Phase Transition and Formation of TiSi2 Codeposited on Atomically Clean Si(111).

1993 ◽  
Vol 311 ◽  
Author(s):  
Hyeongtag Jeon ◽  
Y. S. Cho ◽  
E. Y. Kang ◽  
J. W. Park ◽  
R.R. Nemanich
Keyword(s):  
Phase Transition ◽  
Phase Transformation ◽  
High Temperature ◽  
Rough Surface ◽  
Smooth Surface ◽  
Elevated Temperatures ◽  
Titanium Silicide ◽  
Surface And Interface ◽  
Si Substrates ◽  
Si Films

ABSTRACTIn this study, the phase transformation and the surface and interface morphologies of TiSi2 formed on atomically clean Si substrates are investigated. 200Å Ti and 400A Si films on Si(111) have been co-deposited at elevated temperatures (400°C - 800°C) in ultrahigh vacuum. The phase transition of TiSi2 is characterized with using XRD. The results distinguish the formation of the C49 and C54 crystalline titanium silicides. The surface and interface morphologies of titanium silicides have been examined with SEM and TEM. A relatively smooth surface is observed for the C49 phase while a rough surface and interface are observed for the C54 phase. The islanding of the C54 phase becomes severe at high temperature (800°C). Islands of TiSi2 have been observed at temperatures above 700°C but no islands are observed at temperatures below 600°C. For films deposited at 400TC and 500°C, weak XRD peaks corresponding to TiSi were observed and TEM micrographs exhibited small crystalline regions of titanium silicide at the interface.

Phase transformation and layer evolution in molybdenum disilicide-silicon carbide nanolayered coatings

1994 ◽  
Vol 52 ◽  
pp. 538-539
Author(s):  
H. Kung ◽  
T. R. Jervis ◽  
J.-P. Hirvonen ◽  
M. Nastasi ◽  
T. E. Mitchell ◽  
...  
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Oxidation Resistance ◽  
Elevated Temperatures ◽  
Matrix Material ◽  
Molybdenum Disilicide ◽  
High Temperature Strength ◽  
Cross Sectional ◽  
Good Oxidation Resistance ◽  
Structural Applications

MoSi2 is a potential matrix material for high temperature structural composites due to its high melting temperature and good oxidation resistance at elevated temperatures. The two major drawbacksfor structural applications are inadequate high temperature strength and poor low temperature ductility. The search for appropriate composite additions has been the focus of extensive investigations in recent years. The addition of SiC in a nanolayered configuration was shown to exhibit superior oxidation resistance and significant hardness increase through annealing at 500°C. One potential application of MoSi2- SiC multilayers is for high temperature coatings, where structural stability ofthe layering is of major concern. In this study, we have systematically investigated both the evolution of phases and the stability of layers by varying the heat treating conditions.Alternating layers of MoSi2 and SiC were synthesized by DC-magnetron and rf-diode sputtering respectively. Cross-sectional transmission electron microscopy (XTEM) was used to examine three distinct reactions in the specimens when exposed to different annealing conditions: crystallization and phase transformation of MoSi2, crystallization of SiC, and spheroidization of the layer structures.

Mn-Mg disordering in cummingtonite: a high-temperature neutron powder diffraction study

2000 ◽  
Vol 64 (2) ◽  
pp. 255-266 ◽  
Author(s):  
J. J. Reece ◽  
S. A. T. Redfern ◽  
M. D. Welch ◽  
C. M. B. Henderson
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
New York ◽  
High Temperature ◽  
Powder Diffraction ◽  
Elevated Temperatures ◽  
Neutron Powder Diffraction ◽  
Site Preference ◽  
A Site

