Microstructural analysis of hydrogen absorption in 2NaH + MgB2

Transmission electron microscopy and in situ X-ray diffraction have been used to characterize the hydrogenation mechanism of ball-milled 2NaH + MgB2. Hydrogen absorption was performed under 50 bar hydrogen while heating from room temperature to 400 °C. A new and unknown hydride phase is observed at about 280 °C. This phase remains stable up to 320 °C and subsequently disappears, followed by the formation of perovskite-type NaMgH3 at about 330 °C. At 380 °C, crystals of NaBH4 appear and grow.