Changes in the structure of the 1:2 complex of N-ethyl-N-methylmorpholinium and 7,7,8,8-tetracyano-p-quinodimethane, MEM(TCNQ)2, above room temperature. II. Determination of the structure (above the phase transition)at 348 K

1981 ◽  
Vol 37 (4) ◽  
pp. 863-868 ◽  
Author(s):  
B. van Bodegom ◽  
A. Bosch
Keyword(s):  
Phase Transition ◽  
Room Temperature

scholarly journals Crystalline forms of silver iodide II: Determination of phase transformations

2007 ◽  
Vol 72 (8-9) ◽  
pp. 857-868 ◽  
Author(s):  
Marija Vukic ◽  
Dragan Veselinovic ◽  
Vesna Markovic
Keyword(s):  
Phase Transition ◽  
Phase Transformations ◽  
Heating Rate ◽  
Silver Iodide ◽  
Room Temperature ◽  
Sample Heating ◽  
Crystalline Forms

In order to obtain appropriate forms of AgI (?- and ?-), a procedure was developed to synthesize AgI at room temperature (23?C), whereby samples of varying crystallographic purity and of varying crystallographic contents of the different forms were obtained. This paper presents the results of investigations of the influence of the manner of preparation of ?-AgI and ?-AgI samples and the sample heating rate on the phase transformations and their temperatures. During the heating of non-ground, ground and pressed synthesized AgI samples, the phase transformations and the corresponding temperatures for one ?-AgI and four ?-AgI samples with different ?-AgI contents (representing a crystallographic impurity) were identified. The following phase transformations were observed for the non-ground AgI samples: ?-AgI ? ?-AgI at 149.6?C (for the ?-AgI sample) and ?-AgI ? ?-AgI at 148.7?C or 148.2?C for the ?-AgI samples with a minimum content of ?-AgI (less than 7 %), as a crystallographic impurity. The phase transition ?-AgI ? ?-AgI was irreversible because ?-AgI was obtained whenever the samples were heated up to 260?C. Manual sample grinding, as well as pressing at p1 = 650 MPa and p2 = 900 MPa resulted in the ?-AgI ? ?-AgI phase transition in all the investigated cases. .

Photoacoustic determination of phase transition in BaTiO3 induced by high pressure at room temperature

2003 ◽  
Vol 74 (1) ◽  
pp. 732-734 ◽  
Author(s):  
M. Villagrán-Muniz ◽  
M. Navarrete ◽  
E. V. Mejı́a-Uriarte
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Room Temperature

Phase Transition in K3Na(MoO4)2 and Determination of the Twinned Structures of K3Na(MoO4)2 and K2.5Na1.5(MoO4)2 at Room Temperature

1997 ◽  
Vol 53 (4) ◽  
pp. 596-603 ◽  
Author(s):  
J. Fábry ◽  
V. Petrícek ◽  
P. Vanek ◽  
I. Císarová
Keyword(s):  
Phase Transition ◽  
Room Temperature ◽  
Domain Switching ◽  
Point Group ◽  
Atomic Displacement ◽  
Scanning Calorimetry ◽  
Sodium Potassium ◽  
Displacement Vectors ◽  
Reversible Phase Transition

The room-temperature phases of sodium potassium molybdates K3Na(MoO4)2 and K2.5Na1.5(MoO4)2 are isostructural with the monoclinic low-temperature phases of KaNa(SeO4)2 and K3Na(CrO4)2, which are twinned distorted glaserite structures. In the molybdates there are two crystallographically independent potassiums and their environment slightly differs from those in K3Na(SeO4)2 and K3Na(CrO4)2. The excessive Na in K2.5Na1.5(MoO4)2 occupies the position of the more firmly bound potassium. A reversible phase transition at 513 K was discovered in KaNa(MoO4)2 by DSC (differential scanning calorimetry), but no such transition in K2.5Na1.5(MoO4)2 was detected. Both samples used in the diffractometer experiment were found to be composed of six domains being related by twinning operations of the point group 6. The twinning may be considered as a combination of a merohedral and a pseudo-merohedral twinning with two- and threefold rotations as twinning operations, respectively. However, a reversible domain switching, which is observable in the related ferroelastic crystals of KaNa(SeO4)2 and K3Na(CrO4)2, was not observed either in K3Na(MoO4)2 or in K2.5Na1.5(MoO4)2, either due to semitransparency of the samples or high ferroelastic distortion. This distortion is manifested by the values of the atomic displacement vectors which are about twice as large as those in the selenate or the chromate.

