Phase relations and flux research for zinc oxide crystal growth in the ZnO-Na2O-P2O5 system

The subsolidus phase relations of the ternary system ZnO-Na2O-P2O5 were investigated by means of X-ray diffraction (XRD). There are 7 binary compounds, 4 ternary compounds and 16 three-phase regions in this system. The phase diagrams of the pseudo-binary systems of Na2Zn5(PO4)4-ZnO and NaPO3-ZnO were also investigated by means of XRD and differential thermal analysis (DTA) methods. Na2Zn5(PO4)4-ZnO is an eutectic system with eutectic temperature about 872 °C. Only narrow composition range in the Na2Zn5(PO4)4-ZnO system is suitable as flux to grow ZnO crystals. Two compounds, Na2ZnP2O7 and NaZnPO4, exist in the NaPO3-ZnO system. Two eutectic reactions, Liquid-NaPO3 + Na2ZnP2O7 and Liquid-Na2ZnP2O7 + NaZnPO4, occur existing at about 590 °C and 777 °C, respectively. The NaZnPO4 is formed by the peritectic reaction between liquid and ZnO at about 1007 °C. In the NaPO3-ZnO system, narrow composition range can be used as flux for ZnO crystals growth below 1250 °C.