2018/09/03 by Luigi Giacomazzi, Giacomazzi, Luigi
Materials Science · Engineering · #Advanced ceramic materials synthesis #Acoustic Wave Resonator Technologies #Ferroelectric and Piezoelectric Materials
paper · pdf · doi:10.48550/arxiv.1809.00610
We present a first-principles investigation of the localization properties of vibrational modes in amorphous silicon nitride (a-Si3N4). Our investigation further confirms that the vibrational modes underlying the peak at ∼471 cm-1 in the infrared spectrum of silicon nitride mainly consist of nitrogen motion in the direction normal to the plane defined by the three Si nearest neighbors. In-plane stretching of N--Si bonds becomes largely dominant above ∼700 cm-1. In particular vibrational modes underlying the infrared peak at 825 cm-1 arise from the N--Si bond stretching motions. If N--N homopolar bonds were present, we show that N--N bond stretching occurs above ∼1100 cm-1. Furthermore, we investigate the localization properties of vibrational modes by calculating their inverse participation ratio (IPR) and phase quotient. From this analysis we infer that modes above 600 cm-1 shows a progressive increase of the localization degree and optic-like behavior, especially above 1000 cm-1. At about 650 cm-1, given the considerable IPR value, and on the basis of projectional analysis on silicon-breathing-like motions of the NSi3 units, we suggest that vibrational modes may involve correlated motions of neighboring SiN4 tetrahedra.