scholarly journals Study on the Stability of Trivalent Cations Doped Zirconia through Atomistic Modeling

2019 ◽  
Vol 22 (4) ◽  
pp. 129-135
Author(s):  
Akram La Kilo ◽  
Triwahyuni S. Umamah ◽  
Lukman A. R. Laliyo
Keyword(s):  
Geometry Optimization ◽  
Lattice Energy ◽  
Atomistic Modeling ◽  
Cell Parameters ◽  
Short Range Potential ◽  
Atomistic Modelling ◽  
Trivalent Cations ◽  
The Difference ◽  
The Stability ◽  
Good Agreement

The aim of this research was to study the stability of the structure of the ZrO2 doped with trivalent oxide Zr1-xMxO2-δ (M = La3+, Nd3+, Sm3+, Eu3+, Gd3+, Y3+, Er3+, Yb3+ and Lu3+ through atomistic modelling and bond valence sum method. Short range potential used in this study was Buckinghams’ potential. Result of geometry optimization at constant pressure shown both cell parameters of ZrO2 was in good agreement with experimental results because of the difference was only 0.11%. Increasing the concentration and the size of substituting dopant of ZrO2 makes the lattice energy of the doped structure was more positive so that the stability of the doped ZrO2 structure decreases. The decrease in the stability of ZrO2 doped with Y3+, Er3+, Yb3+ and Lu3+was smaller than ZrO2 doped with La3+, Nd3+, Sm3+, Eu3+ and Gd3+. BVS results shown that the structure of ZrO2 doped with La3+was not appropriate because it has different value of BVS was more than 0.1

Energetics and Structural Effects of Boron Additive to Intermetallic Compound: γ-Tial

1990 ◽  
Vol 213 ◽  
Author(s):  
P.K. Khowash ◽  
D.L. Price ◽  
B.R. Cooper
Keyword(s):  
Intermetallic Compound ◽  
Total Energy ◽  
Site Selection ◽  
Lattice Structure ◽  
Practical Importance ◽  
The Difference ◽  
The Stability ◽  
Experimental Values ◽  
And Behavior ◽  
Good Agreement

ABSTRACTImproving the low temperature ductility of the intermetallic compound γ - TiAl by alloying with small concentrations of an additive is of great practical importance. The difference in site selection energy of the additive plays an important role in the stability and behavior of the alloy. For boron in L10 TiAl, we have calculated the site selection energy using linearized combination of muffin-tin orbitals (LMTO) total energy calculations. For pure γ - TiAl, we found the equilibrium lattice structure by minimizing the total energy, and obtained good agreement with the experimental values. With the introduction of boron, a relaxation of the lattice around the boron additive is expected. For boron additives, we have calculated the forces on each atom leading to the minimization of the total energy as a function of the ionic positions in order to obtain the “true” stable structure of the alloy.

scholarly journals Bond valence constraints on the composition of 3d-elements bearing tourmalines

2014 ◽  
Vol 70 (a1) ◽  
pp. C1118-C1118
Author(s):  
Oleg Vereshchagin ◽  
Olga Frank-Kamenetskaya ◽  
Ira Rozhdestvenskaya
Keyword(s):  
Aluminum Content ◽  
Divalent Cations ◽  
Bond Valence ◽  
Trivalent Cation ◽  
Charge Balance ◽  
Bivalent Cations ◽  
3D Elements ◽  
Trivalent Cations ◽  
The Stability ◽  
Good Agreement

