Vibrational properties of CuInP2S6 across the ferroelectric transition

Robust Threshold-Switching Behavior Assisted by Cu Migration in a Ferroionic CuInP2S6 Heterostructure

“…Figure a presents an optical image of the Cu/CIPS/Gr device, while Figure b displays the representative Raman spectra of CIPS at different positions (active area 1 and nonactive area 2) and different states (pristine state and cycled state). According to previous reports, − the Raman peaks at 70 and 315 cm –1 represent the cation vibration and the peak at 264 cm –1 represents the S–P–S vibration in CIPS, as labeled in Figure b. We noticed a clear difference in the Raman spectra between the active area 1 (on top of the Cu electrode) and the nonactive area 2 (without contact with the Cu electrode) even in the pristine state.…”

Investigating Strain between Phase-Segregated Domains in Cu-Deficient CuInP2S6

“…Our calculated Raman spectra are also in agreement with previous calculations for CIPS. 24 Interestingly, the single peak at 311.9 cm −1 determined by Neal et al 24 is split into two subpeaks at 316.1 and 294.5 cm −1 in our results, which are consistent with our measurements. Our predicted Raman frequency shifts for the peak pairs in pure-phase CIPS and IPS (i.e., peaks with similar mode vibrations) agree with our measurements.…”

“…However, trends can nevertheless be elucidated (see the overall agreement of the calculated Raman spectra in Figure d with the experimental data in Figure c, as well as Table S1). Our calculated Raman spectra are also in agreement with previous calculations for CIPS . Interestingly, the single peak at 311.9 cm –1 determined by Neal et al is split into two subpeaks at 316.1 and 294.5 cm –1 in our results, which are consistent with our measurements.…”

“…While the exact number of peaks between the two pure-phase materials differs greatly, in general it can be seen that the Raman spectra exhibit some peaks that are common to all metal thiophosphate materials. ,,− The general groupings of Raman peaks are as follows: peaks below 100 cm –1 correspond to extended vibrational modes involving the metal cations, and peaks between 100–350 cm –1 correspond to deformations of the octahedral cages and involve the S and P atoms. The sharp peak around 380 cm –1 is dominated by out-of-plane P–P and S valence vibrations, and the high-frequency modes between 540–620 cm –1 correspond mainly to P–P valence vibrations.…”

“…The Kohn–Sham equations were solved using a plane wave basis set with an energy cutoff of 500 eV. The initial ferroelectric structure of CIPS was from the measured ferroelectric bulk structure and was optimized using the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional, including the D3 correction of Grimme, as the inclusion of London dispersion was shown to be important. , An 8 × 8 × 3 k -point sampling was used in this case. The initial paraelectric IPS bulk structure was taken from the crystal structure of ref , optimized using PBE+D3 and 8 × 4 × 3 k -point sampling.…”