Search results for "Phase Transition"
showing 10 items of 1281 documents
Polymorphism and “reverse” spin transition in the spin crossover system [Co(4-terpyridone)2](CF3SO3)2·1H2O
2009
[EN] Compound [Co(4-terpyridone)(2)](CF3SO3)(2)center dot 1H(2)O, where 4-terpyridone is 2,6-bis(2-pyridyl)-4(1H)-pyridone, forms two polymorphs. Polymorph 1 displays a continuous spin conversion in the temperature region 300-120 K while polymorph 2 shows, on cooling, the onset of a continuous high-spin (HS) to low-spin (LS) conversion interrupted by an abrupt "reverse'' spin transition in the temperature region 217-203 K. The formed unstable HS intermediate phase (IP) undergoes a strong cooperative "normal'' spin transition characterised by a hysteresis loop 33 K wide. The structural data give support for a crystallographic phase transition, which takes place concomitantly with the "revers…
A liquid alkoxide precursor for the atomic layer deposition of aluminum oxide films
2020
For large-scale atomic layer deposition (ALD) of alumina, the most commonly used alkyl precursor trimethylaluminum poses safety issues due to its pyrophoric nature. In this work, the authors have investigated a liquid alkoxide, aluminum tri-sec-butoxide (ATSB), as a precursor for ALD deposition of alumina. ATSB is thermally stable and the liquid nature facilitates handling in a bubbler and potentially enables liquid injection toward upscaling. Both thermal and plasma enhanced ALD processes are investigated in a vacuum type reactor by using water, oxygen plasma, and water plasma as coreactants. All processes achieved ALD deposition at a growth rate of 1-1.4 angstrom/cycle for substrate tempe…
Determination of polymerization shrinkage stress by means of a photoelastic investigation
2002
This study examined the polymerization stress of different established composite resins (Tetric Ceram, Vivadent; EsthetX, Surefil, Dentsply/DeTrey; Clearfil AP-X, Clearfil Photo Posterior, Kuraray; Prodigy Condensable, sds Kerr; Filtek P 60, 3M ESPE; Solitaire 2, Heraeus-Kulzer) by means of a photo-elastic investigation and investigated six new, experimental composite resins, which have been claimed to exhibit less polymerization shrinkage (InTen-S, Vivadent; K 112, K 051, Dentsply/DeTrey; Compox, Pluto, Hermes 3M ESPE).Cylindrical cavities (phi 5 mm) in Araldit B epoxide resin plates (40 x 40 x 3 mm3) were pretreated with the Rocatec system to ensure bonding of the composite resin. Ten com…
η⇌μ exchange bonding mode of bidentate tmeda ligand. Molecular structure of [Y(tmhd)3]2(μ-tmeda)
2003
Abstract The reaction between the yttrium β-diketonate complexes Y(tmhd)3(H2O)x (x=0 or 1) and 0.5 or 1 equivalent of N,N,N′,N′-tetramethylethylenediamine (tmeda=Me2NCH2CH2NMe2) in hexane at room temperature afforded [Y(tmhd)3]2(tmeda) (1) and Y(tmhd)3(tmeda) (2) derivatives, respectively. They have been characterized by FT-IR, 1H NMR spectroscopy and by single crystal X-ray diffraction for 1. Variable temperature 1H NMR experiments indicated an equilibrium between 1 and 2. Their thermal behaviors were characterized by TGA and sublimation experiments. 2 is converted into compound 1 by heating over 100 °C. These precursors were used for the growth of Y2O3 and YBa2Cu3O7 − x films by pulsed in…
Optimization of sample preparation conditions for detecting trace amounts of β-tegafur in α- and β-tegafur mixture.
