The Ferroelectric Non-Stoichiometric LiTaO3-Type Phases

Ravez, J.; Joo, Gi−Tae; Senegas, J.; Hagenmuller, Pascal

doi:10.7567/jjaps.24s2.1000

Cited by 14 publications

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“…La temperatura de Curie decrece al aumentar la concentración del dopante. Con Al 3+ se reportan soluciones sólidas con LiTaO 3 , de acuerdo con los resultados anteriores, la línea con mayor límite de solubilidad es la estequiométrica (72,75). En este caso la temperatura de Curie desciende conforme aumenta la concentración de Al 3+ , esto ocurre en una línea no estequiométrica (76).…”

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Estudio de las soluciones de los ferroeléctricos LiNbO3 y LiTaO3

Castrejón¹

2002

Bol. Soc. Esp. Ceram. Vidr.

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Los compuestos cerámicos LiNbO 3 y LiTaO 3 han sido estudiados considerablemente en los últimos años, debido a las interesantes propiedades ópticas y eléctricas (piezoelectricidad, piroelectricidad, ferroelectricidad) que presentan. Por estas razones estos materiales se consideran excelentes candidatos para un gran número de aplicaciones tecnológicas. Una característica importante de estos compuestos, es la facilidad con la que forman series de soluciones sólidas, incorporando diferentes cationes en sus redes. Se han obtenido series de soluciones sólidas con cationes de diferente tamaño y diferente carga con la consiguiente variación de las propiedades eléctricas y ópticas. En este trabajo se presenta un resumen de los estudios de las soluciones sólidas de LiNbO 3 y LiTaO 3 , los mecanismos de formación y los sitios que ocupan los cationes en la celda unidad, así como algunas de sus propiedades físicas más representativas Palabras clave: Niobato de litio, tantalato de litio, soluciones sólidas, ferroeléctricos Study of the ferroelectric LiNbO 3 and LiTaO 3 solid solutionsCeramic compounds LiNbO 3 and LiTaO 3 have been widely studied in the last years due to their interesting optical and electrical properties (piezoelectricity, piroelectricity, ferroelectricity). For this reason these materials are regarded excellent candidates for technological applications. An important characteristic of these compounds is the facility to form solid solution series, a large number of cations can be accommodated in the lattice and thus different optical and electrical properties have been obtained. In this work a review of LiNbO 3 and LiTaO 3 solid solutions is presented, the formation mechanisms, cation sites in the unitcell and some of the most representative properties are also included. Keywords INTRODUCCIÓNEl LiNbO 3 y el LiTaO 3 son compuestos muy versátiles. Desde los años setenta se han estudiado por sus numerosas aplicaciones y propiedades. En los ochenta, el enfoque principal se centró en los efectos producidos por la introducción de diversos cationes en solución sólida. En la última década se ha usado extensamente la técnica EXAFS (X ray absortion fine structure), además de méto-dos de simulaciones, para determinar los sitios que ocupan en la red estos diferentes cationes que forman las soluciones sólidas (1, 2).Actualmente el interés principal es el establecer una correlación entre los defectos provocados en estas redes al introducir diferentes cationes y los cambios en las propiedades físicas antes mencionadas.En principio, la determinación de los sitios que ocupan los cationes adicionados para formar soluciones sóli-das en estos materiales no es un problema sencillo, debido a la estructura pseudo-ilmenita que presentan. Esta estructura, descrita por diversos autores (3, 4), puede considerarse como una superestructura del corindón, en la que se reemplazan dos Al 3+ por un Li + y un Ta 5+, la cual está formada por cadenas de octaedros que comparten las caras a lo largo del eje polar c (Fig.1). 325Figura 1. Estructur...

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Estudio de las soluciones de los ferroeléctricos LiNbO3 y LiTaO3

Castrejón¹

2002

Bol. Soc. Esp. Ceram. Vidr.

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“…Past NMR studies of lithium niobate and tantalate have focused on a detailed characterization of the nuclear electric quadrupolar interaction of 7 Li and 93 Nb, with the primary goal of developing a structural description of nonstoichiometry in lithium niobate. − Preliminary data concerning site distribution and atomic mobility of lithium have also been published for congruent and nonstoichiometric lithium niobate , and tantalate . In addition, the atomic distribution of various ternary solid solution systems has been examined on the basis of 7 Li line shape analysis; however to the best of our knowledge, no solid-state NMR studies of lithium niobate−tungsten oxide solid solutions have appeared in the literature. The present paper presents a host of complementary experiments carried out on Li 1 - x Nb 1 - x W x O 3 samples with variable substitution level x , resulting in a more detailed understanding of structure and ionic motion in these materials.…”

Section: Introductionmentioning

confidence: 99%

⁷Li and ⁶Li Solid-State NMR Studies of Structure and Dynamics in LiNbO₃−WO₃ Solid Solutions

Yin

Machida

et al. 1997

J. Phys. Chem. B

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The spatial distribution and atomic mobility of Li ions in the solid solution system Li1 - x Nb1 - x W x O3 (0 ≤ x ≤ 0.5) have been studied using solid-state NMR techniques. To maintain charge balance, for each tungsten atom substituting on a niobium site, a lithium vacancy is produced in the lithium sublattice. 6Li magic angle spinning experiments reveal multiple lithium sites, attributed to distributions of niobium and tungsten neighbors. Dipolar 7Li second moments measured at low temperature (−100 °C) depend linearly on lithium content, consistent with a random distribution of vacancies. Variable temperature (−20 to 550 °C) 7Li NMR studies as a function of composition give evidence for two distinct motional processes: at low temperatures (near 0 °C) a local hopping process involving only a minority of the lithium ions present is activated. At high temperatures (300 °C and above, depending on substitution levels) long-range diffusion involving all the lithium atoms is evident on the NMR time scale. As the substitution level x is increased, the long-range mobility of lithium increases. In contrast, the number of lithium atoms participating in the low-temperature process and their respective mobilities reach a maximum near x = 0.25. This result is explained on the basis of detailed simulations, considering favorable cation transport mechanisms through intrinsic vacancies of the LiNbO3 lattice. Both the 6Li line shape and the 7Li dynamics simulations are consistent with a statistical distribution of Nb and W atoms and formation of W-vacancy pairs along the c-axis.

