High-Pressure Synthesis of Th3P4-Type c-Zr3N4 Using a Metathesis Reaction and In Situ X-ray Diffraction Studies of the Formation Process

We have successfully prepared highly crystalline Th3P4-type Zr3N4 (c-Zr3N4) using a high-pressure metathesis reaction utilizing a belt-type high-pressure apparatus and determined synthesis conditions. A combination of ZrCl4 and Ca3N2 was used as the Zr and N sources, respectively, which enabled the synthesis of c-Zr3N4 crystals, whereas another combination of Zr and N sources produced only NaCl-type ZrN (delta-ZrN). It was found that 6.5 GPa was the lowest synthesis pressure available for the synthesis of c-Zr3N4 at temperatures ranging from 1400 to 1500 degrees C. In situ X-ray diffraction was performed at 9.3 GPa, which revealed that the appearance of the intermediate phase during heating was key to the synthesis of c-Zr3N4, when the combination of ZrCl4 and Ca3N2 was used as the starting material.