Total Energy Differences Between Silicon Carbide Polytypes and their Implications for Crystal Growth

1997 ◽  
Vol 492 ◽  
Author(s):  
Sukit Llmpijumnong ◽  
Walter R. L. Lambrecht
Keyword(s):  
Silicon Carbide ◽  
Crystal Growth ◽  
Epitaxial Growth ◽  
Size Effects ◽  
Nearest Neighbor ◽  
Orbital Method ◽  
Full Potential ◽  
Neighbor Interaction ◽  
Island Size ◽  
Annni Model

ABSTRACTThe energy differences between various SiC polytypes are calculated using the full-potential linear muffin-tin orbital method and analyzed in terms of the anisotropie next nearest neighbor interaction (ANNNI) model. The fact that J1 + 2J2 < 0 with J1 > 0 implies that twin boundaries in otherwise cubic material are favorable unless twins occur as nearest neighbor layers. Contrary to some other recent calculations we find J1 > |J2|. We discuss the consequences of this for stabilization of cubic SiC in epitaxial growth, including considerations of the island size effects.

Silicon Carbide: Progress in Crystal Growth

1987 ◽  
Vol 97 ◽  
Author(s):  
J. Anthony Powell
Keyword(s):  
Silicon Carbide ◽  
Crystal Growth ◽  
High Temperature ◽  
Epitaxial Growth ◽  
Recent Progress ◽  
Single Crystal Silicon ◽  
Silicon Substrates ◽  
Large Area ◽  
High Quality ◽  
Crystal Silicon

ABSTRACTSilicon carbide (SiC), with a favorable combination of semiconducting and refractory properties, has long been a candidate for high temperature semiconductor applications. Research on processes for producing the needed large-area high quality single crystals has proceeded sporadically for many years. Two characteristics of SiC have aggravated the problem of its crystal growth. First, it cannot be melted at any reasonable pressure, and second, it forms many different crystalline structures, called polytypes. Recent progress in the development of two crystal growth processes will be described. These processes are the modified Lely process for the growth of the alpha polytypes (e.g. 6H SiC), and a process for the epitaxial growth of the beta polytype (i.e. 3C or cubic SiC) on single crystal silicon substrates. A discussion of the semiconducting qualities of crystals grown by various techniques will also be included.

Electronic Structure and Magnetic Properties of Transition Metal Doped Silicon Carbide in Different Polytypes

2006 ◽  
Vol 527-529 ◽  
pp. 641-646 ◽  
Author(s):  
M.S. Miao ◽  
Walter R.L. Lambrecht
Keyword(s):  
Silicon Carbide ◽  
Transition Metal ◽  
Exchange Interaction ◽  
Density Functional ◽  
Magnetic Interactions ◽  
Orbital Method ◽  
Full Potential ◽  
Local Exchange ◽  
Doped Silicon ◽  
Metal Doped

We report density functional calculations using the full-potential linearized muffin-tin orbital method on early first row transition metal doped Silicon Carbide in both cubic (3C) and hexagonal (4H) polytypes. The energy levels in the gap for Ti, V and Cr are in good agreement with the available photoluminescence experiments. Our calculation shows that the Ti impurity is active for 4H but not for 3C, while V and Cr impurities are active for both polytypes. The magnetic interactions are very different for Cr and Mn. Cr shows a very local exchange interaction that decays rapidly, which is similar for different polytypes and different sites. The exchange interaction for Mn is quite long range and is very sensitive to the location of the Mn pairs.

Preparation, Electronic Structure and Optical Properties of the Electrochromic Thin Films

2004 ◽  
Vol 9 (4) ◽  
pp. 363-372 ◽  
Author(s):  
T. Lukaszewicz ◽  
A. Ravinski ◽  
I. Makoed
Keyword(s):  
Electrochromic Device ◽  
Orbital Method ◽  
Optical Parameters ◽  
Full Potential ◽  
Electrochromic Devices ◽  
Energy Bands ◽  
Conducting Film ◽  
Recombination Probability ◽  
Transparent Conducting ◽  
Smoluchowski Equations

A new multilayer electrochromic device has been constructed according to the following pattern: glass1/ITO/WO3/gel electrolyte/BP/ITO/glass2, where ITO is a transparent conducting film made of indium and tin oxide and with the surface resistance equal 8–10 Ω/cm2 . The electrochromic devices obtained in the research are characterized by great (considerable) transmittance variation between coloration and bleaching state (25–40% at applied voltage of 1.5 to 3 V), and also high coloration efficiency (above 100 cm2 /C). Selfconsistent energy bands, dielectric permittivity and optical parameters are calculated using a full-potential linear muffin-tin orbital method. The numerical solution of the Debye-Smoluchowski equations is developed for simulating recombination probability of Li+ ions in amorphous electrolyte.