AbstractThe crystal structure of a manganoan cummingtonite, composition [M4](Na0.13Ca0.41Mg0.46Mn1.00) [M1,2,3](Mg4.87Mn0.13)(Si8O22)(OH)2, (Z = 2), a = 9.5539(2) Å, b = 18.0293(3) Å, c = 5.2999(1) Å, β = 102.614(2)° from Talcville, New York, has been refined at high temperature using in situ neutron powder diffraction. The P21/m to C2/m phase transition, observed as spontaneous strains +ε1 = −ε2, occurs at ˜107°C. Long-range disordering between Mg2+ and Mn2+ on the M(4) and M(2) sites occurs above 550°C. Mn2+ occupies the M(4) and M(2) sites preferring M(4) with a site-preference energy of 24.6±1.5 kJ mol−1. Disordering induces an increase in XMnM2 and decrease in XMnM4 at elevated temperatures. Upon cooling, the ordered states of cation occupancy are ‘frozen in’ and strains in lattice parameters are maintained, suggesting that re-equilibration during cooling has not taken place.

Phenomena And Mechanism On Phase Transformation Twinning In Nanocrystalline BaTiO3

2010 ◽  
Vol 1256 ◽  
Author(s):  
Sujata Mazumder ◽  
Jiten Ghosh
Keyword(s):  
Phase Transition ◽  
Phase Transformation ◽  
High Temperature ◽  
Intermediate Phase ◽  
High Vacuum ◽  
Point Group ◽  
Atomic Scale ◽  
Twin Structure ◽  
High Temperature Xrd ◽  
Low Symmetry

AbstractThe detailed structure of nanocrystalline BaTiO3 powder during ball milling has been studied using XRD & TEM. The study illustrates important advances in understanding atomic scale properties of this material. Ferroelectric BaTiO3 powder undergoes phase transformation along the sequence Cubic(Pm3m)-tetragonal(P4mm)-orthohombic (Amm2)-rhombohedral(R3m) structure when pressureless sintered samples are cooled from high temperature to low temperature. The high to low symmetry phases are not related to group subgroup symmetry as transformation is discontinuous and first order in nature and the twin relationship in the low symmetry is forbidden by Landau theory. In case of ball milled BaTiO3 powder a continuous and diffusionless phase transition occur via second order to and from a metastable intermediate phase. In this pathway crystallites in the aggregation are twinned and the twin structure is related to crystal point group m3m which in the present case is illustrated as having 6mm symmetry formed under low driving force. The unit cell evolution due to phase transition and the crystallographic relationship are established. The phase transformation, coalescence and twin structure of thermally annealed BaTiO3 nanocrystals under high vacuum has been investigated using in situ high temperature XRD. The structure analysis is performed with the use of the method of computer modelling of disorder structure and simulation of corresponding diffraction pattern.

Enhanced Performance Induced by Phase Transition of Li2FeSiO4 upon Cycling at High Temperature

2020 ◽  
Author(s):  
Titus Masese ◽  
Yuki Orikasa ◽  
Kentaro Yamamoto ◽  
Yosuke Horie ◽  
Rika Hagiwara ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transformation ◽  
High Temperature ◽  
High Temperatures ◽  
Room Temperature ◽  
High Energy ◽  
Temperature Cycling ◽  
High Energy Density ◽  
Slow Phase ◽  
Rate Performance

<p>Owing to its low cost, thermal stability and theoretically high capacity, Li<sub>2</sub>FeSiO<sub>4 </sub>has been a promising cathode material for high-energy-density Li-ion (Li<sup>+</sup>) battery system. However, its poor rate performance and high voltage polarisation attributed to innately slow Li<sup>+</sup> kinetics at room temperature, has fundamentally curbed its ascent into prominence. Here, the rate performance of Li<sub>2</sub>FeSiO<sub>4</sub> at high temperatures in electrolyte comprising molten salt (ionic liquid) was investigated. Subsequently, a comparison of the phase transition behaviour observed at both high-temperature and room-temperature cycling was elucidated. Our results show that remarkable rate performance with good cyclability in conjunction with low voltage polarisation is attained upon cycling of Li<sub>2</sub>FeSiO<sub>4</sub> at high temperatures, due to the faster phase transformation from unstable monoclinic structures to thermodynamically stable orthorhombic structures triggered by elevated temperature. What this study adds to the burgeoning body of research work relating to the silicates is that the initially slow phase transformation behaviour observed at room temperature can significantly be enhanced upon cycling at elevated temperatures.</p>

