Tetragonal BaCoO 3 : A Co 4+ Ferromagnetic Mott Insulator

Xu, Mingyu [Michigan State University, East Lansing, MI (United States)]; Wang, Haozhe [Michigan State University, East Lansing, MI (United States)] (ORCID:000000034820833X); Koirala, Krishna Prasad [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)]; Melnick, Corey [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Peng, Cheng [Michigan State University, East Lansing, MI (United States)] (ORCID:0000000289772749); González-Rivas, Mario U. [University of British Columbia, Vancouver, BC (United States)] (ORCID:0000000336674149); Lu, Jiaqi [University of Michigan, Ann Arbor, MI (United States)]; Wang, Le [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000277309482); Freese, Jessica [University of British Columbia, Vancouver, BC (United States); University of Saskatchewan, Saskatoon, SK (Canada)]; Engelhard, Mark H. [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000255430812); Du, Yingge [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000196801950); Ke, Xianglin [Michigan State University, East Lansing, MI (United States)]; Green, Robert J. [University of British Columbia, Vancouver, BC (United States); University of Saskatchewan, Saskatoon, SK (Canada)]; Hallas, Alannah M. [University of British Columbia, Vancouver, BC (United States)] (ORCID:0000000208920982); Li, Jie [University of Michigan, Ann Arbor, MI (United States)]; Kotliar, Gabriel [Brookhaven National Laboratory (BNL), Upton, NY (United States); Rutgers University-New Brunswick, Piscataway, NJ (United States)]; Xie, Weiwei [Michigan State University, East Lansing, MI (United States)] (ORCID:0000000255008195)

doi:10.1021/acs.jpcc.5c03983

DOE OSTI · 3001318

Tetragonal BaCoO 3 : A Co 4+ Ferromagnetic Mott Insulator

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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 hightemperature (1200 °C) conditions using a mixture precursor. This double perovskite adopts the EuTiO 3 -type structure (space group I4/mcm), as confirmed by powder Xray 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.

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Xu, Mingyu [Michigan State University, East Lansing, MI (United States)], Wang, Haozhe [Michigan State University, East Lansing, MI (United States)] (ORCID:000000034820833X), Koirala, Krishna Prasad [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)], Melnick, Corey [Brookhaven National Laboratory (BNL), Upton, NY (United States)], Peng, Cheng [Michigan State University, East Lansing, MI (United States)] (ORCID:0000000289772749), González-Rivas, Mario U. [University of British Columbia, Vancouver, BC (United States)] (ORCID:0000000336674149), Lu, Jiaqi [University of Michigan, Ann Arbor, MI (United States)], Wang, Le [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000277309482), Freese, Jessica [University of British Columbia, Vancouver, BC (United States); University of Saskatchewan, Saskatoon, SK (Canada)], Engelhard, Mark H. [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000255430812), Du, Yingge [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000196801950), Ke, Xianglin [Michigan State University, East Lansing, MI (United States)], Green, Robert J. [University of British Columbia, Vancouver, BC (United States); University of Saskatchewan, Saskatoon, SK (Canada)], Hallas, Alannah M. [University of British Columbia, Vancouver, BC (United States)] (ORCID:0000000208920982), Li, Jie [University of Michigan, Ann Arbor, MI (United States)], Kotliar, Gabriel [Brookhaven National Laboratory (BNL), Upton, NY (United States); Rutgers University-New Brunswick, Piscataway, NJ (United States)], Xie, Weiwei [Michigan State University, East Lansing, MI (United States)] (ORCID:0000000255008195). 2025-10-22. Tetragonal BaCoO 3 : A Co 4+ Ferromagnetic Mott Insulator. https://doi.org/10.1021/acs.jpcc.5c03983

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