Structural defects were studied in the nonlinear optical material ZnGeP2 (ZGP) grown by the vertical Bridgman technique from the melt. Progress in ZGP growth with sufficiently perfect structure allowed us observe the Borrmann effect and to apply X-ray transmission topography method based on this effect for the first time for ZGR Types of defects were defined by comparison of the experimental and simulated topographs. In as-grown ZGP crystals the topography found growth striation, various dislocations, coherent and semi-coherent particles of second phases, inclusions, in the initial part of the crystal with compositions lying along ZGP-GeP2 pseudobinary cut. Inclusions forming solute trails in the end part of ZGP ingots with compositions lying along the ZGP-ZnP2 pseudobinary cut. The dislocation density changed from N-d similar to 3.5 x 10(3) cm(-2) to similar to 2.5 x 10(2) cm(-2) from the onset to the end of the ingot, respectively. FWHM of rocking curves for as-grown ZGP ranger from 13 '' to 35 ''. A high optical absorption coefficient in the 0.65-2.5 mu m spectral region, always existing in as-grown ZGP, can be reduced by thermal annealing and electron irradiation down to similar to 0.02 cm(-1) at 2.06 mu m. (C) 2014 Elsevier B.V. All rights reserved.