F.C. Hawthorne (2002) and F. Bosi (2011) showed that bond valence approach is to be applied to stability prediction of tourmaline structure with different chemical composition. Using this approach we considered bond valence constraints on occupation of Y, Z, V and W sites of Cu-, Ni-bearing tourmalines. From the standpoint of the bond valence approach, [3YW] unit is unstable if W site is fully occupied by O2-. The stability of [3YW] unit decreases along a row: 3 divalent cations → 2 divalent cations + 1 trivalent cation → 2 trivalent cation + 1 divalent cations → 3 trivalent cations if W site is fully occupied by OH- or F-. There is no limitation on 3d elements and aluminum content in [2ZYV] if V site is fully occupied by OH-. The [2ZYV] unit is unstable if V site is fully occupied by O2-. The data, obtained from calculation of bond valences are in a good agreement with results of single crystal structure refinements of synthetic Cu- (Ertl et al., 2013) and Ni-tourmalines: Cu-bearing olenite with a CuO content of 8.39 wt.% [a = 15.849(1), c =7.087(1) Å, R = 2.5%] and Ni-bearing olenite with a NiO content of 18.96 wt.% [a = 15.890(2), c = 7.1815(8), R = 3.1%]. In all cases W and V sites are predominantly occupied by OH- anions. The composition of [3YW] units are [(Cu1.80Al1.20)(OH)0.60F0.40] and [(Ni1.80Al1.20)(OH)1.00]. Breaking of charge balance with increasing of bivalent cations is maintained by increasing of portion of vacancies at X site and increasing of content of trivalent cations (Al, B) at T site.

scholarly journals Methodology for calculating rope drums for stability

2021 ◽  
pp. 83
Author(s):  
Nаtalya Fidrovska ◽  
Viktoria Nesterenko ◽  
Ruslan Karavan
Keyword(s):  
Critical Load ◽  
Stability Margin ◽  
External Pressure ◽  
Shell Shape ◽  
Metal Consumption ◽  
Safety And Reliability ◽  
The Difference ◽  
The Stability ◽  
Stability Issues ◽  
Good Agreement

. The problems of the stability of rope drums are quite urgent. The rope drum is in most cases a thin-walled shell, which, under the influence of external pressure from the rope, can lead to loss of stability. The stability issues of the drum shell, which is loaded with rope turns, are very important, because the safety and reliability of the rope hoist is directly related to them The studies carried out made it possible to obtain a new method for calculating the stability of cylindrical shells, which takes into account not only the length of the shell, but also the rigidity of the connection with the head. In addition, a calculation formula was obtained to determine the critical pressure of the oval shell, which gives a fairly good agreement with the experiments of American scientists. The work also considered the effect of the difference in wall thickness on the critical load of the drum. The studies carried out made it possible to conclude that the parameters of the rope drums make it possible to completely eliminate the need to install rings and stiffeners. Also as a result of research it was found that the shell of the crane drum under the influence of a radial load cannot lose stability. Studies have shown that in all cases the stability margin of the rope drum shell is greater than the strength margin. In this case, the load created by the rope wound on the drum is considered, with the ratios of the radius of the drum and the rope typical for crane construction. In addition, a coefficient was established that takes into account the elasticity of the shell-head joint. The studies carried out have shown that such initial deviations of the drum shell shape as ovality do not give a significant increase in the critical load. The results obtained are quite important, since they allow reducing the metal consumption of the rope drum shell and at the same time ensuring its reliable operation. A decrease in metal consumption is achieved by reducing the thickness of the shell and the absence of the need to install rings and stiffeners. This will lead to a decrease in metal consumption and energy consumption of the crane itself, and also simplifies the technology of manufacturing a rope drum.

scholarly journals Stability Study of Four Layer Aurivillius Oxide of AxBi4-xTi4O15 (A = Ca, Sr, Ba): Atomistic Simulation

2020 ◽  
Vol 3 (2) ◽  
pp. 157
Author(s):  
Akram La Kilo ◽  
La Alio ◽  
La Ode Aman ◽  
Jafar La Kilo
Keyword(s):  
Atomistic Simulation ◽  
Research Method ◽  
Constant Pressure ◽  
Geometry Optimization ◽  
Lattice Energy ◽  
Stability Study ◽  
Perovskite Layer ◽  
Buckingham Potential ◽  
Lattice Energies ◽  
The Stability

Aurivillius is bismuth layered structure ferroelectrics that can be applied as memory, sensor, and catalyst. This research aimed to study the stability of AxBi4-xTi4O15 Aurivillius (A = Ca, Sr, and Ba). Dopants (A) partially substitute Bi at the sites of Bi(1) and Bi(2) of the perovskite layer. This research method is an atomistic simulation using by the GULP code. Simulations were carried out by means of AxBi4-xTi4O15 geometry optimization at constant pressure, using the Buckingham potential. The results showed that the increase in the concentration of dopants substituting Bi accompanied by an increase in lattice energies. The most stable Aurivillius was CaxBi4-xTi4O15 (x = 16.3%) carried out by Bi substitution at Bi(2) site, with lattice energy, -1668.227 eV. Aurivillius stability decreases by increasing the size of the dopant. The maximum concentration number of A dopant substituting Bi was discussed.

