Recently, we reported that incorporating thin Ca_0.3Y_0.7Ba₂Cu₃O_7-x spacer layers in BaZrO₃/ YBa₂Cu₃O_7-x (BZO/YBCO) films in multilayers (ML) could lead to a coherent BZO/YBCO interface due to reduced lattice mismatch of ∼1.4% and hence improved pinning by the BZO 1D artificial pinning centers (BZO 1D-APCs). It was hypothesized that the highly strained YBCO columns around the BZO 1D-APCs due to the larger lattice constant of BZO than YBCO's in c-axis by 7.7% provide channels to facilitate Ca diffusion more preferably near the BZO/YBCO interface, leading to an enlarged YBCO's c-axis lattice constant as a consequence of the Ca/Cu substitution on the YBCO's Cu-O planes. Confirmation of this hypothesis is hence important to understand the mechanism of Ca diffusion in BZO/YBCO ML films for further enhancement of pinning efficiency of the BZO 1D-APCs. Motivated by this, this work presents a comparative study of two sets of BZO/YBCO ML films: singly-doped (SD-ML, BZO only) and the doubly-doped (DD-ML, BZO + Y₂O₃). The modulated strain field in the SD-ML films is in contrast to the non-modulated strain in the DD-ML samples as confirmed by transmission electron microscopy. Interestingly, improved pinning by >four times of the reference SD single-layer (SD-SL) film’ was observed in the SD-ML samples even when the constituent BZO/YBCO layer thickness was varied between 50-100 nm, indicating that the Ca diffusion along the strained BZO/YBCO interface and the Ca/Cu substitution on YBCO's Cu-O planes indeed correlate with the modulated strain field. In contrast, pinning degrades by >twice in DD-ML samples with respect to their DD-SL counterpart's. This result therefore suggests that strained BZO/YBCO interfaces serve as channels for Ca diffusion in SD-ML, which leads to the coherent BZO/YBCO interfaces and hence improved pinning of BZO 1D-APCs. This effect diminishes when such a modulated strain field is removed in the DD-ML samples.

最近，我们报道了在 BaZrO ₃ / YBa ₂ Cu ₃ O _{7-x中加入薄的 Ca 0.3} Y _0.7 Ba ₂ Cu ₃ O _7-x间隔层多层 (ML) 中的 (BZO/YBCO) 薄膜可导致相干 BZO/YBCO 界面，因为晶格失配降低至 1.4%，因此 BZO 1D 人工钉扎中心 (BZO 1D-APC) 的钉扎得到改善。据推测，由于 BZO 的晶格常数比 YBCO 在 c 轴上的晶格常数大 7.7%，因此 BZO 1D-APC 周围的高应变 YBCO 柱提供了促进 Ca 扩散的通道，更优选地靠近 BZO/YBCO 界面，导致由于 YBCO 的 Cu-O 平面上的 Ca / Cu 取代，扩大了 YBCO 的 c 轴晶格常数。因此，证实这一假设对于理解 BZO/YBCO ML 薄膜中 Ca 扩散的机制对于进一步提高 BZO 1D-APC 的钉扎效率非常重要。受此启发，这项工作对两组 BZO/YBCO ML 薄膜进行了比较研究：₂ O ₃）。SD-ML 薄膜中的调制应变场与透射电子显微镜证实的 DD-ML 样品中的未调制应变形成对比。有趣的是，即使当 BZO/YBCO 的组成层厚度在 50-100 nm 之间变化时，在 SD-ML 样品中也观察到了大于参考 SD 单层 (SD-SL) 膜的四倍以上的改进钉扎，这表明沿应变 BZO/YBCO 界面的 Ca 扩散和 YBCO 的 Cu-O 平面上的 Ca/Cu 取代确实与调制的应变场相关。相比之下，在 DD-ML 样本中，钉扎相对于 DD-SL 对应样本的降级 > 两倍。因此，该结果表明，应变 BZO/YBCO 界面可作为 SD-ML 中 Ca 扩散的通道，从而导致 BZO/YBCO 界面相干，从而改善 BZO 1D-APC 的钉扎。