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Over the decades, the application of mechanical force to influence chemical reactions has been called by various names: mechanochemistry, tribochemistry, mechanical alloying, to name but a few. The evolution of these terms has largely mirrored the understanding of the field. But what is meant by these terms, why have they evolved, and does it really matter how a process is called? Which parameters should be defined to describe unambiguously the experimental conditions such that others can reproduce the results, or to allow a meaningful comparison between processes explored under different conditions? Can the information on the process be encoded in a clear, concise, and self-explanatory way? We address these questions in this Opinion contribution, which we hope will spark timely and constructive discussion across the international mechanochemical community.

The electrochemical and chemical oxidation of the defect perovskite SrFeO 2.5 to the cubic perovskite SrFeO 3 at ambient temperature in alkaline electrolyte are shown to be in principle reversible processes with the appearance of intermediate compounds; the oxidation can be described by the formation of line phases SrFeO 2.75 and SrFeO 2.87 and one solid solution range SrFeO 3-x with 0 e x e 0.03. The structure of the brownmillerite type parent phase is characterized by the presence of stacking faults in the octahedral and tetrahedral sequence of layers whose concentration increases significantly upon formation of the intermediate phases. Models based on observed microscopic features are discussed in order to explain the unusual phenomenon of room temperature oxygen transport.

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We describe an experiment in a special device, which permits to quantify the energy input into a solid sample and to follow the products of mechanochemical synthesis step by step. The application of the device is tested on the ''glycine-oxalic acid dihydrate'' system, in which two products are formed concomitantly on co-grinding.Mechanochemical synthesis has been known for at least a century, 1 but the interest in it has grown enormously during the last decade, 2 in particular, in relation to obtaining new organic compounds, salts, and co-crystals. 3 Many examples of successful synthesis achieved on co-grinding a powder mixture in a mortar or in a mill have been described. However, the mechanisms of these transformations remain far from being understood, although several approaches and models have been proposed. The latter are based on considering eutectic melting, 4 dissolution in a small amount of liquid added on cogrinding or present in the reagents as a crystal solvent, 5 a gas-solid reaction resulting from the sublimation of one or more components, 6 and direct solid-state interdiffusion of the components. 2,7 One of the major problems which is intrinsic to the mechanochemical reactions is that a sample is treated not continuously, but in mechanical pulses. As a result, the total time of the mechanical treatment in a mill, or in another mechanical device, differs from the actual time, during which the sample was subjected to mechanical pulses. 2,4b,5a,8 The energy of pulses, their duration, the shape of a pulse, and the time between the pulses are the parameters, which are very important for the reaction outcome. However, it is practically impossible to control them, when either a manual grinding or the treatment in a commonly used mechanical device (a mill, an attritor, an automatic mortar, etc.) is considered. 2,4b,5a,8 In the present communication we describe a model experiment accomplished in a special device designed and manufactured for the detailed studies of mechanochemical reactions in one-or multi-component systems, which enable to treat a sample by individual mechanical pulses of variable and controllable energy, duration, and frequency. 9 This device has been tested on a model system ''glycine-oxalic acid dihydrate'' 10 and allowed us to follow the products of co-grinding formed at the different steps of the transformation.