First Synthesis of Millimeter-Sized Single Crystals of High-Entropy Perovskite (La_0.25Pr_0.25Sm_0.25Gd_0.25)_1-xCa_xMnO₃ Oxides

We report the first successful synthesis of millimeter-sized single crystals of high-entropy perovskite manganites with the composition (La_0.25Pr_0.25Sm_0.25Gd_0.25)_1-xCa_xMnO₃ (x = 0.3, 0.4, 0.5). Single crystals exceeding 2 mm in size were grown via a flux method using a PbF₂/PbO/B₂O₃ system. The X-ray diffraction patterns exhibit only (0k0) series reflections, indicating strong preferred orientation and high-quality single-crystal character. Scanning electron microscopy reveals dense, grain-boundary-free surfaces. Energy-dispersive X-ray spectroscopy elemental mapping shows uniform distribution of all constituent elements without detectable segregation or secondary phases, confirming the formation of a true high-entropy solid solution in single-crystal form. To the best of our knowledge, based on the publicly searchable literature, this is the first report of bulk single-crystalline high-entropy perovskite oxide. This breakthrough provides a much-needed single crystal experimental platform for systematically investigating the intrinsic magnetotransport mechanisms of compositionally complex strongly correlated oxides, free from grain-boundary interference.