Pressure Induced Unstable Electronic States upon Correlated Nickelates Metastable Perovskites as Batch Synthesized via Heterogeneous Nucleation

Establishing condensed matters at their thermodynamically metastable or unstable structures demonstrates merit in the adjustability of their electronic structures, benefiting the discovery of emerging new material functionalities and applications. Herein, a molten-salt assisted heterogeneous nucleation approach is demonstrated to significantly improve the effectiveness in batch synthesis of metastable perovskites correlated oxides, such as rare-earth nickelates (ReNiO₃) with various rare-earth compositions. In contrast to their conventional synthesis via solid state reactions, herein the metastable ReNiO₃ is heterogeneously precipitated together with potassium chloride (KCl) within the liquid phase of KCl molten-salt that effectively dissolves the Ni-/Re- precursors and largely enhances their reaction homogeneity. With this solid base overcoming their synthesis metastabilities, the beyond conventional electronic transportation of ReNiO₃ under high pressure is explored. It breaks the conventional thermodynamic equilibrium and triggers the formation of new electronic structures associated with unstable insulating and metallic SmNiO₃ beyond already known manners. The unstable insulating SmNiO₃ exhibits nontemperature-dependent transportation character similar to saturation or bad metals but preserves 2–3 orders higher electronic conductivity, while a kinetic related hysteresis is observed in the temperature-dependent transportations of the unstable metallic SmNiO₃. These discoveries with nonequilibrium correlated materials are worthy to be explored further.