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VDOS calculations for MgGeO3 have been determined by integrating phonon dispersions which were handled with DFPT where the "Brillouin-zone sampling for phonon states was computed on 14, 18, and 14 q-points" for all phases. Force constant matrices on the finer q-point grids were interpolated by applying the acoustic sum rule as indicated by Tsuchiya et al.

Re: VDOS by GREGORY WROBELGREGORY WROBEL, 04 May 2010 21:02

Wilson et al have stated there is no experimental structural data for FeTiO3 to data. Liu et al have not calculated bulk moduli in their calculations. Tsuchiya et al. have given theoretical MgGeO3 bulk moduli values of ilmenite, perovskite and postperovskite as 179.2GPa, 322.8GPa and 433.0GPa respectively. Experimentally it's been found that MgGeO3 bulk moduli values of ilmenite, perovskite and postperovskite are 187 +/-2GPa, 229 +/-3GPa and 210 +/-20GPa. This indicates discrepancy between experimental their and theoretical data.

by GREGORY WROBELGREGORY WROBEL, 04 May 2010 20:54

Hi Greg,

Thanks for your suggestions. I tried to provide more information on how the experiment were performed. However I can not answer the question about the computational part exactly.

by YASEMIN KUTESYASEMIN KUTES, 04 May 2010 20:47

Hi Ying,

Thank you for your suggestion. I will add it in my term paper. To answer your question,the experiment of polyethylene dielectric constant is around 2,so DFPT has a relatively good agreement with experiment value.For MD,since it only calculate the ionic and dipolar contributions to dielectric constant, for nonpolar system,sometimes it may underestimate the dielectric constant.As for ice,I didn't find the experiment value……

by CHENCHEN WANGCHENCHEN WANG, 04 May 2010 20:32

Ilmenites are considered as ceramics. They can be synthesized from a variety of techniques such as hydrothermal synthesis, solid-state reaction at high temperature and pressure, CVD, and sol-gel techniques just to name a few.

by GREGORY WROBELGREGORY WROBEL, 04 May 2010 20:09

Ideally, dopants that lower the effective band gap of ZnSnO3 (with lithium niobate crystal structure) are desired. For photovoltaic application, its desirable to have a band gap of ~1.2eV which will utilize photon energies from infrared through UV. If LN-type ZnSnO3 has a band gap much larger than the predicted 1eV, dopants can be used to lower the effective band gap to the desired ~1.2eV. Attention will be focused on elements with high valency and size comparable to the intrinsic vacancies to minimize lattice distortions.

It's been shown in various aritcles that Fe, Cu, Mn, Ce Mg, Zn, In, Sc and Hf have been used to alter photorefraction properties of lithium niobate. Therefore dopants can be used to alter band gap within these types of structures.

by GREGORY WROBELGREGORY WROBEL, 04 May 2010 19:59

Yes BMG have been studied for biomedical applications particularly in terms of biodegradable implant devices. The major motivation for implants that self-destruct after a set duration is that there is no need for a second surgery to remove the implant after the natural biological structure has been repaired. Mg-based BMG's have been used from their processing as fine amorphous wires. BMG's show promise in the sense that they have great viscous flow during processing such that they show near-net-shape casting ability.

by Kyle CrosbyKyle Crosby, 04 May 2010 19:42

There is certainly a porosity dependence, the overall bulk modulus is a function of the titanium bulk modulus over the matrix bulk modulus ratio, which is an inverse function of the porosity and pore stiffness. Typically as the pore size increases and the overall fraction of porosity increases, the mechanical strength of the material decreases thus the bulk modulus of the component shows a decrease.

The bulk modulus can be adjusted by process the materials with a textured grain structure, i.e. single crystals have one texture throughout the component while polycrystalline materials have a more or less random texture. So if you can process your material with a harder crystallographic direction along the loading axis, you should end up with a higher elastic modulus or the opposite for materials processed with particular soft direction in mind. Also the use of a composite structure would be a suitable method for adjusting the bulk modulus while keeping the chemistry constant.

by Kyle CrosbyKyle Crosby, 04 May 2010 19:35

The DFT study of the lithium niobate phase of ZnSnO3 has no experimental data to compare to. The high pressure/temperature literature made no predictions of the band gap or electronic structure. So far, bad gap comparisons for materials related to ZnSnO3, by the fact that they're main group oxides possessing edge-sharing octahedra, have shown theoretical bang gaps are on average 0.7-1.5eV lower than experiment.

