²⁹Si MASNMR spin-lattice relaxation study of α-, β-, and amorphous silicon nitride

The spin-lattice relaxation times, T₁, in α-, β-, and amorphous Si₃N₄ have been obtained for the first time, using a multiple-pulse saturation recovery method. The saturation recovery of the ²⁹Si magnetization follows exponential behavior under magic-angle spinning conditions, within the limits of experimental error. A rather wide dispersion of T₁ values is observed for the phases of Si₃N₄: 284±29 min (-46.686 ppm) and 260±23 min (-48.812 ppm) for the α-phase, 36±4 min for the β-phase, and 11±1 min for the amorphous phase, assuming an exponential recovery. The values obtained for the exponent in the power-law fitting are 0.599(9) (-46.686 ppm) and 0.61(1) (-48.812 ppm) for the α-phase, 0.52(2) for the β-phase, and 0.53(3) for the amorphous phase.