Spontaneous ordering in ultra-large anion size-mismatched BaZr (S_1−xO_x)₃

Chalcogenide perovskite semiconductors, with their excellent optical absorption, chemical stability, and lack of toxicity, have emerged as a promising alternative to traditional halide perovskites. Through first-principles density functional theory, we show that despite the large lattice mismatch between the prototypical BaZr S 3 and BaZr O 3 chalcogenide perovskites, BaZr ( S 1 − x O x ) 3 can form low-energy ordered lattices that significantly reduce strain. The bandgap dependence of the resulting ordered compound on x is found to exhibit double Vegard's law behavior, having two distinct linear regions, associated with an underlying distorted or undistorted perovskite structures.