The bound state of two dislocations known as a penta-hepta defect (PHD) is a generic object in hexagonal patterns. Its motion provides an important mechanism of wavevector(s) selection. In this paper the structure and dynamics of penta-hepta defects in hexagonal patterns is studied in the framework of envelope equations. Analytical solution for phase field of moving PHD is found in the far field, which generalizes the static solution due to Pismen and Nepomnyashchy (1993). The mobility tensor of PHD is calculated using combined analytical and numerical approach. The results for the velocity of PHD climbing in slightly non-optimal hexagonal patterns are in good agreement with numerical simulations of amplitude equations. Interaction of penta-hepta defects in optimal hexagonal patterns is studied numerically.
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