Thickness Effect on Thermal Stability by Phase Transition of Single Crystal Hematite Nanorings

NANO ◽  
2015 ◽  
Vol 10 (06) ◽  
pp. 1550084
Author(s):  
Le Li ◽  
Fagen Li ◽  
XiaoPing Zhang ◽  
Jun Wang
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Thermal Stability ◽  
Single Crystal ◽  
Magnetic Measurements ◽  
Magnetic Measurement ◽  
High Vacuum ◽  
Finite Size ◽  
Thickness Effect ◽  
Temperature Phase

Single-crystal hematite (α- Fe 2 O 3) nanorings with three different thicknesses were synthesized by a hydrothermal method. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) show that the nanorings are single-crystal and have relatively uniform outer diameters of 160nm, and heights of about 100nm. Magnetic measurements up to 920K have been performed on hydrothermally synthesized α- Fe 2 O 3 nanorings and nanoparticles using a quantum design vibrating sample magnetometer. A high temperature phase transition of thermal stability (α- Fe 2 O 3 to Fe 3 O 4) occurs when magnetic measurement was performed under high vacuum (< 9.5 × 10-5 Torr). The phase transition temperature is 670K for nanorings with thickness of ∼30nm, 718K for nanorings with thickness of ∼50nm, 678K for nanorings with thickness of ∼65nm, and 640K for ∼35nm nanoparticles. This data show better thermal stability of nanorings with the thickness of ∼50nm than the other two kinds of nanoring samples The Néel temperature (T N ) of α- Fe 2 O 3 nanorings with the thickness of ∼50nm is determined to be 937.2K by magnetic measurement for the first time, about 22.8K below the bulk value. The small reduction of the T N of the α- Fe 2 O 3 nanorings is consistent with the finite-size scaling theory.

scholarly journals Phase transition and proton ordering at 50 K in 3-(pyridin-4-yl)pentane-2,4-dione

2017 ◽  
Vol 73 (6) ◽  
pp. 1172-1178 ◽  
Author(s):  
Khai-Nghi Truong ◽  
Carina Merkens ◽  
Martin Meven ◽  
Björn Faßbänder ◽  
Richard Dronskowski ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Single Crystal ◽  
Structural Phase ◽  
Pyridyl Ring ◽  
Temperature Phase ◽  
Crystallographic Axis ◽  
Temperature Phase Transition ◽  
Intramolecular Hydrogen ◽  
Low Temperature Phase

Single-crystal neutron diffraction experiments at 100 and 2.5 K have been performed to determine the structure of 3-(pyridin-4-yl)pentane-2,4-dione (HacacPy) with respect to its protonation pattern and to monitor a low-temperature phase transition. Solid HacacPy exists as the enol tautomer with a short intramolecular hydrogen bond. At 100 K, its donor···acceptor distance is 2.450 (8) Å and the compound adopts space group C2/c, with the N and para-C atoms of the pyridyl ring and the central C of the acetylacetone substituent on the twofold crystallographic axis. As a consequence of the axial symmetry, the bridging hydrogen is disordered over two symmetrically equivalent positions, and the carbon–oxygen bond distances adopt intermediate values between single and double bonds. Upon cooling, a structural phase transition to the t 2 subgroup P\bar 1 occurs; the resulting twins show an ordered acetylacetone moiety. The phase transition is fully reversible but associated with an appreciable hysteresis in the large single crystal under study: transition to the low-temperature phase requires several hours at 2.5 K and heating to 80 K is required to revert the transformation. No significant hysteresis is observed in a powder sample, in agreement with the second-order nature of the phase transition.

Thermal Stability of CoSi2 on Single Crystal and Polycrystalline Silicon

1990 ◽  
Vol 182 ◽  
Author(s):  
J. R. Phillips ◽  
P. Revesz ◽  
J. O. Olowolafe ◽  
J. W. Mayer
Keyword(s):  
Electron Microscopy ◽  
Thermal Stability ◽  
Single Crystal ◽  
Polycrystalline Silicon ◽  
Sheet Resistivity ◽  
X Ray ◽  
Resistivity Measurements ◽  
Silicide Layer ◽  
Thermal Stability Of ◽  
Scanning Electron

AbstractThe thermal stability of Co silicide on single crystal and polycrystalline Si has been investigated. Co films were evaporated onto (100) Si and undoped polycrystalline Si and annealed in vacuum. Resulting silicide films were examined using Rutherford backscattering spectroscopy, scanning electron microscopy, electron—induced x—ray spectroscopy, and sheet resistivity measurements. We find that CoSi2 on single crystal (100) Si remains stable through 1000ºC. In contact with undoped polycrystalline Si, intermixing begins at temperatures as low as 650ºC for 30min annealing. The Co silicide and Si layers are intermixed after 750ºC 30min annealing, giving islands of Si surrounded by silicide material, with both components extending from the surface down to the underlying oxide layer. The behavior of CoSi2 contrasts with results reported for TiSi2 which agglomerates on single crystal Si around 900ºC but is stable on polycrystalline silicon as high as 800ºC. Resistivity measurements show that the Co silicide remained interconnected despite massive incursion by Si into the silicide layer.

