Size dependence of the Raman spectra in an amorphous–nanocrystalline mixed phase: the glacial state of triphenyl phosphite

Abstract

Raman scattering investigations on triphenyl phosphite, performed in both the low-and high-wavenumber ranges, provide a detailed description of the glacial state. The latter can be described as a two-phase (amorphous-nanocrystalline) system if it is prepared by isothermal aging in the 210-222 K temperature range. From two different procedures the nanocrystalline volume fraction can be determined in glacial states prepared in the above temperature range. The Raman spectra in the range 840-1640 cm −1 reveals that T a = 224 K is a critical temperature from which the supercooled liquid isothermally transforms into a microstructure rather than nanocrystallized domains. In this case the volume of the non-transformed supercooled liquid remaining in the intergranular space was estimated with respect to the volume of crystallized matter.

Micro-structural investigations in the glacial state of triphenyl phosphite

“…However the Raman susceptibility of the glacial state, plotted in Fig. 2, differs from that of the other amorphous states on the whole frequency range, as previously observed [15,17,18,23]. Fig.…”

“…This relationship between spectra of the glacial and crystalline states suggest that Raman bands in the glacial state results from an homogeneous broadening of the phonon peaks connected to a size effect. By comparison to the spectrum of the crystal the spectral changes observed during the glaciation are considered as crystalline signatures [15,17,18,23] characteristic of sub-micro crystallites of the stable phase, especially the 150 cm À1 band only observed in the crystal.…”

“…The discovery of an apparently amorphous state (glacial state) by Ha et al [4,5] at ambient pressure and in a very accessible temperature range (above 200 K) has given the opportunity to analyze a supposed example of polyamorphic transformation by usual laboratory equipments. However different descriptions of the glacial state emerge from extensive investigations: a defect-ordered phase [4][5][6][7][8] inherent to the development of a locally preferred structure which is not space-tiling [8][9][10], plastic or liquid crystal [11], strong liquid [12], highly correlated liquid [13], a second glassy state corresponding to a second liquid [14], and liquid/crystallites mixed system [15][16][17][18][19][20][21][22][23].…”

“…Structural investigations in the glacial state of triphenyl phosphite by the use of techniques which probe the longrange order [15,16,18,23,24] have led to a description of the glacial state as composed of crystallites of the stable phase coexisting with the non-transformed supercooled liquid. The crystallite size and the volume fraction crystallized were determined drastically dependent on the temperature at which the glacial state is isothermally formed [16,18,19], independently on the thermal path followed to reach the temperature (T a ) of the isothermal transformation [23] (direct quench from room temperature down T a , or quench below T g and rapid heating up to T a ).…”

“…The crystallite size and the volume fraction crystallized were determined drastically dependent on the temperature at which the glacial state is isothermally formed [16,18,19], independently on the thermal path followed to reach the temperature (T a ) of the isothermal transformation [23] (direct quench from room temperature down T a , or quench below T g and rapid heating up to T a ). The selection of the temperature T a allows to form the glacial states at different micro-structure scales [16,18,23]: from a nano-structured state (for glacial states isothermally formed in a low-temperature range [210 K, 216 K]) to micro-structured state (for glacial states isothermally formed in a higher temperature range [218 K, 230 K]). Micro-structural investigations are very well adapted to the analysis of micro-structured glacial states in order to obtain detailed structural information on the long-range order inside crystallites of the glacial state and also on the short range order in the non-transformed supercooled liquid.…”