Interactions Between Al and Cr Thin Films

1976 ◽  
Vol 34 ◽  
pp. 638-639
Author(s):  
R. M. Anderson ◽  
T. M. Reith ◽  
M. J. Sullivan ◽  
E. K. Brandis
Keyword(s):  
Thin Films ◽  
Room Temperature ◽  
Vacuum System ◽  
Processing Temperature ◽  
Diffusion Couples ◽  
Electronic Circuits ◽  
Intermetallic Formation ◽  
Si Substrates ◽  
Aluminum Silicon

Thin films of aluminum or aluminum-silicon can be used in conjunction with thin films of chromium in integrated electronic circuits. For some applications, these films exhibit undesirable reactions; in particular, intermetallic formation below 500 C must be inhibited or prevented. The Al films, being the principal current carriers in interconnective metal applications, are usually much thicker than the Cr; so one might expect Al-rich intermetallics to form when the processing temperature goes out of control. Unfortunately, the JCPDS and the literature do not contain enough data on the Al-rich phases CrAl7 and Cr2Al11, and the determination of these data was a secondary aim of this work.To define a matrix of Cr-Al diffusion couples, Cr-Al films were deposited with two sets of variables: Al or Al-Si, and broken vacuum or single pumpdown. All films were deposited on 2-1/4-inch thermally oxidized Si substrates. A 500-Å layer of Cr was deposited at 120 Å/min on substrates at room temperature, in a vacuum system that had been pumped to 2 x 10-6 Torr. Then, with or without vacuum break, a 1000-Å layer of Al or Al-Si was deposited at 35 Å/s, with the substrates still at room temperature.

Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

1990 ◽  
Vol 48 (4) ◽  
pp. 172-173
Author(s):  
Naoki Yamamoto ◽  
Makoto Kikuchi ◽  
Tooru Atake ◽  
Akihiro Hamano ◽  
Yasutoshi Saito
Keyword(s):  
Phase Transition ◽  
Electron Microscope Study ◽  
Room Temperature ◽  
Hexagonal Lattice ◽  
Ferroelectric Materials ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Periodic Arrays ◽  
Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

STEM and ELS Observation of Early Oxide Formation on the Surface of Cr Thin Films

1980 ◽  
Vol 38 ◽  
pp. 412-413
Author(s):  
Fumio Watari ◽  
J. M. Cowley
Keyword(s):  
Thin Films ◽  
Optical System ◽  
Room Temperature ◽  
Oxide Formation ◽  
Initial Nucleation ◽  
Diffraction Patterns ◽  
Relationship Of ◽  
Multiple Twinning ◽  
Moderately High Temperature

STEM coupled with the optical system was used for the investigation of the early oxidation on the surface of Cr. Cr thin films (30 – 1000Å) were prepared by evaporation onto the polished or air-cleaved NaCl substrates at room temperature and 45°C in a vacuum of 10−6 Torr with an evaporation speed 0.3Å/sec. Rather thick specimens (200 – 1000Å) with various preferred orientations were used for the investigation of the oxidation at moderately high temperature (600 − 1100°C). Selected area diffraction patterns in these specimens are usually very much complicated by the existence of the different kinds of oxides and their multiple twinning. The determination of the epitaxial orientation relationship of the oxides formed on the Cr surface was made possible by intensive use of the optical system and microdiffraction techniques. Prior to the formation of the known rhombohedral Cr2O3, a thin spinel oxide, probably analogous to γ -Al203 or γ -Fe203, was formed. Fig. 1a shows the distinct epitaxial growth of the spinel (001) as well as the rhombohedral (125) on the well-oriented Cr(001) surface. In the case of the Cr specimen with the (001) preferred orientation (Fig. 1b), the rings explainable by spinel structure appeared as well as the well defined epitaxial spots of the spinel (001). The microdif fraction from 20A areas (Fig. 2a) clearly shows the same pattern as Fig. Ia with the weaker oxide spots among the more intense Cr spots, indicating that the thickness of the oxide is much less than that of Cr. The rhombohedral Cr2O3 was nucleated preferably at the Cr(011) sites provided by the polycrystalline nature of the present specimens with the relation Cr2O3 (001)//Cr(011), and by further oxidation it grew into full coverage of the rest of the Cr surface with the orientation determined by the initial nucleation.

