Abstract
Phase transitions in the crystalline state of chiral sorbose were examined using precise heat capacity calorimetry and X-ray crystallography. The calorimetry established heat capacity below room temperature. Besides the known transition (main transition) at 199.5 K, the calorimetry detected plural thermal anomalies assignable to new phase transitions (around 210 K) and a glass transition (at ca. 120 K). The X-ray diffraction at low temperatures established the crystal structure of the lowest temperature phase. The identification of the broken symmetry upon the main transition solves an apparent contradiction that the structural disorder reported previously does not contribute seemingly to the symmetrization.
Highlights
Phase transition has long been a central issue in the science of matter [1,2]
After the description of the experiments (Section 2), we describe the experimental results of the calorimetry (Sections 3.1 and 3.2) and crystallographic experiments of the high (Section 3.3) and low temperature (Section 3.4) phases in this order
The difference reflected the improvement of the adiabatic heat capacity calorimetry
Summary
Phase transition has long been a central issue in the science of matter [1,2]. Molecular crystals have offered essential examples where molecular dynamics bring about intrinsic phase transitions from nominally perfect crystals into partially disordered states such as plastic crystals and liquid crystals [4]. In contrast to the understanding of phase transitions as the way of acquiring disorder (entropy) in the previous sentence, there exists a counter view, the emergence of order. In the latter context, the concept of “spontaneous symmetry-breaking” was one of the essentials reached in the past [5]. The ensemble undergoes the so-called order-disorder transition into an ordered phase, in which the number of one orientation, Crystals 2020, 10, 361; doi:10.3390/cryst10050361 www.mdpi.com/journal/crystals
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