On the sequence of three related phases of [Ni(H2O)2(15-crown-5)](HSO4)2 in the temperature range 110–295 K

2010 ◽  
Vol 66 (4) ◽  
pp. 430-440 ◽  
Author(s):  
Maxime A. Siegler ◽  
Eli Stavitski
Keyword(s):  
Structural Changes ◽  
Crystal Packing ◽  
Solid Phase ◽  
Significant Loss ◽  
Phase Iii ◽  
Temperature Phase ◽  
Phase Sequence ◽  
Analogous Compound ◽  
Low Temperature Phase ◽  
Degree Of Order

Attempts to prepare the compound [Ni(H2O)2(15-crown-5)](X)2 were eventually successful with X = NO_3^- provided that a synthetic route aimed at restricting water was followed. Application of this method was extended to make the analogous compound with X = HSO_4^-, for which three symmetry-related phases were isolated between 295 and 110 K: a room-temperature phase with Z′ = ½ [phase (I)], an intermediate-temperature phase with Z′ = 1 [phase (II)] and a low-temperature phase with Z′ = 2 [phase (III)]. The phases are related by two reversible solid–solid phase transitions, and both transitions take place without a significant loss of crystallinity. In the phase sequence (I) ↔ (II) ↔ (III) (Z′: ½ ↔ 1 ↔ 2), the crystal packing remains remarkably similar but the degree of order in the crystal changes significantly; the structure is very disordered at room and intermediate temperatures but is ordered at 110 K. The compound [Ni(H2O)2(15-crown-5)](HSO4)2 has a complicated hydrogen-bonding network, which contains O—H...O bonds between the counterions. Structural changes are largest along some face-diagonal directions in the sequence (I) ↔ (II) ↔ (III).

Formation process of periodic non-conservative antiphase boundary structure in L-Pd5Ce

1990 ◽  
Vol 48 (4) ◽  
pp. 162-163
Author(s):  
Masaru Itakura ◽  
Noriyuki Kuwano ◽  
Kensuke Oki
Keyword(s):  
Formation Process ◽  
Domain Size ◽  
Antiphase Boundary ◽  
Boundary Structure ◽  
Temperature Phase ◽  
Arc Melting ◽  
Iced Water ◽  
Antiphase Domains ◽  
Low Temperature Phase ◽  
Degree Of Order

The low temperature phase of Pd5Ce (L-Pd5Ce) has a one-dimensional long period superstructure (1D-LPS) derived from Ll2. The periodic antiphase boundaries (APBs) are parallel to (110) planes and have a shift vector of 1/2[110]. Hereafter, the indices are referred to the basic lattices of Ll2 As insertion of the APB causes a change in composition, such an APB is called “non-conservative”. Then, a domain size M depends upon the Ce concentration in the alloy. It was found that M increases also with temperature. The temperature dependency of M is attributed to a change of the degree of order within the antiphase domains. In this work, morphology of the non-conservative APBs is observed to clarify the formation process of the 1D-LPS.The alloy of Pd-16.7 at%Ce was prepared by arc melting in argon atmosphere. Disc specimens made from the alloy ingot were first held at 985 K for 260 ks and quenched in iced water to obtain the state of M=∞ or Ll2, followed by annealing for various lengths of time. The annealing temperature was 873 K where the equilibrium value for M is about 3 in unit of (110) lattice spacing of Ll2. Observation was carried out using microscopes JEM-2000FX, JEM-4000EX (HVEM Lab., Kyushu Univ.) and JEM-2000EX (Dept. of Mater. Sci. Tech., Kyushu Univ.).

Molecular dynamics simulation of the phase transition in adamantane

1988 ◽  
Vol 66 (4) ◽  
pp. 1018-1025 ◽  
Author(s):  
A. S. Trew ◽  
G. S. Pawley
Keyword(s):  
Orientational Order ◽  
Significant Degree ◽  
Phase Changes ◽  
Dynamics Simulation ◽  
Local Order ◽  
Temperature Phase ◽  
Orientational Distribution ◽  
Molecule Model ◽  
Low Temperature Phase ◽  
Degree Of Order

Phase changes in adamantane have been studied by MD simulation on the DAP computers, using a zero-pressure technique to simulate clusters of 128 and 256 molecules where each member interacts with all others via the rigid molecule model and the 6-exp atom–atom potential. The form of the potential has been modified to permit the use of the 16 hydrogen sites only, giving a 65% saving in the calculation times. This model is shown to give lattice dynamics of adamantane closely similar to results with potentials which are generally accepted.Using this potential the system equilibrates into the correct low temperature phase [Formula: see text] and on heating, a transition is observed at 210 ± 10 K to an Fm3m phase where the molecules lie preferentially in the Td orientations, as expected. Further heating beyond 240 ± 15 K removes all apparent orientational order, though the underlying lattice is still fcc. On recooling the cluster from 300 to 100 K the orientational distribution function developed a significant degree of order as determined through the calculation of a correlation function designed to show any local order. This order is consistent with the lowest phase structure, but would in itself be insufficient to suggest a particular crystal structure.

