COMPRES assemblies with Re-foil or graphite heaters and hBN cylindrical capsules have been used. All assemblies were equipped with B-epoxy windows transparent to X-rays. The pressure and temperature have been either directly measured (thermocouples, pressure standards) or estimated from previously obtained calibration. The characteristic sequence of energy-dispersive X-ray diffraction patterns taken in the course of a melting experiment under pressure is presented in Fig. .