A contribution to the understanding of the polyamorphism situation in triphenyl phosphite

Abstract

Triphenyl phosphite (TPP) is now well known to exhibit an intriguing transformation of the supercooled liquid. The transformation was firstly interpreted as a first-order polyamorphic transition between the supercooled liquid and an apparently amorphous state different from the glass and the ordinary liquid, the so-called glacial state. In this paper, we describe and analyze, from experimental investigations (Raman spectroscopy, calorimetric measurements, X-ray and neutron diffraction), the transformation into the glacial state and the structural organization of this state. The latter is interpreted as a heavily nucleated state composed of nanocrystals of the stable crystalline phase embedded in the matrix of non-transformed supercooled liquid. The origin of the intriguing relative stability of this state could result in the combination of two phenomena: the time lag required to attain steady-state values of the nucleation rate (connected to the high viscosity of TPP), and a high nucleation rate in the temperature range where the growth rate is low. These results converge into a description of the glacial state as a mixed supercooled liquid/crystallites state, and then contradict recent claims that the glacial state of TPP is a homogeneous amorphous phase.