Abstract
We report the stabilization of the metastable body-centered tetragonal (BCT) phase of BaCoO(3) (BCT-BaCoO(3)) under high-pressure (15 GPa) and high-temperature (1200 °C) conditions using a mixture precursor. This double perovskite adopts the EuTiO(3)-type structure (space group I4/mcm), as confirmed by powder X-ray diffraction and high-resolution STEM. X-ray photoelectron spectroscopy indicates a predominant Co(4+) oxidation state without detectable oxygen vacancies. Magnetization and heat capacity measurements reveal ferromagnetic ordering at T (C) ∼ 107 K, attributable to the BCT-BaCoO(3) phase. Above this temperature, the mixed-phase sample exhibits Curie-Weiss paramagnetism, a low-spin to high-spin crossover upon cooling, and a possible intermediate-spin state at elevated temperatures. Resistivity data indicates insulating behavior with weak magnetoresistance. DFT and DFT + DMFT calculations suggest that the insulating state originates from an orbitally selective transition sensitive to the nominal valence of the Co-d shell. The metastable BCT-BaCoO(3) phase cannot be retained in pure form at ambient pressure but can be stabilized by embedding it in a disordered mixture, offering a potential route to discover and preserve other high-pressure phases under ambient conditions.