Development of Simple SPD Tight-Binding Models for Transition Metals

1997 ◽  
Vol 491 ◽  
Author(s):  
O. Le Bacq ◽  
F. Willaime ◽  
A. Pasturel
Keyword(s):  
Transition Metals ◽  
Tight Binding ◽  
Pair Potential ◽  
Basis Set ◽  
Atomistic Simulations ◽  
Band Model ◽  
The Difference ◽  
The Stability ◽  
Stability Results ◽  
Good Agreement

ABSTRACTA simple spd tight-binding scheme for atomistic simulations in transition metals is developed using an orthogonal basis set in the two-center approximation. The purpose of the present approach is to cope with the limitations of the canonical d-band model for elements at the beginning or at the end of the transition metal series while keeping a reduced number of parameters, and simple decay-functions. The parameters for the hopping integrals are fitted to FP-LMTO calculations of the volume dependence of band energies and band structures for several selected structures. Constant values are taken for the on-site energies, and the Born-Mayer pair potential is used for the repulsive term. Two approaches are compared for the total energy: the band model and the bond model. First applications are presented in the case of zirconium, where the difference between these models on phase stability results is particularly drastic. The bond model reproduces the stability of the hep phase and displays a good agreement with experiments for the elastic constants.

Biomechanical investigations of the secondary stability of commercial short dental implants in porcine ribs

2014 ◽  
Vol 59 (6) ◽  
Author(s):  
Rebecca Wilhelm ◽  
Istabrak Hasan ◽  
Ludger Keilig ◽  
Friedhelm Heinemann ◽  
Helmut Stark ◽  
...  
Keyword(s):  
Dental Implants ◽  
Measurement System ◽  
Experimental Results ◽  
Short Implants ◽  
The Difference ◽  
The Stability ◽  
Secondary Stability ◽  
Good Agreement

AbstractThe use of short implants has increased widely within the last years. However, the stability of these implants has not yet been comprehensively investigated, in particular the difference in geometry and dimension of short implants. The aim of the present study was to investigate experimentally the difference of the secondary stability of different commercial short implants by measuring their displacements. Eleven implant geometries were investigated in this study. A total of 22 implants were inserted in porcine rib segments, two implants for each system. Implant displacements were measured using a self-developed biomechanical hexapod measurement system (HexMeS). The highest displacement was observed with Straumann BL NC 3.3×8.0 mm (266 μm), followed by Straumann Standard 4.1×6.0 mm (156 μm), while the lowest displacement of 61 μm was shown by Dentaurum type 1 implant (4.2×5.0 mm). No obvious difference of displacements was observed between hammered and screw-shaped implants with relevant dimensions. The experimental results were in good agreement with the numerical ones (19–42%) for Dentaurum implants. However, a difference of 70–80% was obtained for the Astra implant (4.0×6.0 mm) and Bicon implant (6.0×5.7 mm). The geometry of short implants directly affects their stability within the bone.

Kinematical and Dynamical CBED Pattern Models: Increasing the Accuracy of the Unit-Cell Parameter Measurements Based on CBED Patterns

1990 ◽  
Vol 48 (2) ◽  
pp. 540-541
Author(s):  
I.N. Yadhikov ◽  
S.K. Maksimov
Keyword(s):  
Reciprocal Lattice ◽  
Unit Cell ◽  
Reciprocal Lattice Vector ◽  
Unit Cell Parameters ◽  
Lattice Vector ◽  
Cell Parameters ◽  
Accuracy Of Measurements ◽  
The Difference ◽  
Image Position ◽  
Convergent Beam

