From Polycrystalline Synthesis to Single‐Crystal Growth: Achieving High‐Optical‐Quality BaGa ₂ GeSe ₆ crystal via a Dual‐Zone Approach

ABSTRACT BaGa 2 GeSe 6 crystal is a promising material for mid‐ to far‐infrared frequency conversion. The synthesis of phase‐pure polycrystalline BaGa 2 GeSe 6 is crucial for growing high‐quality single crystals. In this paper, the transportation and reaction properties of the dual‐zone synthesis of BaGa 2 GeSe 6 polycrystalline materials were investigated. The quenching technique was employed to identify major reaction intermediates, which PXRD analysis revealed to be α ‐BaGa 2 Se 4 . The dual‐zone synthesis is used to eliminate GeSe 2 escape, and selenium vapor transported from the low‐temperature zone reacts with Ba, Ga, and Ge in the high‐temperature zone (1203 K) to form pure BaGa 2 GeSe 6 , as confirmed by XRD. Using this phase‐pure polycrystalline material with extra GeSe 2 , a large single crystal of BaGa 2 GeSe 6 with the dimensions of 24 mm in diameter and 60 mm in length was successfully grown by the vertical Bridgman method. A sample sized 6 × 6 × 10 mm 3 was fabricated from the as‐grown crystal. The as‐grown BGGSe crystal exhibited a narrow FWHM of 39.60'' and broad optical transmittance.