Good quality large ZnGeP 2 (ZGP) crystals have been grown by the horizontal gradient freezing (HGF) technique. Clusters of the disordered cubic ZGP structure assigned as β-ZGP were identified within the ordered tetragonal matrix (α-ZGP). Applying XRD analysis on poly- and single-crystalline samples followed by a whole pattern optimization (Rietveld technique) and a line profile fitting (LPF) analysis enabled the identification of the β-phase. It has been shown that the β-ZGP clusters are coherently oriented with respect to the tetragonal matrix. New result on the thermal expansion of ZGP was obtained, supporting the appearance of order -> disorder transition in ZGP. A reduction in the residual absorption at the near IR could be observed as a result of post growth thermal annealing of ZGP in vacuum, followed by a reduction in the relative amount of the disordered cubic component. The above results suggest that point defects, which are considered to be responsible for the large absorption coefficient in the near IR, also relate to the presence of coherent β-ZGP clusters.