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We demonstrate the application of a simple equilibrium model based on elasticity theory to estimate the geometric limits of dislocation-free core/shell nanowires (NWs). According to these calculations, in a coherent core/shell structure, tangential strain is the dominant component in the shell region and it decreases quickly away from the heterointerface, while axial strain is the dominant component in the core and is independent of the radial position. These strain distributions energetically favour the initial relief of axial strain in agreement with the experimental appearance of only edge dislocations with line directions perpendicular to the NW growth axis at the core/shell interfaces. Such dislocations were observed for wurtzite InAs/InP and zincblende GaAs/GaP core/shell NWs with dimensions above the coherency limits predicted by the model. Good agreement of the model was also found for experimental results …