Survival of mouse blastocysts after low-temperature preservation under high pressure

2004 ◽  
Vol 52 (4) ◽  
pp. 479-487 ◽  
Author(s):  
Cs. Pribenszky ◽  
M. Molnár ◽  
S. Cseh ◽  
L. Solti
Keyword(s):  
Phase Transition ◽  
Hydrostatic Pressure ◽  
Low Temperature ◽  
High Hydrostatic Pressure ◽  
Room Temperature ◽  
Freezing Point ◽  
Significant Loss ◽  
Embryo Cryopreservation ◽  
Subzero Temperatures ◽  
Survival Capacity

Cryoinjuries are almost inevitable during the freezing of embryos. The present study examines the possibility of using high hydrostatic pressure to reduce substantially the freezing point of the embryo-holding solution, in order to preserve embryos at subzero temperatures, thus avoiding all the disadvantages of freezing. The pressure of 210 MPa lowers the phase transition temperature of water to -21°C. According to the results of this study, embryos can survive in high hydrostatic pressure environment at room temperature; the time embryos spend under pressure without significant loss in their survival could be lengthened by gradual decompression. Pressurisation at 0°C significantly reduced the survival capacity of the embryos; gradual decompression had no beneficial effect on survival at that stage. Based on the findings, the use of the phenomena is not applicable in this form, since pressure and low temperature together proved to be lethal to the embryos in these experiments. The application of hydrostatic pressure in embryo cryopreservation requires more detailed research, although the experience gained in this study can be applied usefully in different circumstances.

A New Method for Direct Determination of the Recoilless Fraction with Application to Magnetic Nanoparticles

2002 ◽  
Vol 721 ◽  
Author(s):  
Monica Sorescu
Keyword(s):  
Room Temperature ◽  
Average Particle Size ◽  
Direct Determination ◽  
Average Particle ◽  
Lattice Method ◽  
Recoilless Fraction ◽  
Single Room ◽  
Magnetite Particles ◽  
Physical Mixtures

AbstractWe propose a two-lattice method for direct determination of the recoilless fraction using a single room-temperature transmission Mössbauer measurement. The method is first demonstrated for the case of iron and metallic glass two-foil system and is next generalized for the case of physical mixtures of two powders. We further apply this method to determine the recoilless fraction of hematite and magnetite particles. Finally, we provide direct measurement of the recoilless fraction in nanohematite and nanomagnetite with an average particle size of 19 nm.

Single Crystal Growth of High-Pressure Phases of Ice and Salt Hydrate Far Below the Original Melting Point by Mixing Alcohol: Crystal Structure Determination of Magnesium Chloride Heptahydrate

2020 ◽  
Author(s):  
Keishiro Yamashita ◽  
Kazuki Komatsu ◽  
Hiroyuki Kagi
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Crystal Growth ◽  
Single Crystal ◽  
Room Temperature ◽  
Growth Technique ◽  
Salt Hydrate ◽  
X Ray

An crystal-growth technique for single crystal x-ray structure analysis of high-pressure forms of hydrogen-bonded crystals is proposed. We used alcohol mixture (methanol: ethanol = 4:1 in volumetric ratio), which is a widely used pressure transmitting medium, inhibiting the nucleation and growth of unwanted crystals. In this paper, two kinds of single crystals which have not been obtained using a conventional experimental technique were obtained using this technique: ice VI at 1.99 GPa and MgCl<sub>2</sub>·7H<sub>2</sub>O at 2.50 GPa at room temperature. Here we first report the crystal structure of MgCl2·7H2O. This technique simultaneously meets the requirement of hydrostaticity for high-pressure experiments and has feasibility for further in-situ measurements.

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