Sngle crystals of Tb0.3Dy0.7Fe2 have been obtained by CZ technique with cold crucible. The formation mechanism of defects such as RFe3 strips, Widmanstatten precipitates (WSP), twins and inclusions were investigated in detail. They are generated by different phase relations and conditions of solidification. The geometrical morphology depends on the crystallographic orientation or the position of the interface. The relationship between growth conditions and compositions of starting materials has been discussed based on the normal freezing theory for rare earth-rich growth environment. Various growth rates were selected for growing defect-free single crystals of Tb0.3Dy0.7Fe2. Optimized conditions are a growth rate of 10-30mm/h, temperature gradient of 110-140degreesC/cm and starting composition of Tb0.3Dy0.7Fey (y = 1.78-1.85). (C) 2002 Published by Elsevier Science B.V.