Single Crystal Growth and Magnetic Properties of BaCuO ₂

High-quality BaCuO 2 single crystals were successfully grown by a high-temperature BaCl 2 ·2H 2 O flux method under an optimal slow-cooling condition of 1 °C/h within the temperature window of 980–800 °C. Structural characterizations confirm that BaCuO 2 crystallizes in the cubic Im - 3m structure with excellent crystallinity, homogeneous elemental distribution, and negligible oxygen-vacancy concentration. Magnetic susceptibility, magnetization, and specific-heat measurements consistently reveal an antiferromagnetic transition near T N = 11 K accompanied by pronounced short-range magnetic correlations. Although the Curie–Weiss fitting yields a positive Weiss temperature, the low-temperature thermodynamic response establishes an antiferromagnetic ground state arising from competing magnetic exchange interactions within the Cu–O cluster network. Importantly, the present single-crystal study demonstrates that BaCuO 2 is intrinsically an insulating oxide rather than a semiconducting or superconductivity-related material, highlighting the crucial importance of high-quality single crystals for distinguishing intrinsic physical properties from impurity-driven effects in complex cuprate systems.