Pressure induced phase transitions in hydroquinone.
ABSTRACT High pressure behavior of alpha-hydroquinone (1,4-dihydroxybenzene) has been studied using Raman spectroscopy up to pressures of 19 GPa. Evolution of Raman spectra suggests two transitions around 3.3 and 12.0 GPa. The first transition appears to be associated with the lowering of crystal symmetry. Above 12.0 GPa, Raman bands in the internal modes region exhibit continuous broadening suggesting that the system is progressively evolving into a disordered state. This disorder is understood as arising due to distortion of the hydrogen-bonded cage across the second transition around 12 GPa.
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ABSTRACT: The high pressure compression behaviors of two hydroquinone compounds have been investigated using a combination of in situ synchrotron x-ray powder diffraction and Raman spectroscopy up to ca. 7 GPa. The structural integrity of the α-form hydroquinone clathrate is maintained throughout the pressure range, whereas the CH4-loaded β-form hydroquinone clathrate decomposes and transforms to a new high pressure phase near 5 GPa. The bulk modulus (K) and its pressure derivative (K′) of the α-form and the CH4-loaded β-form hydroquinones are measured to be 8.2(3) GPa and 8.4(4), and 10(1) GPa and 9(2), respectively, representing one of the most compressible classes of crystalline solids reported in the literature. The corresponding axial compression behaviors, however, show greater contrast between the two hydroquinone compounds; the elastic anisotropy of the α-form is only marginal, being K(a):K(c) = 1.08:1, whereas that of the CH4-loaded β-form is rather drastic, being K(a):K(c) = 11.8:1. This is attributed to the different dimensionality of the hydrogen bonding networks between the two structures and might in turn explain the observed structural instability of the β-form, compared to the α-form.The Journal of Chemical Physics 03/2009; 130(12):124511-124511-6. · 3.12 Impact Factor
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ABSTRACT: Pressure-induced transformation of γ-IMC [1-(p-chlorobenzoyl)-5-methoxy-2-methylindole-3-acetic acid] is analyzed from Raman scattering investigations in the low-frequency range of 10–250 cm−1 and the high frequency region between 1550 and 1750 cm−1, where CO stretching vibrations are usually observed. At room temperature, by pressurization from atmospheric pressure up to 4 GPa, γ-IMC undergoes a collapse transformation into a high-pressure crystalline form, induced by large rearrangement in the hydrogen-bonded network associated with molecular conformational changes. The Raman spectrum of the high-pressure crystal is similar to that of the α form, which is denser than the γ form and metastable with respect to γ-IMC at atmospheric pressure. Upon further compression a solid-state amorphization is observed via the breakdown of hydrogen bonds. The Raman line shape of the high-pressure amorphous form is different from that of the vitreous state (or thermal glass obtained by quenching the liquid), suggesting the existence of a high-density amorphous state. By release of pressure, this high-density amorphous state transforms into the thermal glass. This transformation can be interpreted as a transformation between a high-density amorphous to a low-density amorphous state, which could be associated with a polyamorphic transformation.Physical review. B, Condensed matter 01/2008; 77(9). · 3.77 Impact Factor