The synergistic interaction of different components in heteronanocrystals induces interfacial phenomena and novel functionalities. Nonetheless, effective technologies to design and fabricate heteronanocrystals with materials on demand are still missing. Rich heterostructures in a copper patina are known to form at room temperature and under atmospheric pressure. The redox process of copper tarnish inspired the discovery of a simple strategy to achieve heteronanocrystals that contained elements from group 3–11 and group 14–16. The interface redox-induced method is self-regulating at ambient conditions and applicable for metal, semiconductor, and dielectric materials. The enhanced interface bonding endows the heteronanocrystals with outstanding stability and catalytic performance, while the modular approach enables the design and fabrication of heteronanocrystals with intended materials to meet different purposes.

Ferroelectric thin/thick films with large electrocaloric (EC) effect are critical for solid state cooling technologies. Here, large positive EC effects with two EC peaks in a broad temperature range (~100 K) were obtained in 0.95Pb_0.92La_0.08(Zr_0.70Ti_0.30)_0.98O₃-0.05BiFeO₃ (BFOLa-codoped PZT) epitaxial thin films deposited on the (100), (110) and (111) oriented SrTiO₃ (STO) substrates by a sol-gel method. The thin film deposited on the (111) oriented STO substrate exhibited a stronger EC effect (~20.6 K at 1956 kV/cm) near room temperature. However, the thin films deposited on the (100) and (110) oriented STO substrates exhibited a stronger EC effect (~18.8 K at 1852 kV/cm and ~20.8 K at 1230 kV/cm, respectively) around the peak of the dielectric permittivity (T_m, ~375 K). Particularly, as the direction of the applied electric field was switched (E < 0), the ΔT of the (100)-oriented thin films around T_m was enhanced significantly from 18.8 K to 38.1 K. The self-induced-poling during the preparing process maybe plays a key role on the magic phenomenon. It can be concluded that the BFOLa-codoped PZT epitaxial thin films are promising candidates for application in the next solid-state cooling devices.