grown by laser ablation, which applies to layered oxides that admit polytypes with close formation enthalpies in their phase diagram.

Enhanced localized superconductivity in Sr2RuO4thin film by pulsed laser deposition

“…Nevertheless, there are some asymmetries in the profiles of the (0 0 l) family of Sr 2 RuO 4 peaks in figure 1(a), which can be identified more as structural defects rather than secondary phases. These are most likely stacking faults which are known common defects in layered perovskite structures [17,18]. These asymmetries, which were also reported in other studies [19], can be de-convoluted into main peaks and shoulder peaks as shown in figure 3 A similar plot is done for the asymmetric shoulders of the superconducting Sr 2 RuO 4 film in figure 3(c); here no correlation can be observed and so the fitting does not converge as cos 2 θ/sinθ→0.…”

“…These asymmetries, which were also reported in other studies [19], can be de-convoluted into main peaks and shoulder peaks as shown in figure 3 A similar plot is done for the asymmetric shoulders of the superconducting Sr 2 RuO 4 film in figure 3(c); here no correlation can be observed and so the fitting does not converge as cos 2 θ/sinθ→0. For comparison, a very similar random variation of the c-axis versus cos 2 θ/sinθ is also seen in Bi 2 Sr 2−x La x CuO 6 , as shown in figure 3(c) [17]. An explanation of equation (2) can be found in the supplemental material.…”

“…Following the analysis in ref [17], the random deviation of the shoulder peaks suggests the existence of localized regions whose c-axis differs from the bulk of the matrix which can be interpreted as containing (0 0 l) stacking faults. The metallic film has a more chaotic c-axis versus the cos 2 θ/ sinθ profile as well as a broader rocking curve than those of the superconducting Sr 2 RuO 4 film (not shown), implying a higher level of defects.…”

Modeling of Interface and Internal Disorder Applied to XRD Analysis of Ag-Based Nano-Multilayers

“…In this section, we present and discuss the results on the Ag–Ge/AlN NMLs, based on X-ray diffraction data and their comparison with the model calculations introduced in the preceding section. For the particular case of annealed sequentially deposited samples under RF bias, to account for the observed nonmonotonous X-ray peak displacements, we used a model for random intercalation − that allows the characterization of the guest phase and the estimation of its concentration within the host matrix. Real and simulated TEM pictures are also presented for completion.…”

“…As announced in the preceding section, this is incompatible with any kind of strain because in this case the deviations would have the same sign obeying Bragg’s law. The observed anomalous deviations are typical for random intercalation of fixed length polytypes. − To find the concentration and nature of the intercalate from the measure of the peak deviations, we used the model introduced in ref in similar circumstances. In momentum space, the momentum transfer along the normal to the family of diffracting planes is .…”