An Approach To The Defect Structure Analysis Of Lithium Niobate Ilmenite Type Structure

We present in this work a comparative study between the normal and the ilmenite structural of LiNbO3. Namely, the normal cation stacking sequence is replaced by the ilmenite ordering: …Nb Li vacancy Li Nb vacancy Nb Li vacancy Li Nb vacancy…. . From Safaryan’s approach which combines a ferroelectric phase transition theory and vacancy models we allows to calculate the Curie temperature in ilmenite LiNbO3. Comparatively, we showed that the ilmenite structural LiNbO3 is in an excellent agreement with experiment result than the normal LiNbO3We present in this work a comparative study between the normal and the ilmenite structural of LiNbO3. Namely, the normal cation stacking sequence is replaced by the ilmenite ordering: …Nb Li vacancy Li Nb vacancy Nb Li vacancy Li Nb vacancy…. . From Safaryan’s approach which combines a ferroelectric phase transition theory and vacancy models we allows to calculate the Curie temperature in ilmenite LiNbO3. Comparatively, we showed that the ilmenite structural LiNbO3 is in an excellent agreement with experiment result than the normal LiNbO

An Approach To The Defect Structure Analysis Of Niobate And Tantalate Lithium Ilmenite Type Structure

We present in this work a comparative study between normal LiNbO3 (LiTaO3) and ilmenite structural LiNbO3 (LiTaO3). Namely, the normal cation stacking sequence is replaced by ilmenite ordering …Nb (Ta) Li vacancy Li Nb (Ta) vacancy Nb (Ta) Li vacancy Li Nb (Ta) vacancy… From Safaryan’s approach which combines a ferroelectric phase transition theory and vacancy models we calculated the Curie temperature in ilmenite LiNbO3 (LiTaO3). Comparatively, we showed that the ilmenite structural LiNbO3 (LiTaO3) is in an excellent agreement with experiment result than normal LiNbO3 (LiTaO3).We present in this work a comparative study between normal LiNbO3 (LiTaO3) and ilmenite structural LiNbO3 (LiTaO3). Namely, the normal cation stacking sequence is replaced by ilmenite ordering …Nb (Ta) Li vacancy Li Nb (Ta) vacancy Nb (Ta) Li vacancy Li Nb (Ta) vacancy… From Safaryan’s approach which combines a ferroelectric phase transition theory and vacancy models we calculated the Curie temperature in ilmenite LiNbO3 (LiTaO3). Comparatively, we showed that the ilmenite structural LiNbO3 (LiTaO3) is in an excellent agreement with experiment result than normal LiNbO3 (LiTaO3)

New Study Of Electrical Conductivity In Ni-Doped Non -Stoichiometric Lithium Tantalite

Electrical conductivity in Ni-doped nonstoichiometric lithium tantalite was described by a new theoretical approach. From the experience, we have proposed the new vacancy models which are able to describe substitutional mechanism in Ni-doped lithium tantalite. A combinaison of phase transition theory and generalised vacancy models allows us to establish a new expression of electrical conductivity which takes into account the defect structure of Ni-doped lithium tantalate. Calculations of the conductivity in Ni-doped nonstoichiometric lithium tantalate reveal good correspondence with experimental results.Electrical conductivity in Ni-doped nonstoichiometric lithium tantalite was described by a new theoretical approach. From the experience, we have proposed the new vacancy models which are able to describe substitutional mechanism in Ni-doped lithium tantalite. A combinaison of phase transition theory and generalised vacancy models allows us to establish a new expression of electrical conductivity which takes into account the defect structure of Ni-doped lithium tantalate. Calculations of the conductivity in Ni-doped nonstoichiometric lithium tantalate reveal good correspondence with experimental results

Experimental And Theoretical Study Of The Substitution Mechanism In The W6+: Litao3 Correlated With The Ferroelectric Properties

The purpose of the present work is to report the latest results of our experimental and theoretical non-stoichiometry investigations of solid solutions isolated close to LiTaO3 inside the ternary system Li2O-Ta2O5-(WO3)2 correlated with the ferroelectrics transitions. Dielectric measurements performed on ceramic samples have shown that ferro-paraelectric temperatures transitions TC varied along the solids solutions, as the stoichiometry deviates from LiTaO3. A Safaryan’s theory of ferroelectric transition and the various vacancy models in this work reproduce well the experimental results by explaining the substitution nature of Tungsten hexavalent (W6+) in LiTaO3.The purpose of the present work is to report the latest results of our experimental and theoretical non-stoichiometry investigations of solid solutions isolated close to LiTaO3 inside the ternary system Li2O-Ta2O5-(WO3)2 correlated with the ferroelectrics transitions. Dielectric measurements performed on ceramic samples have shown that ferro-paraelectric temperatures transitions TC varied along the solids solutions, as the stoichiometry deviates from LiTaO3. A Safaryan’s theory of ferroelectric transition and the various vacancy models in this work reproduce well the experimental results by explaining the substitution nature of Tungsten hexavalent (W6+) in LiTaO3

