2021
DOI: 10.1038/s41598-021-97973-2
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Heat capacity anomalies of the molecular crystal 1-fluoro-adamantane at low temperatures

Abstract: Disorder–disorder phase transitions are rare in nature. Here, we present a comprehensive low-temperature experimental and theoretical study of the heat capacity and vibrational density of states of 1-fluoro-adamantane (C10H15F), an intriguing molecular crystal that presents a continuous disorder–disorder phase transition at T = 180 K and a low-temperature tetragonal phase that exhibits fractional fluorine occupancy. It is shown that fluorine occupancy disorder in the low-T phase of 1-fluoro-adamantane gives ri… Show more

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Cited by 10 publications
(12 citation statements)
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“…The disordered phase is most clearly observed in the dependences of both elastic moduli above T = 260 K. The LT-MT phase transition is not accompanied by a volume jump, but the MT-HT phase transition is manifested in a collapse of the volume less than 1%. Some discrepancy between our data on the phase transition temperatures and data from works 36,37 is explained by the presence of a low pressure of 0.05 GPa in our experimental chamber, which is necessary for acoustic contact with the sample.…”
Section: Resultscontrasting
confidence: 94%
See 1 more Smart Citation
“…The disordered phase is most clearly observed in the dependences of both elastic moduli above T = 260 K. The LT-MT phase transition is not accompanied by a volume jump, but the MT-HT phase transition is manifested in a collapse of the volume less than 1%. Some discrepancy between our data on the phase transition temperatures and data from works 36,37 is explained by the presence of a low pressure of 0.05 GPa in our experimental chamber, which is necessary for acoustic contact with the sample.…”
Section: Resultscontrasting
confidence: 94%
“…The volume jump (Fig. 1c) indicates that the HT -MT phase transition is a first-order transition, whereas the MT -LT transition is classified in works 36,37 as a second-order transition. It is interesting that the shear modulus of 1-fluoroadamantane increases stepwise successively in the HT -MT -LT transitions, whereas the bulk modulus in these transitions decreases successively.…”
Section: Resultsmentioning
confidence: 99%
“…It is worth emphasizing that a significant decrease in the heat flow and heat capacity was observed above the transition temperature T 1 (specific heat capacity, c p , is reduced by about 0.102 J·g −1 ·K −1 , Figure 2 ), which is consistent with the findings of Simões et al [ 16 ]. Such a decrease in heat capacity is usually explained by the increase in molecular order, typically occurring upon the crystallization of liquids or glasses.…”
Section: Resultssupporting
confidence: 90%
“…The lack of temperature hysteresis and the specific λ shape are signatures of second-order phase transitions, which usually accompany the order–disorder type of transitions [ 15 ], although a λ-transition has also been observed recently for a disorder–disorder transition in molecular crystals [ 16 ]. It is interesting to see that the measured Δ H values associated with both these transitions are rather low (Δ H = 1.13 and 0.46 kJ.mol −1 , at T 1 and T 2 , respectively), which is consistent with the exceptionally small changes of the unit–cell parameters upon both these phase transitions.…”
Section: Resultsmentioning
confidence: 99%
“…[2][3][4][5] Adamantane derivatives, conformationally rigid molecules, are examples of organic compounds displaying a rich polymorphism. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The pristine adamantane compound (C 10 H 16 ) is one of the most studied examples of organic molecular crystals which undergoes a first-order orderdisorder phase transition, from an ordered low-temperature phase (P4 ¯21 c, Z = 2) 21 to an orientationally disordered (OD) phase (Fm3 ¯m, Z = 4), which displays a translational facecentered cubic lattice with the center of masses of the molecules sitting at the lattice nodes but orientationally disordered. 22,23 Adamantane derivatives, with simple single 3692 | CrystEngComm, 2022, 24, 3692-3700 This journal is © The Royal Society of Chemistry 2022 a Grup de Caracteritzacio de Materials, Departament de Fisica and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politecnica de Catalunya, EEBE, Campus Diagonal-Besos, Av.…”
Section: Introductionmentioning
confidence: 99%