Rapid shifts in the energy, technological, and environmental demands of materials science call for focused and efficient expansion of the library of functional inorganic compounds. To achieve the requisite efficiency, we need a materials discovery and optimization paradigm that can rapidly reveal all possible compounds for a given reaction and composition space. Here we provide such a paradigm via in situ X-ray diffraction measurements spanning solid, liquid flux, and recrystallization processes. We identify four new ternary sulfides from reactive salt fluxes in a matter of hours, simultaneously revealing routes for ex situ synthesis and crystal growth. Changing the flux chemistry, here accomplished by increasing sulfur content, permits comparison of the allowable crystalline building blocks in each reaction space. The speed and structural information inherent to this method of in situ synthesis provide an experimental complement to computational efforts to predict new compounds and uncover routes to targeted materials by design.D iscovering new materials is a crucial step to address largescale problems of energy conversion, storage, and transmission and other technological needs whether seeking bulk phases or thin films. Dense inorganic materials are desired for their tunable transport, magnetism, optical absorption, and stability, but their existence in general cannot be predicted with the near certainty of that of metastable organic and organometallic compounds. Whereas the desire to efficiently locate and assemble inorganic materials is great, it is hindered by traditional solid-state synthetic methods-at high temperatures often only the energy-minimum thermodynamic product is obtained. To strive toward an arena where metastable compounds can be discovered rapidly and made systematically, here we conduct reactions within liquid fluxes and use in situ monitoring to capture signatures of new phases, even when they quickly dissolve in the melt.Convective liquid fluxes (salts, metals, or oxides) can serve as reaction media that aid diffusion and enable rapid formation of compounds at temperatures far below their melting points (1-6). The flux can be nonreactive or reactive; in the latter case the flux itself becomes incorporated into the product (7,8). This wellestablished approach has demonstrated the prolific discovery of novel inorganic materials grown out of low-melting fluxes, from oxides and other chalcogenides (9-12), to pnictides (13,14), to intermetallics (15), many of which cannot be attained by direct combinations of the elements. Despite the variety of metastable phases formed in these reactions, the classical approach is to predetermine a given set of reaction conditions (e.g., time, temperature, and heating and cooling rates) and wait for completion to isolate and identify the formed compounds. It is not possible to observe how the reaction system itself has arrived at the isolated compound, whether the crystalline material formed on heating, on cooling, or on soaking at the given high temperature,...

At first sight, the quenched tetragonal spinel CuMn(2)O(4) can be formulated with Cu(2+) and Mn(3+), implying that the tetrahedral site is Jahn-Teller (JT)-active Cu(2+) and the octahedral site is JT-active Mn(3+). High-resolution, high-momentum-transfer neutron scattering analysis suggests that the sample has approximately 30% inversion: Mn on the tetrahedral Cu site with compensating Cu on the octahedral site. Reverse Monte Carlo (RMC) analysis of the pair distribution function allows details of metal-oxygen connectivity to be probed in a manner that is significantly on the local rather than the average scale. Bond valence analysis of the RMC supercell reveals that both JT ions disproportionate to higher and lower valence states as a means of avoiding their JT tendency, particularly on the tetrahedral site. The occurrence of Cu(3+) in particular is suggested for the first time and is supported by X-ray photoelectron spectroscopy data. The bimodal distribution of O-Cu-O bond angles at the tetrahedral site (distinct from what is seen for O-Mn-O bond angles) further reveals a hidden distinction between sites previously considered to be equivalent. Application of total scattering techniques originally developed for highly disordered materials permits the examination of nanoscale crystalline structure with elemental specificity that is not available in traditional reciprocal-space analysis.

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