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“…A lot of work has been undertaken on single crystals, however, ceramics of this ferroelectric family had not been developed because of the required high sintering temperature (> 1300oC) leading to the volatilisation of Li20. Systematic research has been undertaken recently by the way of oxide or fluoride addition or by sol-gel preparation process, in order to improve the ceramic qualities (1)(2)(3)(4). Satisfying results have been obtained, amongst which the addition of litium and magnesium fluorides has permitted to prepare highly densified LiNbO3 or LiTa03-type ceramics by sintering in free atmosphere at a temperature of 900oC (2,3).…”

Section: Introductionmentioning

confidence: 99%

Sintering mechanism of LiTaO/sub 3/ ceramics by the addition of lithium and magnesium fluorides

Mühll²,

Ravez³

[Proceedings] 1990 IEEE 7th International Symposium on Applications of Ferroelectrics

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Highly densified LiNbO3 and LiTa03 ceramics have been obtained by sintering in a moist atmosphere in the presence of LiF and MgF2. The sintering temperatures was decreased by 300oC for LiNbO3 and 500oC for LiTa03. An open air sintering mechanism based on the partial hydrolysis of the starting fluorides and the formation of an intermediate MgqM2Xg (M = Li,Ta; X = O,F,OH) type hydroxofluoride phase, has been proposed and a three stage reactional sketch has been given.1.Introduction LiNb03 and LiTa03 are well known by their interesting non-linear properties, such as piezo-and pyroelectricity, electrooptics, etc. A lot of work has been undertaken on single crystals, however, ceramics of this ferroelectric family had not been developed because of the required high sintering temperature (> 1300oC) leading to the volatilisation of Li20. Systematic research has been undertaken recently by the way of oxide or fluoride addition or by sol-gel preparation process, in order to improve the ceramic qualities (1-4). Satisfying results have been obtained, amongst which the addition of litium and magnesium fluorides has permitted to prepare highly densified LiNbO3 or LiTa03-type ceramics by sintering in free atmosphere at a temperature of 900oC (2, 3). Dielectric, piezo-and pyroelectric measurements on LiTa03 ceramics showed that the ferroelectric Curie temperature is higher than that of pure LiTa03 and that piezo-and pyroelectric coefficients reach respectively 20% and 30% of the values of LiTa03 single crystals. These piezo-and pyroelectric properties are the best performances so far realized on LiTa03-type ceramics (Table 1). In this paper the sintering mechanism of LiTaO and MgF2 will be reported.ceramics at low temperatures in the presence of Li 8 2.Substantial Comparative Sintering Effects Highly densified ceramics were prepared by sintering at 900OC in air atmosphere the mixtures: (1-x)LiM03 + x(LiF+MgF2) (M=Nb; Ta). Figure 1 shows the thermal evolution of the thickness of a cylindrical sample made of compacted powder of starting composition x = 0.05, recorded by means of a 0-7803-0190-0/91$01 .OO OIEEE Netzsch differential dilatometer. As a comparison, the curves of pure LiNb03 and LiTa03 samples are also given. I1 can be seen that the addition of small amounts of the lithium and magnesium fluorides decreased the sintering temperature by 300 degrees for LiNb03 and by 500 degrees for LiTa03. 3.Experimental Studies Revealing the Sintering Mechanism 3.1 Air atmosphere conditionsA quite different behaviour of the (l-x)LiTa03 + x(LiF+MgFZ) mixtures at 900oC was observed according to the atmosphere. A previous study carried out on the same starting compositions but in sealed platinium tubes showed that the obtained samples were poorly densified at 900OC (the shrinkage coefficient Ad/# e 0.01 !) (14). Further experiments showed that the level of moisture in the atmophere greatly influenced the sintering process.Water vapour seems to promote the partial hydrolysis of the additive fluorides, particularly that . A high-temperature X...

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The Ferroelectric Non-Stoichiometric LiTaO₃-Type Phases

Cited by 14 publications

References 0 publications

Estudio de las soluciones de los ferroeléctricos LiNbO<sub>3</sub> y LiTaO<sub>3</sub>

Estudio de las soluciones de los ferroeléctricos LiNbO<sub>3</sub> y LiTaO<sub>3</sub>

⁷Li and ⁶Li Solid-State NMR Studies of Structure and Dynamics in LiNbO₃−WO₃ Solid Solutions

Sintering mechanism of LiTaO/sub 3/ ceramics by the addition of lithium and magnesium fluorides

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The Ferroelectric Non-Stoichiometric LiTaO3-Type Phases

Cited by 14 publications

References 0 publications

Estudio de las soluciones de los ferroeléctricos LiNbO<sub>3</sub> y LiTaO<sub>3</sub>

Estudio de las soluciones de los ferroeléctricos LiNbO<sub>3</sub> y LiTaO<sub>3</sub>

7Li and 6Li Solid-State NMR Studies of Structure and Dynamics in LiNbO3−WO3 Solid Solutions

Sintering mechanism of LiTaO/sub 3/ ceramics by the addition of lithium and magnesium fluorides

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The Ferroelectric Non-Stoichiometric LiTaO₃-Type Phases

⁷Li and ⁶Li Solid-State NMR Studies of Structure and Dynamics in LiNbO₃−WO₃ Solid Solutions