The low-temperature phase III structure and phase transition behaviour of cyclohexanone

2006 ◽  
Vol 62 (4) ◽  
pp. 592-598 ◽  
Author(s):  
Richard M. Ibberson
Keyword(s):  
Phase Ii ◽  
Ambient Pressure ◽  
Isotope Effects ◽  
Orthorhombic Phase ◽  
Phase Behaviour ◽  
Phase Iii ◽  
Temperature Phase ◽  
Space Group ◽  
Low Temperature Phase ◽  
Transition Behaviour

The crystal structure of phase III of perdeuterocyclohexanone, C6D10O, has been determined at 5 K using high-resolution neutron powder diffraction. Below its melting point of 245 K cyclohexanone forms a plastic crystal in the space group Fm\bar 3m. On cooling below 225 K the crystal transforms to the monoclinic phase III structure in the space group P21/n. The orthorhombic phase II structure exists under high pressure, but the triple point for all three phases is close to atmospheric pressure. Details of the phase II structure are also reported at 4.8 kbar (273 K) and ambient pressure. The phase behaviour of the compound and isotope effects are discussed.

scholarly journals Low temperature phase transition and structure of CsMgPO4

2014 ◽  
Vol 70 (a1) ◽  
pp. C68-C68
Author(s):  
Maria Orlova ◽  
Lukas Perfler ◽  
Dmitriy Michailov ◽  
Albina Orlova ◽  
Sergei Khainakov ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Structural Changes ◽  
Temperature Phase ◽  
Ambient Conditions ◽  
Monoclinic Modification ◽  
Synchrotron Powder Diffraction ◽  
Orthorhombic Modification ◽  
Temperature Phase Transition ◽  
Low Temperature Phase

CsMgPO4 doped in radioisotopes is a promising compound for usage as a radioactive medical source. However, a low temperature phase transition at the temperatures close to ambient conditions (-370C) was observed. Information about structural changes is important in order to understand whether it can cause any problem for medical use of this compound. Structural changes have been investigated in detail using synchrotron powder diffraction methods, Raman spectroscopy and DFT calculations. The structure undergoes transformation from orthorhombic modification, sp. gr. Pnma (RT phase) to monoclinic modification, sp.gr P21/n (LT phase). New LT modification adopts similar to RT but slightly distorted unit cell: a=9.58199(2)Å, b=8.95501(1) Å, c=5.50344(2)Å, β=90.68583(1)0, V=472.198(3) Å3. The framework is made up of alternating magnesia and phosphate tetrahedra sharing vertices with caesium counter cations located in the channels formed. Upon the transformation a combined rotation of PO4 and MgO4 tetrahedral takes place. A comparison with other phase transition in ABW-type framework class compounds is given.

scholarly journals NQR and Phase Transitions in Hexachlorocyclopropane Crystal

1990 ◽  
Vol 45 (3-4) ◽  
pp. 339-342 ◽  
Author(s):  
Masahiko Suhara ◽  
Koichi Mano
Keyword(s):  
Phase Transitions ◽  
Slow Rate ◽  
Metastable Phase ◽  
Phase Iii ◽  
Temperature Phase ◽  
Dsc Studies ◽  
Disordered Phase ◽  
Solid Phases ◽  
Low Temperature Phase ◽  
Phase Phase

Abstract35Cl NQR and DSC studies on phase transitions in hexachlorocyclopropane (HCCP), C3Cl6 , are reported. It is found that HCCP has three solid phases: A high temperature disordered phase (Phase I) above 301 K (no NQR spectrum was observed); a metastable phase (Phase II), which exhibited 6 NQR lines from 77 to 270 K; a low temperature phase (Phase III) in which a 24-multiplet of 35Cl NQR lines at 77 K, the most complex multiplet spectrum ever reported was observed. DSC measurement shows a A-type transition at 301 K and a broad transition of very slow rate at 285 K. The structure and mechanism of phase transitions in HCCP crystal are discussed.

An ESR Study of Structural Phase Transitions of(NH4)2Pb[Cu(NO2)6]

1986 ◽  
Vol 41 (9) ◽  
pp. 1154-1158 ◽  
Author(s):  
Tetsuo Asaji ◽  
Laxman Shrikrishna Prabhumirashi ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transitions ◽  
Structural Changes ◽  
Structural Phase ◽  
Esr Spectra ◽  
Phase Iii ◽  
Temperature Phase ◽  
Intermediate Phases ◽  
Temperature Phase Transition ◽  
G Value ◽  
Phase Iv

The structural changes of (NH4)2Pb[Cu(NO2)6] crystals during the phase transitions at 316, 287, and 95 K were studied by means of a single crystal ESR technique. Anisotropic g values [g∥ > g⊥) were obtained in the lowest temperature phase IV, whereas the ESR spectra recorded in the intermediate phases III and II, in which the crystal is known to be tetragonally compressed along the c axis, could be interpreted by use of effective g values [g(∥c) < g(⊥c)]. In the highest temperature phase I an isotropic g value was obtained. The phases I, II, and III o f the present complex can be assumed to be very similar to the corresponding phases observed above ~ 250 K for the compounds R2Pb[Cu(NO2)6] with R = K, Rb, Cs, and Tl. However, the lowest temperature phase transition transforms the phase III with an antiferrodistortive order of the elongated [Cu(NO2)6]4- octahedra into the phase IV with a ferrodistortive one. This occurs only for the complex with R = NH4 and is very unusual. The results of the 14N NQR experiments already reported for the phases III and IV could be well explained by the present newly proposed model.

