Combined computational and experimental investigation of the La ₂ CuO _{4– x} S _x (0 ≤ x ≤ 4) quaternary system

Significance Discovery of new materials enabling new technologies, from novel electronics to better magnets, has so far relied on serendipity. Computational advances show promise that new materials can be designed in a computer and not in the lab, a proposal called “Materials by Design.” We present here a detailed comparison between theory and experiment, carrying out the synthesis of a high-temperature superconductor in an X-ray beam to elucidate the sequence of chemical reactions as the compound forms. Parallel computations of the stabilities of possible compounds that could form from the selected elements accurately predict the observed reactions. Paired with our chemical intuition, this methodology provides understanding and potentially control of the essential chemical principles responsible for stabilizing virtually any compound.