Phase transition regulation and piezoelectric performance optimization of fresnoite crystal for high temperature acceleration sensing

2021 ◽  
Author(s):  
Chao Jiang ◽  
Caizi Zhang ◽  
Fangfei Li ◽  
Li Sun ◽  
Yanlu Li ◽  
...  
Keyword(s):  
Phase Transition ◽  
Electrical Resistivity ◽  
High Temperature ◽  
Performance Optimization ◽  
Elevated Temperatures ◽  
Piezoelectric Response ◽  
Potential Candidate ◽  
High Electrical Resistivity ◽  
Sensing Applications ◽  
Piezoelectric Performance

Fresnoite crystal, Ba2TiSi2O8 (BTS), is a potential candidate for high temperature piezoelectric sensing applications, due to high electrical resistivity and strong piezoelectric response at elevated temperatures. However, anomalies of electro-elastic...

Study on the Phase Transition from Amorphous Phases to Crystalline TiSi2

1995 ◽  
Vol 402 ◽  
Author(s):  
H. G. Nam ◽  
Nam-Ihn Cho
Keyword(s):  
Phase Transition ◽  
Distribution Functions ◽  
Titanium Silicide ◽  
Atomic Ordering ◽  
Amorphous Phases ◽  
Si Substrates ◽  
Transmission Electron ◽  
Short Range Ordering ◽  
Silicide Compounds ◽  
Deposition Conditions

AbstractTitanium silicides were prepared by coevaporation of Ti and Si on Si substrates at intermediate substrate temperatures followed by high temperature annealing. Depending on the deposition conditions, transmission electron diffraction analyses revealed two different halo patterns from the as-deposited samples. Variations in the deposition conditions included substrate temperature, deposition rate, and film thickness. Radial distribution functions were calculated to estimate the short range ordering of the amorphous phases. The interatomic distances of all the titanium silicide compounds were also calculated in order to compare them with the atomic ordering of amorphous phases. Phase transition from these amorphous phases to the first crystalline silicide is discussed in terms of kinetic variations as well as the atomic ordering.

Tension - Compression Asymmetry in Co49Ni21Ga30 High-Temperature Shape Memory Alloy Single Crystals

2013 ◽  
Vol 738-739 ◽  
pp. 82-86 ◽  
Author(s):  
Thomas Niendorf ◽  
Jayaram Dadda ◽  
Jan Lackmann ◽  
James A. Monroe ◽  
Ibrahim Karaman ◽  
...  
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Stress State ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Single Crystals ◽  
Stress Level ◽  
Elevated Temperatures ◽  
Stress States ◽  
Tension Compression Asymmetry

This paper reports on the tension-compression asymmetry of [001]-oriented Co49Ni21Ga30 single crystals at elevated temperatures. Maximum strains of -4.8 % and 8.6 % in compression and tension, respectively, were found. A linear Clausius-Clapeyron relationship was observed for both stress-states where the smaller slope in tension resulted in a significant increase of the phase transformation temperatures with stress, which reached 180 °C under a constant stress level of 150 MPa. In addition, the material demonstrated a large pseudoelastic temperature range of about 300 °C under both stress state conditions. The results in this study unequivocally indicate the potential of these alloys for applications where elevated temperatures and stress levels prevail.

Suppression of the Phase Transition and Agglomeration of TiSi2 by Addition of Zr Element

1998 ◽  
Vol 514 ◽  
Author(s):  
Sanghyun Yoon ◽  
Hyeongtag Jeon
Keyword(s):  
Phase Transition ◽  
High Temperatures ◽  
Lower Surface ◽  
Ex Situ ◽  
Vacuum Furnace ◽  
Ion Pump ◽  
Cross Sectional ◽  
Surface And Interface ◽  
Si Substrates