2012
We report a semiquantitative method for determining trace amounts (<1%) of thermodynamically stable forms in polymorphic mixtures, focusing on sample preparation ef- fects on solid phase transitions. Tegafur (5-fluoro-1-(oxolan-2-yl)-1,2,3,4-tetrahydropyrimidine- 2,4-dione) was used as a model material in this study. The amounts of the thermodynamically stable $ tegafur were increased to levels detectable by powder X-ray diffractometry by grind- ing the samples in a ball mill in the presence of water. The limit of detection for this method was as low as 0.0005% of $ tegafur in " and $ tegafur mixtures. The amount of $ tegafur after sample preparation was found to be proportional to the init…
Crystal structure of BaCa(CO3)2 alstonite carbonate and its phase stability upon compression
2021
Authors thank the financial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN) and the Agencia Estatal de Investigación under projects MALTA Consolider Ingenio 2010 network (MAT2015-71070- REDC) and PGC2018-097520-A-I00 (cofinanced by EU FEDER funds) and from the Generalitat Valenciana under project PROMETEO/2018/123. D.S.-P. and A.O.R. acknowledge the financial support of the Spanish MINECO for RyC-2014-15643 and RyC-2016-20301 Ramón y Cajal grants, respectively. C.P. acknowledges the financial support from the Spanish Ministerio de Economia y Competitividad (MINECO project FIS2017-83295-P). Authors also thank Dr. Nicolescu and the Mineralogy and Meteoritic…
Effect of pressure on the structural properties and electronic band structure of GaSe
2007
The structural properties of GaSe have been investigated up to 38 GPa by monochromatic X-ray diffraction. The onset of the phase transition from the e-GaSe to a disordered NaCi-type structural motif is observed near 21 GPa. Using the experimentally determined lattice parameters of the layered e-phase as input, constrained ab-initio total energy calculations were performed in order to optimize the internal structural parameters at different pressures. The results obtained for the nearest-neighbor Ga-Se distance agree with those derived from recent EXAFS measurements. In addition, information is obtained on the changes of Ga-Ga and Se-Se bond lengths which were not accessible to a direct expe…
Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6
2017
The ferroelectric to paraelectric phase transition of multiferroic ${\mathrm{CaMnTi}}_{2}{\mathrm{O}}_{6}$ has been investigated at high pressures and ambient temperature by second-harmonic generation (SHG), Raman spectroscopy, and powder and single-crystal x-ray diffraction. We have found that ${\mathrm{CaMnTi}}_{2}{\mathrm{O}}_{6}$ undergoes a pressure-induced structural phase transition ($P{4}_{2}mc\ensuremath{\rightarrow}P{4}_{2}/nmc$) at $\ensuremath{\sim}7\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ to the same paraelectric structure found at ambient pressure and ${T}_{c}=630\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The continuous linear decrease of the SHG intensity that disappears at 7 …
In situ high-pressure synchrotron X-ray diffraction study of the structural stability in NdVO4 and LaVO4
2014
Abstract Room-temperature angle-dispersive X-ray diffraction measurements on zircon-type NdVO 4 and monazite-type LaVO 4 were performed in a diamond-anvil cell up to 12 GPa. In NdVO 4 , we found evidence for a non-reversible pressure-induced structural phase transition from zircon to a monazite-type structure at 6.5 GPa. Monazite-type LaVO 4 also exhibits a phase transition but at 8.6 GPa. In this case the transition is reversible and isomorphic. In both compounds the pressure induced transitions involve a large volume collapse. Finally, the equations of state and axial compressibilities for the low-pressure phases are also determined.
High-pressure powder x-ray diffraction study of EuVO4
2015
The high-pressure structural behavior of europium orthovanadate has been studied using in-situ, synchrotron based, high-pressure x-ray powder diffraction technique. Angle-dispersive x-ray diffraction measurements were carried out at room temperature up to 34.7 GPa using a diamond-anvil cell, extending the pressure range reported in previous experiments. We confirmed the occurrence of zircon-scheelite phase transition at 6.8 GPa and the coexistence of low- and high-pressure phases up to 10.1 GPa. In addition, clear evidence of a scheelite-fregusonite transition is found at 23.4 GPa. The fergusonite structure remains stable up to 34.7 GPa, the highest pressure reached in the present measureme…