Avance III spectrometer and a 4.0 mm Bruker HX probe with the exception of Na and fast MAS Ga measured with a 1.6 mm Phoenix HFX probe. MAS and static Al spectra were acquired with a Bloch decay (/2-acq.) pulse sequence and a 1.3 µs excitation pulse corresponding to the /2 pulse optimized on -Al 2 O 3 . For Al, a recycle delay of 6.25 s was used, corresponding to 5T 1 , and 192 scans were summed. Ga MAS and static NMR spectra were recorded with a Hahn-echo (/2- 1 -- 2 -acq.) pulse sequence with a rotorsynchronized (MAS) or 10 µs (static) interpulse delay. Ga spectra were collected with either a Bloch decay pulse sequence or a Hahn-echo pulse sequence with rotor synchronization or, for static Hahn-echo spectra, a 10 µs interpulse delay. For static and 10-¿ 2