Decay mechanism of optical phonons in γ-CuI

Temperature-dependent frequencies and linewidths of transverse-optical (TO) and longitudinal-optical (LO) in γ–CuI were fitted according to the anharmonic phonon coupling theory. The results indicate that the asymmetric three-phonon and symmetric four-phonon processes are both responsible for the decay of LO and TO phonons in γ–CuI. Additionally, the possible decay channels are also suggested as: TO (135 cm-1) →LA (∼100 cm-1) +TA (35 cm-1) at L point and three TA (45cm-1) at X point; LO (152 cm-1) → LA (∼102 cm-1) +TA (∼50 cm-1) or three TA (50cm-1) at K point in Brillouin zone. These results are meaningful for the future applications of γ–CuI in optoelectronic and electronic fields.