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An answer combines diffraction under pressure with ac susceptibility volume fractions on the same phase-pure samples.","problem_ref":null,"references":"","settled_by":"Shielding-fraction measurements near 100 percent on phase-pure samples of each polymorph with simultaneous structural determination.","status_note":"Bulk superconductivity was reported in La2PrNi2O7 under pressure (2024) and in pressurized bilayer nickelate crystals up to about $96\\,\\mathrm{K}$ (2025), and superconductivity was also reported in the 1313 polymorph (2025).","title":"Which La3Ni2O7 polymorph carries bulk superconductivity under 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