Analysis of the thermal and baric evolution of resistance in ${\mathrm{LaBa}}_2{\mathrm{Fe}}_3{\mathrm{O}}_{8+\delta }$ enabled the construction of its pressure-temperature (P-T) phase diagram, which prominently displays a critical boundary, $P_c^{\mathrm{MIT}}\left(T\right)$, marking the transition from localized to hole-type extended states. The relatively low critical pressures $[P_c^{\mathrm{MIT}}\left(T\right)\approx 3–8\text{GPa}]$ suggest that, as $P\to P_c$ in this narrow-gap, strongly correlated charge-transfer system, both the hybridization strength and the charge-transfer character are progressively enhanced, ultimately leading to the emergence of metallicity. Emphasizing the electronic nature of this transition, pressure-dependent structural analyses at room temperature reveal no associated structural phase transition at $P_c^{\mathrm{MIT}}\left(T\right)$; the system retains a (weakly tetragonally distorted) quasicubic perovskite structure with Murnaghan-type compressibility up to 30 GPa. The emergence of hole delocalization and metallic conduction, coupled with suppressed antiferromagnetism, suggests proximity to quantum criticality.

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• Charge order
• Hopping transport
• Localization
• Metal-insulator transition
• Phase diagrams
• Pressure effects
• Antiferromagnets
• Charge-transfer insulators
• Perovskites
• Polycrystalline materials
• Strongly correlated systems
• Magnetization measurements
• Resistivity measurements
• Susceptibility measurements
• X-ray diffraction