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Controlling phase transitions in transition metal oxides remains a central feature of both technological and fundamental scientific relevance. A well-known example is the metal–insulator transition, which has been shown to be highly controllable. However, the length scale over which these phases can be established is not yet well understood. To gain insight into this issue, we atomically engineered an artificially phase-separated system through fabricating epitaxial superlattices that consist of SmNiO 3 and NdNiO 3 , two materials that undergo a metal-to-insulator transition at different temperatures. We demonstrate that the length scale of the interfacial coupling between metal and insulator phases is determined by balancing the energy cost of the boundary between a metal and an insulator and the bulk phase energies. Notably, we show that the length scale of this effect exceeds that of the physical coupling of structural motifs, which introduces a new framework for interface-engineering properties at temperatures against the bulk energetics. The characteristic length scale and mechanism of the metal–insulator transition in nickelate superlattices is addressed, with implications for the design of oxide electronics.

Solution deposited YBa 2 Cu 3 O 7−x (YBCO) nanocomposites with preformed nanoparticles represent a promising cost-effective approach for superior critical current properties under applied magnetic fields. Nonetheless, the majority of YBCO nanocomposites with high nanoparticle loads (>20%) suffer from nanoparticle coalescence and degraded superconducting properties. Here, we study the influence of nanoparticle concentration (0–25% mol), size (5 nm–10 nm) and composition (BaHfO 3 , BaZrO 3 ) on the generation of structural defects in the epitaxial YBCO matrix, key parameter for vortex pinning. We demonstrate that flash-heated superconducting nanocomposites with 20 mol% preformed BaHfO 3 or BaZrO 3 perovskite secondary phases feature discrete and small (7 nm) nanoparticles and high density of YBa 2 Cu 4 O 8 (Y248) intergrowths. We identify a synergy between Y248 intergrowth density and small nanoparticles to increase artificial vortex pinning centers. Also, we validate the multideposition process to successfully increase film thickness of epitaxial nanocomposites with competitive critical currents I c at 77 K.

The magnetic flux pinning capabilities of YBa 2 Cu 3 O 7-x (YBCO) coated conductors vary strongly across different regions of the magnetic field–temperature phase diagram and with the orientation of the magnetic field θ . Here, we determine the optimal pinning landscape for a given region of the phase diagram by investigating the critical current density J c ( H , θ , T ) in the 5–77 K temperature range, from self-field to high magnetic fields of 35 T. Our systematic analysis reveals promising routes for artificially engineering YBCO coated conductors in any region of interest of the phase diagram. In solution-derived nanocomposites, we identify the relevance of coexisting high amounts of short stacking faults, Cu-O vacancy clusters, and segmentation of twin boundaries, in combination with nanoparticles, for enhanced pinning performance at high magnetic fields and low temperatures. Moreover, we demonstrate that twin boundaries preserve a high pinning energy in thick YBCO films, which is beneficial for the pinning performance at high magnetic fields and high temperatures. Optimizing the microstructure of YBa 2 Cu 3 O 7-x coated conductors across the magnetic field–temperature phase diagram is important for strengthening vortex pinning and thereby enhancing the critical current. Here, a systematic microstructural investigation identifies the most relevant vortex pinning contributions in a broad range of temperatures and magnetic fields.

Solution deposited YBa Cu O (YBCO) nanocomposites with preformed nanoparticles represent a promising cost-effective approach for superior critical current properties under applied magnetic fields. Nonetheless, the majority of YBCO nanocomposites with high nanoparticle loads (>20%) suffer from nanoparticle coalescence and degraded superconducting properties. Here, we study the influence of nanoparticle concentration (0-25% mol), size (5 nm-10 nm) and composition (BaHfO , BaZrO ) on the generation of structural defects in the epitaxial YBCO matrix, key parameter for vortex pinning. We demonstrate that flash-heated superconducting nanocomposites with 20 mol% preformed BaHfO or BaZrO perovskite secondary phases feature discrete and small (7 nm) nanoparticles and high density of YBa Cu O (Y248) intergrowths. We identify a synergy between Y248 intergrowth density and small nanoparticles to increase artificial vortex pinning centers. Also, we validate the multideposition process to successfully increase film thickness of epitaxial nanocomposites with competitive critical currents I at 77 K.

Controlling phase transitions in transition metal oxides remains a central feature of both technological and fundamental scientific relevance. A well-known example is the metal-insulator transition which has been shown to be highly controllable while a less well understood aspect of this phenomenon is the length scale over which the phases can be established. To gain further insight into this issue, we have atomically engineered an artificially phase separated system through fabricating epitaxial superlattices consisting of SmNiO\\(_{3}\\) and NdNiO\\(_{3}\\), two materials undergoing a metal-to-insulator transition at different temperatures. By combining advanced experimental techniques and theoretical modeling, we demonstrate that the length scale of the metal-insulator transition is controlled by the balance of the energy cost of the domain wall between a metal and insulator and the bulk energetics. Notably, we show that the length scale of this effect exceeds that of the physical coupling of structural motifs, introducing a new paradigm for interface-engineering properties that are not available in bulk