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The Fe²⁺‐Mg distribution coefficients (K_D) between perovskite/postperovskite and ferropericlase were determined in a (Mg_0.9Fe_0.1)₂SiO₄ bulk composition. High‐pressure and high‐temperature experiments were carried out between 36 and 128 GPa and 1760–2170 K in a laser‐heated diamond anvil cell (LHDAC). Chemical analyses were made on recovered samples with transmission electron microscope (TEM) and field‐emission‐type scanning electron microscope (FE‐SEM). All the samples exhibited a strong heterogeneity in iron content caused by relatively large temperature gradient during laser‐heating, being depleted at the center of the hot spot and enriched at the margin. The K_D values measured from coexisting perovskite/postperovskite and ferropericlase showed apparently very large variation in each sample, which could be the source of considerable discrepancy among previous measurements of …