Disordering in pyridine at high pressures

Pyridine has recently attracted significant attention because of its polymorphism and capability to form polymerized hydrocarbons at high pressures that have great technological potential. In this work, liquid and solid phases of pyridine have been studied by dielectric spectroscopy and the pulsed ultrasonic method at pressures $P < 4.2$ GPa in the temperature range $78$ K $< T < 350$ K. These studies allow determining more accurately the boundary between low- and high-pressure phases. It has been shown that crystallization from a melt to a low-pressure phase is accompanied not only by the formation of a crystalline phase but also by the transition of one-fifth of the sample to a glassy state. Before the melting of the low-pressure phase, a transition occurs to a disordered state having a high dielectric constant and a high absorption coefficient of ultrasound. The high-pressure phase does not have all these features.