Convergent beam electron diffraction (CBED) is widely used as a microanalysis tool. By the relative position of HOLZ-lines (Higher Order Laue Zone) in CBED-patterns one can determine the unit cell parameters with a high accuracy up to 0.1%. For this purpose, maps of HOLZ-lines are simulated with the help of a computer so that the best matching of maps with experimental CBED-pattern should be reached. In maps, HOLZ-lines are approximated, as a rule, by straight lines. The actual HOLZ-lines, however, are different from the straights. If we decrease accelerating voltage, the difference is increased and, thus, the accuracy of the unit cell parameters determination by the method becomes lower.To improve the accuracy of measurements it is necessary to give up the HOLZ-lines substitution by the straights. According to the kinematical theory a HOLZ-line is merely a fragment of ellipse arc described by the parametric equationwith arc corresponding to change of β parameter from -90° to +90°, wherevector, h - the distance between Laue zones, g - the value of the reciprocal lattice vector, g‖ - the value of the reciprocal lattice vector projection on zero Laue zone.

Use of a Lyophilized Reference Plasma to Compare Coagulation Test Procedures

1975 ◽  
Vol 34 (02) ◽  
pp. 426-444 ◽  
Author(s):  
J Kahan ◽  
I Nohén
Keyword(s):  
Oral Anticoagulant Therapy ◽  
Repeated Measurements ◽  
Test Procedures ◽  
Coagulation Activity ◽  
Close Relationship ◽  
Measured Activity ◽  
Test Materials ◽  
The Difference ◽  
The Stability ◽  
The One

SummaryIn 4 collaborative trials, involving a varying number of hospital laboratories in the Stockholm area, the coagulation activity of different test materials was estimated with the one-stage prothrombin tests routinely used in the laboratories, viz. Normotest, Simplastin-A and Thrombotest. The test materials included different batches of a lyophilized reference plasma, deep-frozen specimens of diluted and undiluted normal plasmas, and fresh and deep-frozen specimens from patients on long-term oral anticoagulant therapy.Although a close relationship was found between different methods, Simplastin-A gave consistently lower values than Normotest, the difference being proportional to the estimated activity. The discrepancy was of about the same magnitude on all the test materials, and was probably due to a divergence between the manufacturers’ procedures used to set “normal percentage activity”, as well as to a varying ratio of measured activity to plasma concentration. The extent of discrepancy may vary with the batch-to-batch variation of thromboplastin reagents.The close agreement between results obtained on different test materials suggests that the investigated reference plasma could be used to calibrate the examined thromboplastin reagents, and to compare the degree of hypocoagulability estimated by the examined PIVKA-insensitive thromboplastin reagents.The assigned coagulation activity of different batches of the reference plasma agreed closely with experimentally obtained values. The stability of supplied batches was satisfactory as judged from the reproducibility of repeated measurements. The variability of test procedures was approximately the same on different test materials.

Explaining the magnetism of gold

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Gas Phase ◽  
Computational Study ◽  
Formation Enthalpy ◽  
Gold Atom ◽  
Orbital Energy ◽  
Knudsen Effusion ◽  
Energy Diagram ◽  
Unpaired Electrons ◽  
The Difference ◽  
Good Agreement

<p>In the present work, a computational study is performed in order to clarify the possible magnetic nature of gold. For such purpose, gas phase Au<sub>2</sub> (zero charge) is modelled, in order to calculate its gas phase formation enthalpy. The calculated values were compared with the experimental value obtained by means of Knudsen effusion mass spectrometric studies [5]. Based on the obtained formation enthalpy values for Au<sub>2</sub>, the compound with two unpaired electrons is the most probable one. The calculated ionization energy of modelled Au<sub>2</sub> with two unpaired electrons is 8.94 eV and with zero unpaired electrons, 11.42 eV. The difference (11.42-8.94 = 2.48 eV = 239.29 kJmol<sup>-1</sup>), is in very good agreement with the experimental value of 226.2 ± 0.5 kJmol<sup>-1</sup> to the Au-Au bond<sup>7</sup>. So, as expected, in the specie with none unpaired electrons, the two 6s<sup>1</sup> (one of each gold atom) are paired, forming a chemical bond with bond order 1. On the other hand, in Au<sub>2</sub> with two unpaired electrons, the s-d hybridization prevails, because the relativistic contributions. A molecular orbital energy diagram for gas phase Au<sub>2</sub> is proposed, explaining its paramagnetism (and, by extension, the paramagnetism of gold clusters and nanoparticles).</p>

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