by GREGORY WROBELGREGORY WROBEL, 04 May 2010 19:23

Yes, the domain walls can take on different orientations. PZT can have 45, 90 and 180 degree domains, depending on factors such as the composition, strain in the system and crystal structure orientation.

by Vincent PalumboVincent Palumbo, 04 May 2010 19:20

As to the growth rate…there are a few factors to consider, age and status of the health of the bone. Pre-natally bone growth is the most rapid (2-4 inches per year), it slows during childhood (1-2 inches per year), and stops altogether after puberty as an adult. Also when a bone is broken or damaged the rate of growth is substantially faster than during normal unperturbed growth, however rapid bone growth is often defined by random orientation and as a weak non-lamellar structure. Slow bone growth is stronger mechanically because the osteoblasts provide a well define longitudinal geometry. You can click here to see typical bone growth trend.

http://www.imagingeconomics.com/library/200203-10/40-1.jpg

In terms of the inert surface coating, yes that has been utilized by applying hydroxyapatite coatings which are bioactive but do not show significant Al or V diffusion through its thickness. Currently Ti 6-4 is still the load bearing alloy of choice for implant devices.

by Kyle CrosbyKyle Crosby, 04 May 2010 19:19

Hi, Chenchen,
  What is the accuracy of your results? I think it would be better if you also list the experiment result in your table,

by YING SUNYING SUN, 04 May 2010 18:58

Hi, vincent
I have not done any real calculation on how the byproduct of cable cure treatment effect the electronic structures of PE. Carbonyl and vinyl impurities are simple molecular usually found in PE cable during the manufacture procedure. People have calculated the results of carbonyl and vinyl, and I will use it as a guide how I will analyze the calculation results, what I could do..etc. I think the chemical reaction of water tree cure is very complex, mainly including polymerization.

by YING SUNYING SUN, 04 May 2010 18:47

In Cable cure treatments, the fluid diffuses from the strands into the insulation, where it polymerizes with the water in the micro voids and fills them with a dielectric fluid. The reaction take place is very complex. But it will be a good idea to introduce the background of water treeing more explicitly.

I see that you mention the computations are very time intensive….can you just elaborate on the order of magnitude difference in computation time between crystalline materials versus modeling of amorphous materials.

by Kyle CrosbyKyle Crosby, 04 May 2010 18:39

Hey Vin,

I'm not real up to date with my magnetic properties, but are there any other domain wall configurations that these materials can adopt, i.e. I see you describe 180 degree domains, are there cases where other geometries form?

by Kyle CrosbyKyle Crosby, 04 May 2010 18:37

I agree with you, especially the working temperature of PE cable is high, about 90 degree C.

Re: Temperature cosideration by YING SUNYING SUN, 04 May 2010 18:34

Hi,Yang,
yes, I think a single polymer chain is considered as a lattice point when calculating lattice parameters of PE. DFT model of polymer is difficult if take the chain conformation and movement into account. In previous DFT approach, most of the calculations are done in crystalline PE which has a orthorhombic structure. Core-shell model give the system freedom to distort just like the chain conformation. Maybe future work could be considering how the set a polymer model more realistic to the actual situation.

Re: unit cell for polymer by YING SUNYING SUN, 04 May 2010 18:31

Impurities in the bulk are handled using the supercell approach, in which the impurity is placed in an enlarged bulk unit cell, so that the impurity does not interact
appreciably with its periodic image. In the my lab mate’s previous present work, an enlarged
192-atom unit cell (or supercell) consisting of eight PE chains, each having eight ethylene groups, was employed to model crystalline PE with an impurity .In addition
to the 192-atom supercell which is constrained by the outer orthorhombic boundaries, a second supercell was employed in which the PE chains have considerably more freedom to relax.
This structure consists of a “Core” chain, to which the chemical impurity is added, surrounded by six“Shell” chains. The seven chains are in a supercell large enough to prevent interaction with chains in neighboring replicas. Each of the seven chains consists of 40 carbon atoms and is terminated by a methyl group (C40H82).

Re: core-shell model by YING SUNYING SUN, 04 May 2010 18:23

Hi Yasemin,

So far I have a couple suggestions:

1) In the experimental section, I don't think it's clear how they actually performed the experiment to measure the band gap. Can you please specify and/or elaborate on that?
2) In the computational section, I think it would be interesting to know how they modeled the system in the supercell: just a single layer with how many atoms?

by Gregory Santone JrGregory Santone Jr, 04 May 2010 17:45
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