Figure 5
From: Using pressure to unravel the structure–dynamic-disorder relationship in metal halide perovskites
The frequency of the N–H symmetric stretching vibration [\(\nu _s\)(NH\(_3^+\))] of the methylammonia (a) as a function of temperature at ambient pressure and (b) as a function of pressure at room temperature. The pressures at which the phase transitions occur are marked with vertical dashed lines and the different phases are indicated. The inset shows a representative Raman spectrum in the range of the N–H stretching vibrations around 3000 cm\(^{-1}\).
