Nonstoichiometry of ZnGeP2 crystals probed by static tensimetric method

The nonstoichiometry of ZnGeP2 has been determined based on the p–T dependences measured above ZnP2–Ge samples in the temperature range of 980–1225 K by a high-sensitive and precise tensimetric static method with a quartz Bourdon gauge. Scanning of the compositional range 49–51 mol% ZnP2 in the closed system and construction of the p–T dependences were possible due to incongruent evaporation of ZnGeP2 and formation of volatile species Zn(g), P4(g) and P2(g). The maximum homogeneity range of the solid ZnGeP2 was determined between 50.03 and 49.61 mol% ZnP2 at a temperature of 1128 K, based on the inflection points on the p–T dependences, corresponding to transitions of the three-phase (solid–solid–vapor) equilibrium to a two-phase (solid–vapor) one and vice visa. The nonstoichiometry as the overall concentration of defects is considered to gain a better insight into the defect chemistry of ZnGeP2.