A temperature-induced order–disorder phase transition in a 4-substituted 4,2′:6′,4′′-terpyridine

2015 ◽  
Vol 71 (6) ◽  
pp. 805-813 ◽  
Author(s):  
Juan Granifo ◽  
Marleen Westermeyer ◽  
Maricel Riquelme ◽  
Rubén Gaviño ◽  
Sebastián Suárez ◽  
...  
Keyword(s):  
Phase Transition ◽  
Single Crystal ◽  
Single Molecule ◽  
Temperature Phase ◽  
Asymmetric Unit ◽  
Phase Form ◽  
Space Group ◽  
Cell Parameters ◽  
Disorder Phase Transition ◽  
First Order

Crystals of 4′-(isoquinolin-4-yl)-4,2′:6′,4′′-terpyridine (iqtp), C24H16N4, grown from an ethanol solution, undergo a reversible first-order single-crystal to single-crystal phase transition at T c in the range 273–275 K, from a disordered higher-temperature phase [form (I)] in the space group P21/c, with one single molecule in the asymmetric unit, to an ordered lower-temperature one [form (II)] in the space group P21/n, with two independent molecules in the asymmetric unit. There is a group–subgroup relationship linking (I)–(II), due to cell doubling and the disappearance of a number of symmetry operations. In addition to X-ray diffraction, the transition has been monitored by Raman spectroscopy and differential scanning calorimetry, the latter disclosing an enthalpy change of 0.72 (6) kJ mol−1. Variations of the unit-cell parameters with temperature between 170 and 293 K are presented. The evolution of diffraction spots in the vicinity of the transition temperature shows the coexistence of both phases, confirming the first-order character of the transition. Structural details of both phases are analyzed and intermolecular interactions compared in order to investigate the mechanism of the phase transition. A three-dimensional Hirshfeld surface analysis was performed to corroborate the significant changes in the intermolecular features.

Stress-induced structures on surfaces observed using Scanning Tunneling Microscopy and low-energy Electron Microscopy

1992 ◽  
Vol 50 (1) ◽  
pp. 332-333
Author(s):  
Ellen D. Williams ◽  
R.J. Phaneuf ◽  
N.C. Bartelt ◽  
W. Swiech ◽  
E. Bauer
Keyword(s):  
Electron Microscopy ◽  
Surface Morphology ◽  
Scanning Tunneling Microscopy ◽  
High Vacuum ◽  
Finite Size ◽  
Low Energy ◽  
Energy Electron ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Low Energy Electron

Elastic stresses play a well-known and important role in the structure of thin films during growth. However, elastic effects can also greatly influence surface morphology of the substrate. One source of this influence, as has long been recognized is the elastic interactions between steps on surfaces. More recently, Marchenko has shown that surface stress can stabilize finite-size structures in surfaces, such as facets. Traditionally surface morphologies such as steps and facets have been measured by low-energy electron diffraction. However, the more recent development of ultra-high vacuum compatible microscopic techniques such as scanning tunneling microscopy, reflection electron microscopy, and low-energy electron microscopy, now make it possible to image steps and facets directly to obtain information about sizes and size distributions. This information in turn makes it possible to test the influence of stress on surface morphology directly.

Temperature-induced first-order displacive phase transition of isonicotinamide-4-methoxybenzoic acid co-crystal

2017 ◽  
Vol 73 (2) ◽  
pp. 285-295 ◽  
Author(s):  
Tze Shyang Chia ◽  
Ching Kheng Quah
Keyword(s):  
Phase Transition ◽  
Single Crystal ◽  
Variable Temperature ◽  
Structural Phase ◽  
Differential Scanning Calorimetry Measurement ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
First Order ◽  
Displacive Phase Transition ◽  
Methoxybenzoic Acid

Isonicotinamide–4-methoxybenzoic acid co-crystal (1), C6H6N2O·C8H8O3, is formed through slow evaporation from methanol solution and it undergoes a first-order isosymmetry (monoclinicI2/a↔ monoclinicI2/a) structural phase transition atTc= 142.5 (5) K, which has been confirmed by an abrupt jump of crystallographic interaxial angle β from variable-temperature single-crystal XRD and small heat hysteresis (6.25 K) in differential scanning calorimetry measurement. The three-dimensional X-ray crystal structures of (1) at the low-temperature phase (LTP) (100, 140 and 142 K) and the high-temperature phase (HTP) (143, 150, 200, 250 and 300 K) were solved and refined as a simple non-disordered model with finalR[F2> 2σ(F2)] ≃ 0.05. The asymmetric unit of (1) consists of crystallographically independent 4-methoxybenzoic acid (A) and isonicotinamide (B) molecules in both enantiotropic phases. MoleculeAadopts a `near-hydroxyl' conformation in which the hydroxyl and methoxy groups are positioned on the same side. Both `near-hydroxyl' and `near-carbonyl' molecular conformations possess minimum conformational energies with an energy difference of < 0.15 kJ mol−1from a potential energy surface scan. In the crystal, molecules are joined into linearABBAarrays by intermolecular N—H...O and O—H...N hydrogen bonds which were preserved in both phases. However, theseABBAarrays are displaced from planarity upon LTP-to-HTP transition and the changes in inter-array interactions are observed in two-dimensional fingerprint plots of their Hirshfeld surfaces. ThePIXELenergies of each molecular pair in both phases were calculated to investigate the difference in intermolecular interaction energies before and after the displacement ofABBAarrays from planarity, which directly leads to the single-crystal-to-single-crystal phase transition of (1).

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