Structural phase transitions in crystals. II. Statistical analysis

Tomaszewski, Paweł E.

doi:10.1080/01411599208222900

Cited by 11 publications

(4 citation statements)

References 6 publications

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“…In most phase transitions, the higher-temperature phases have a higher symmetry than that of the low-temperature phases. , In acetonitrile, there are clear symmetry relations between phases α and β: the lattice translations are related (Figure ), and the 2 1 screw axis is common for both phases (parallel to axis b in phase α and to axis c in phase β). However, the point-group relation is not of the group−subgroup type, which is characteristic of second-order phase transitions of the Landau type; the first order of the phase transition is evident from the temperature hysteresis when the crystals were cooled and heated at isobaric conditions at 0.1 MPa; no volume change detected for isothermal compression of the sample at 0.63 GPa may indicate that the character of the phase transition is strongly pressure-dependent or that this pressure is higher than that at the tricritical point for acetonitrile.…”

Section: Resultsmentioning

confidence: 99%

Supramolecular Reaction between Pressure-Frozen Acetonitrile Phases α and β

Olejniczak

Katrusiak

2008

J. Phys. Chem. B

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The balance of weak CH...N bonds involving the H 3C- and -CN groups has been related to the structural rearrangement between centrosymmetric and polar acetonitrile structures. The linear highly polar molecules arrange antiparallel in phase alpha below a freezing temperature of 225 K/0.1 MPa and above a freezing pressure of 0.38(5) GPa/296 K and in a polar mode in phase beta below 206 K/0.1 MPa and at pressures higher than 0.63(5) GPa/296 K. The alpha <--> beta phase transition has been considered as a supramolecular reaction between 2-dimensional and 3-dimensional hydrogen-bonding networks, the latter favoring the polar association. Acetonitrile has been in situ pressure-frozen, and its structure has been determined at room temperature by single-crystal X-ray diffraction at 0.57(5), 0.63(5), and 1.50(5)GPa. The crystallization pressure at 296 K has been determined as 0.38(5) GPa both by ruby fluorescence in a diamond anvil-cell and by the compressibility measurement in a cylinder-and-piston device. Acetonitrile mixed with methanol trimerized at 1.60 GPa and 473 K yielding 4-amino-2,6-dimethylpyrimidine: it was in situ crystallized, and the structure of a single crystal, recovered at ambient conditions, was determined.

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Section: Resultsmentioning

confidence: 99%

Supramolecular Reaction between Pressure-Frozen Acetonitrile Phases α and β

Olejniczak

Katrusiak

2008

J. Phys. Chem. B

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“…Thus, in a general view, this phase transition may be regarded as one of the few examples where Landau's rule (only valid for continuous transitions) is not fulfilled. In a statistical analysis of documented phase transitions it has turned out that just for 10.4% of all transitions the HT phase has the lower symmetry …”

Section: Discussionmentioning

confidence: 99%

Crystal Structure and Chemical Bonding of the High-Temperature Phase of AgN₃

et al. 2007

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The crystal structure of silver azide (AgN3) in its high-temperature (HT) modification was determined from X-ray powder diffraction data, recorded at T = 170 degrees C and was further refined by the Rietveld method. The structure is monoclinic (P21/c (No. 14), a = 6.0756(2) A, b = 6.1663(2) A, c = 6.5729(2) A, beta = 114.19(0) degrees, V = 224.62(14) A3, Z = 4) and consists of two-dimensional Ag and N containing layers in which the silver atoms are coordinated by four nitrogen atoms exhibiting a distorted square coordination environment. These sheets are linked together by weaker perpendicular Ag-N contacts, thus forming a 4 + 2 coordination geometry around the silver atoms. The phase transition has been characterized by DTA, DSC, and measurement of the density, as well as of the ionic conductivity. Both, the room-temperature and the HT phase are electrically insulating. This fact is getting support by DFT band structure calculations within the generalized gradient approximation, using the PBE functional. On the basis of the DFT band structure, the bonding characteristics of both phases are essentially the same. Finally, the implication of the existence of a low-symmetry HT-phase in a crystalline explosive concerning decomposition mechanisms is discussed.

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“…There is a comprehensive review on ferroelectrics, including fluorides and oxyfluorides, by Ravez (2000); this follows an earlier review (Ravez 1986). Broader databases (1000 compounds) on phase transitions in crystals in general (including fluorides) are provided by Tomaszewski (1992aTomaszewski ( , 1992b.…”

Section: Reviewsmentioning

confidence: 99%