ELASTIC PROPERTIES OF STRAINED FCC AND HCP IRON

1993 ◽  
Vol 07 (01n03) ◽  
pp. 207-211
Author(s):  
T. KRAFT ◽  
M. METHFESSEL ◽  
M. VAN SCHILFGAARDE ◽  
M. SCHEFFLER
Keyword(s):  
Energy Cost ◽  
Interplanar Distance ◽  
Orbital Method ◽  
Full Potential ◽  
Local Spin Density Approximation ◽  
Nearest Neighbour ◽  
Density Approximation ◽  
Neighbour Distance ◽  
Large Lattice ◽  
Fcc Phase

Using the full-potential linear muffin-tin orbital method within the local spin-density approximation we analyse the influence of the nearest neighbour distance on fcc(111) or hcp(0001) iron layers. The LDA-LSDA error in describing ferromagnetic phases is determined to be at least 15 mRy/atom. As a consequence of this error, our calculations favour paramagnetic ground states. In this sense, the reported results have some model character. However, our analysis of the elastic energy cost under distortions should hold for transition metals in general. Allowing relaxations of the interplanar distance the fcc phase can become energetically favourable over the hcp phase at large lattice mismatches. The main reason for this behaviour is the enhanced stiffness of the hcp interplanar bonds due to the shortening of the axial c/a ratio.

FIRST-PRINCIPLES HIGH-PRESSURE ELASTIC AND THERMODYNAMIC PROPERTIES OF TANTALUM

2011 ◽  
Vol 25 (10) ◽  
pp. 1393-1407 ◽  
Author(s):  
JING-HE WU ◽  
XIAN-LIN ZHAO ◽  
YOU-LIN SONG ◽  
GUO-DONG WU
Keyword(s):  
Thermodynamic Properties ◽  
Elastic Constants ◽  
First Principles ◽  
Equations Of State ◽  
Debye Model ◽  
Thermal Expansivity ◽  
Orbital Method ◽  
Full Potential ◽  
Body Centered Cubic ◽  
Theoretical Results

The all-electron full-potential linearized muffin-tin orbital method, by means of quasi-harmonic Debye model, is applied to investigate the elastic constant and thermodynamic properties of body-centered-cubic tantalum (bcc Ta). The calculated elastic constants of bcc Ta at 0 K is consistent with the previous experimental and theoretical results. Our calculations give the correct trends for the pressure dependence of elastic constants. By using the convenient quasi-harmonic Debye model, we refined the thermal equations of state. The thermal expansivity and some other thermal properties agree well with the previous experimental and theoretical results.

Processing Techniques of a Silicon Carbide Heat Exchanger and its Capable Properties – A Review

2015 ◽  
Vol 787 ◽  
pp. 513-517 ◽  
Author(s):  
R. Pachaiyappan ◽  
R. Gopinath ◽  
S. Gopalakannan
Keyword(s):  
Silicon Carbide ◽  
Heat Exchanger ◽  
Gas Turbines ◽  
Cooling System ◽  
Composite Ceramic ◽  
Processing Technique ◽  
Full Potential ◽  
Absorption Chillers ◽  
Evaporative Cooling System ◽  
Processing Techniques

Silicon carbides is a composite ceramic material produced from inorganic non-metallic substances, formed from the molten mass which solidifies on cooling and simultaneously matured by the action of heat. It is used in various applications such as grinding wheels, filtration of gases and water, absorption, catalyst supports, concentrated solar powers, thermoelectric conversion etc. The modern usage of silicon carbide is fabricated as a heat exchanger for high temperature applications. Leaving behind steel and aluminium, silicon carbide has an excellent temperature withstanding capability of 1425°C. It is resistant to corrosion and chemical erosion. Modern fusion reactors, Stirling cycle based gas turbines, evaporators in evaporative cooling system for air condition and generator in LiBr/H2O absorption chillers for air conditioning those systems heat transfer rate can be improved by replacing a present heat exchanger with silicon carbide heat exchanger. This review presents a detailed discussion about processing technique of such a silicon carbide. Modern known processing techniques are partial sintering, direct foaming, replica, sacrificial template and bonding techniques. The full potential of these materials can be achieved when properties are directed over specified application. While eyeing over full potential it is highly dependent on processing techniques.

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