Effect of temperature and phase on the photoionization energy threshold of TMPD in hydrocarbon solvents

1977 ◽  
Vol 55 (11) ◽  
pp. 1821-1831 ◽  
Author(s):  
J. Bullot ◽  
M. Gauthier
Keyword(s):  
Liquid Phase ◽  
Low Temperature ◽  
Temperature Dependence ◽  
Solid Phase ◽  
Energy Threshold ◽  
Effect Of Temperature ◽  
Temperature Phase ◽  
Recombination Luminescence ◽  
Hydrocarbon Solvents ◽  
Low Temperature Phase

The temperature dependence of the TMPD photoionization energy threshold, I, in a set of eight hydrocarbon solvents has been systematically studied, from room temperature down to 77 K. For this purpose ion-pair formation is detected either by measuring the photocurrents in the liquid phase or by measuring the recombination luminescence intensity in the solid phase. It is found that I(liquid) increases linearly when the temperature is decreased down to the liquid–solid transition temperature. At this temperature I undergoes an abrupt increase of 0.2–0.6 eV depending on the hydrocarbon and the nature of the phase transition. Any subsequent solid–solid phase change is accompanied by a new shift towards higher energy. In the low temperature phase of all the studied crystals, I(solid) has a constant value down to 77 K. Glass-forming liquids have a very different behavior: I varies linearly in the liquid and the straight line extrapolates to the I(glass) value at 77 K. The applicability of the two methods is discussed. From the present data it is concluded that the conduction state energy, V0, is constant in the low-temperature phase of crystals. By calculating the polarization energy due to the TMPD+ cation and from data on the temperature dependence of V0 in the liquid phase, we have estimated V0 in crystalline n-hexane (0.64 eV) and 2,2,4-trimethylpentane (0.44 eV) and in the plastic phase of cyclohexane (0.47 eV) and 2,2-dimethylbutane (0.01 eV). Finally a correlation of I with the medium density is described.

Pseudo-symmetries of the Phases of (Et4N)2ZnBr4

2000 ◽  
Vol 55 (9-10) ◽  
pp. 801-809 ◽  
Author(s):  
P. Sondergeld ◽  
H. Fuess ◽  
S. A. Mason ◽  
H. Ishihara ◽  
W. W. Schmahl
Keyword(s):  
Room Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Rays ◽  
Heavy Atoms ◽  
Tetragonal Crystal ◽  
Phase Sequence ◽  
Decomposition Point ◽  
Tetragonal Crystal System ◽  
Low Temperature Phase

Abstract The phase sequence of (Et4N)2ZnBr4 has been determined based on thermal analysis. Below the decomposition point (572 K) four phases are distinguished. The structures of three of the phases have been determined from 4-circle diffraction data at 240 (neu-trons), 299 and 373 K (X-rays), respectively. The multiply twinned low-temperature phase (at 240 K) is characterized by a pseudo-orthorhombic lattice (monoclinic, Plal, a = 17.6120(9] Å, b = 8.8195(4) Å, c = 16.1062(6) Å and ß=89.94(2)°), whereas the room-temperature phase (299 K:P421c, a = 8.9874(6)Åand c = 15.9774 Å) and the first high-temperature phase (373 K: P42 /nmc, a= 9.145(4) Å and c = 15.835(8) Å) belong to the tetragonal crystal system. The transitions between the three phases are essen-tially connected with a stepwise ordering of the Et4N+ ions, whereas the positions of the heavy atoms change only slightly. Three 81Br NQR lines are observed between 77 and 204 K.

scholarly journals Bulk and Surface Low Temperature Phase Transitions in the Mg-Alloy EZ33A

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1127
Author(s):  
Alexander Straumal ◽  
Ivan Mazilkin ◽  
Kristina Tzoy ◽  
Boris Straumal ◽  
Krzysztof Bryła ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Low Temperature ◽  
Grain Boundary ◽  
Solid Phase ◽  
Cast Alloy ◽  
Wetting Transition ◽  
Temperature Phase ◽  
Grain Boundary Wetting ◽  
Structure Assessment ◽  
Low Temperature Phase

Low-temperature phase transitions in the EZ33A Mg-cast alloy have been investigated. Based on the structure assessment of the alloy after annealing at 150 °C (1826 h) and at 200 °C (2371 h) a grain boundary wetting transition by a second solid phase was documented. Within a 50 °C temperature range, substantial differences in the α(Mg) grain boundary fraction wetted by the (Mg,Zn)12RE intermetallic were observed. In contrast to what was reported in the literature, two different types of precipitates were found within α(Mg) grains. With increasing annealing temperatures, both types of precipitates dissolved.

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