ABSTRACTThe formation of C49 TiSi2 phase at high temperatures was investigated by adding the Zr contents in Ti-silicide film. Stabilizing the C49 TiSi2 phase which exhibits lower surface and interface energies than those of the C54 TiSi2 phase at high temperatures was expected to suppress the problems of Tisilicide, such as the phase transition and the film agglomeration. The thin films of Ti and Zr were codeposited (40 nm) on Si substrates in the dual e-beam evaporation system equipped with an ion pump and its base pressure of ∼5 × 10−9 torr. The amounts of Zr contents (5 and 10 atomic %) added on Tisilicide were monitored by in-situ quartz crystal monitor. Immediately after the deposition, this film was annealed by ex-situ vacuum furnace at temperatures between 600 °C and 900 °C in 100 °C increments. The identification of the phase and the chemical composition were investigated by XRD and AES, respectively. The surface and interface morphologies were examined using cross-sectional TEM. The phase transition temperature of TiSi2 was raised with increasing Zr contents. The agglomeration of TiSi2 film was also suppressed by adding Zr element and much improved interface morphologies were observed.

TiSi2 Phase Transformation by Amorphization Techniques

1996 ◽  
Vol 441 ◽  
Author(s):  
Tord Karlin ◽  
Martin Samuelsson ◽  
Stefan Nygren ◽  
Mikael östling
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Low Temperature ◽  
Ion Beam ◽  
High Energy ◽  
Titanium Silicide ◽  
Silicide Phase ◽  
Rapid Thermal Anneal ◽  
Ion Beam Mixing ◽  
Line Widths

AbstractULSI packing density calls for sub-micron line widths, but on n-type polysilicon this can lead to incomplete titanium silicide C49 to C54 phase transformation after a conventional two step rapid thermal anneal (RTA). This study compares three different ion beam amorphization techniques: preamorphization, ion beam mixing and silicide amorphization, aiming at a complete phase transformation for submicron silicide lines. For preamorphization, an arsenic implantation at moderate energies (35–75 keV) was used to amorphize the top layer of the polysilicon prior to the titanium deposition. Ion beam mixing used a high-energy (200 keV) arsenic implantation after the titanium deposition to create an amorphous mix of silicon and titanium. These two methods did, each by themselves, lead to an increased fraction of C54 silicide grains already during the low temperature RTA, and a complete phase transformation during the subsequent high temperature RTA. Both methods lowered the thickness difference between titanium silicide on p- and n-type silicon. Silicide amorphization with 75 keV arsenic or 100 keV antimony, applied before the second RTA, did not significantly improve the silicide phase transformation.

Effect of (La0.5Sr0.5)CoO3 and Pt intermediate layers on improving the stability of Pb1–xLaxTi1–x/4O3 films

1998 ◽  
Vol 13 (5) ◽  
pp. 1286-1290 ◽  
Author(s):  
J. P. Wang ◽  
Y. C. Ling ◽  
Y. K. Tseng ◽  
K. S. Liu ◽  
I. N. Lin
Keyword(s):  
High Temperature ◽  
Perovskite Phase ◽  
Grazing Angle ◽  
Silicon Substrates ◽  
Significant Deterioration ◽  
Si Substrates ◽  
Intermediate Layers ◽  
Platinum Coating ◽  
The Stability ◽  
Si Films

Deposition of a (La0.5Sr0.5)CoO3 (LSCO) layer on top of Pt/Ti/Si substrates was observed to substantially improve the stability of the subsequently deposited Pb1−xLaxTi1−x/4O3 (PLT) films. Platinum coating of silicon substrates by itself is known to enhance the formation of PLT phase. In this paper, the elemental depth profile examined by secondary ion mass spectroscopy (SIMS) and the structural profile examined by grazing angle incident x-ray diffractometry (GIXD) reveals that the Ti species precoated underneath the Pt layer diffuses outward through the Pt layer at high temperature, forming a rutile TiO2 layer on top of Pt coating. It is this outermost TiO2 layer which promotes the transformation kinetics of the PLT species adhered onto substrates into the perovskite phase. Thus obtained films (PLT/Pt/Ti/Si) are, however, not stable enough to survive subsequent high-temperature processing. On the other hand, the PLT/LSCO/Pt/Ti/Si films, which incorporate LSCO as buffer layer, can survive 650 °C without significant deterioration.

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