Photoacoustic detection of phase transitions at low temperatures in CsPbCl₃ crystals

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Phase transitions in CsPbCl₃ crystals have been explored by photoacoustic (PA) method in a wide temperature range of 150--300 K. The PA signals, induced by ns-pulsed laser excitation of electronic states and detected with a piezoelectric transducer, are thermoelastic ultrasonic waves lasting for hundreds of microseconds. The wavelet analysis of the PA wave has clarified that the thermoelastic wave includes several MHz components. The PA signals have been made use of in order to examine phase transitions at low temperatures in the crystal. Changes of PA signals indicate that two phase transitions take place at low temperatures around 200 K. The types of phase transitions are discussed taking into recent experimatal results.