Analytical and experimental study of electrical conductivity in the lithium tantalate nonstoichiometric structure

We have been interested to experimental and analytical studies of ionic conductivity of nonstoichiometric LiTaO3 solid solutions. Theoretical approach combined with lithium and tantalate vacancy models has been performed. A comparative study between the calculated and measured values is presented taking into account the temperature and composition effects on the conductivity.We have been interested to experimental and analytical studies of ionic conductivity of nonstoichiometric LiTaO3 solid solutions. Theoretical approach combined with lithium and tantalate vacancy models has been performed. A comparative study between the calculated and measured values is presented taking into account the temperature and composition effects on the conductivity

Polya's inequalities, global uniform integrability and the size of plurisubharmonic lemniscates

First we prove a new inequality comparing uniformly the relative volume of a Borel subset with respect to any given complex euclidean ball \B \sub \C^n with its relative logarithmic capacity in \C^n with respect to the same ball \B. An analoguous comparison inequality for Borel subsets of euclidean balls of any generic real subspace of \C^n is also proved. Then we give several interesting applications of these inequalities. First we obtain sharp uniform estimates on the relative size of \psh lemniscates associated to the Lelong class of \psh functions of logarithmic singularities at infinity on \C^n as well as the Cegrell class of \psh functions of bounded Monge-Amp\`ere mass on a hyperconvex domain \W \Sub \C^n. Then we also deduce new results on the global behaviour of both the Lelong class and the Cegrell class of \psh functions.Comment: 25 page

Nouvelle approche de modélisation de milieux poreux. Application à l'os trabéculaire

Dans de nombreux domaines tels que la science des matériaux ou l'imagerie médicale, il est intéressant d'évaluer les propriétés mécaniques d'une structure. Pour ce faire, l'analyse par éléments finis est souvent utilisée. Cependant, son application à des milieux poreux complexes est limitée, car le nombre d'éléments nécessaires pour représenter la structure interne est très grand. Dans cette communication, nous proposons une nouvelle approche par éléments finis qui prend en compte la topologie de la structure étudiée. Pour cela, nous implémentons et améliorons une technique récente basée sur le squelette 3D, permettant de caractériser des milieux poreux complexes. Chaque travée de la structure interne peut alors être représentée par une chaîne de poutres rectilignes auxquelles sont attribuées les propriétés de l'arche. Cette approche permet de réduire considérablement le temps de calcul nécessaire à la simulation mécanique par éléments finis tout en présentant une bonne adéquation avec une technique de référence. Nous avons évalué cette technique sur des vecteurs de test, puis appliqué notre méthode sur des échantillons d'os trabéculaire afin d'en quantifier précisément l'élasticité. Ce nouveau procédé de modélisation donne de meilleurs résultats de rigidité par rapport aux techniques à éléments poutre existantes sur des vecteurs de test. Cette tendance se confirme également lors de son application à l'étude de la microarchitecture de l'os trabéculaire

Relation entre la régularité de fractals 3D et celle de leurs projections 2D. Application à l'os trabéculaire

Deux des auteurs ont récemment établi que la régularité Rn d'un fractal continu isotrope de dimension n (nD) est égale à celle sa projection Rn-1 dans un espace (n-1)D diminuée de 0.5, ou plus clairement, Rn = Rn-1 - 0.5. Dans un premier temps, l'objectif de cette étude est d'expliquer brièvement ce résultat et de l'illustrer sur des volumes fractals synthétiques, continus et binaires, et leurs projections. Pour les fractals continus, les résultats sont proches de eux qu'il convient de trouver pour H faible. Pour H élevé, il apparaît des difficultés liées essentiellement aux défauts de la méthode de synthèse retenue. Pour les fractals binaires, l'écart de 0.5 qu'il est possible de trouver entre la régularité du volume et celle de sa projection n'est pas clairement établie. Dans un deuxième temps, nous avons expérimentalement étudié si cette relation est valide pour l'os trabéculaire et sa projection. Nous avons analysé 22 échantillons de tête de fémur imagés par micro-scanner. Nous trouvons une différence entre la régularité 2D et celle en 3D de 0.53 ± 0.046. Ceci indique que le la relation qui lie la régularité 3D d'un volume fractal à celle de sa projection s'applique pour cet objet binaire. Une simple mesure 2D permettrait alors de quantifier la structure trabéculaire 3D et pourrait se révéler d'une grande force pour le diagnostic précoce de l'ostéoporose