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Phase transitions in 1-bromoadamantane compared to 1-chloroadamantane: similarities and unique features
Igor V Danilov1, Elena L Gromnitskaya1, Vadim V Brazhkin1
1Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow, 108840, Russia. idanilov@hppi.troitsk.ru.
Ultrasonic studies reveal phase transitions in halogenated adamantanes. The research confirms 1-bromoadamantane
Area of Science:
- Solid-state physics
- Materials science
- Chemical physics
Background:
- Halogenated adamantanes exhibit complex phase transitions.
- Understanding elastic properties is crucial for materials characterization.
Purpose of the Study:
- Investigate elastic properties of 1-chloroadamantane and 1-bromoadamantane.
- Characterize order-disorder and order-quasi-order phase transitions.
- Evaluate the capabilities of the ultrasonic method for studying phase transitions.
Main Methods:
- Ultrasonic method applied to study elastic properties.
- Measurements conducted at temperatures from 77-305 K.
- High pressures up to 1.1 GPa were applied.
Main Results:
- Elastic moduli clearly indicate phase transitions in halogenated adamantanes.
- Detected the lambda-anomaly in elastic properties for the first time.
- Confirmed the M → O phase transition in 1-bromoadamantane as a weak first-order transition with second-order characteristics.
- Determined pressure derivatives of elastic moduli (dB/dP ≈ 8) in the ordered phase at 77 K.
Conclusions:
- Ultrasonic method is highly capable for studying phase transitions.
- The M → O transition in 1-bromoadamantane is a weak first-order transition.
- Lennard-Jones potential can theoretically describe the ordered phase of these compounds.
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