SEM and optical observations and single-crystal diffraction measurements for WP, showing SEM images of WP prepared at 5 GPa and different temperatures with different holding durations at (a) 5 GPa and 1600 °C for 30 min, (b) 5 GPa and 1600 °C for 60 min and followed by quenching, (c) 5.0 GPa and 1600 °C for 60 min with a cooling rate of 40 °C/min, (d) 5.0 GPa and 2400 °C for 5 min, (e) 5.0 GPa and 3000 °C for 0.5 min with a cooling rate of 600 °C/min, (f) 5.0 GPa and 3200 °C for 0.5 min with a cooling rate of 800 °C/min, (g) optical image of WP synthesized at 3200 °C. Size of the background grid is 1 mm × 1 mm, (h) Laue diffraction pattern, and secondary symmetry of the (100) plane is identified, (i) single-crystal diffraction patterns. In panels (h) and (i), diffraction data are taken at room temperature.