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Updated: Jan 11, 2026
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Tetragonal BaCoO 3 : A Co 4+ Ferromagnetic Mott Insulator
Mingyu Xu1, Haozhe Wang1, Krishna Prasad Koirala2
1Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States.
None:
We report the stabilization of the metastable body-centered tetragonal (BCT) phase of BaCoO3 (BCT-BaCoO3) under high-pressure (15 GPa) and high-temperature (1200 °C) conditions using a mixture precursor. This double perovskite adopts the EuTiO3-type structure (space group I4/mcm), as confirmed by powder X-ray diffraction and high-resolution STEM. X-ray photoelectron spectroscopy indicates a predominant Co4+ oxidation state without detectable oxygen vacancies. Magnetization and heat capacity measurements reveal ferromagnetic ordering at T C ∼ 107 K, attributable to the BCT-BaCoO3 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-BaCoO3 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.
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