Growth of (NaxKy)FezSe2 crystals by chlorides flux at low temperatures

• (NaxKy)FezSe2 crystals are successfully prepared in NaCl/KCl flux at lower temperatures.
• A reduction reaction that converts K ion in KCl into metal K by Na plays a crucial role in the process.
• The crystals contain more SC phase in volume fraction and exhibit new features in transport.

(NaxKy)FezSe2 crystals are prepared by Na, Fe, and Se as starting materials in NaCl/KCl flux at low temperatures~720 °C. It is found that K is more preferred than Na to enter in between FeSe layers and forms the phase. Thus-obtained crystals contain more superconducting phase in volume fraction and exhibit new features in transport property. Our results provide a promising new synthetic route for preparing quality crystals of iron selenide superconductors.