Review of Ag(Nb, Ta)O3 as a functional material

Valant, Matjaž; Axelsson, Anna‐Karin; Alford, Neil McN.

doi:10.1016/j.jeurceramsoc.2006.08.007

Cited by 109 publications

(77 citation statements)

References 47 publications

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“…1,2 Despite the technological importance of these materials, the structural origin of their high dielectric constants remains uncertain. Moreover, even the details of the crystal structures and phase transitions among the polymorphs of the endcompound AgNbO 3 remain a subject of debate.…”

Section: Introductionmentioning

confidence: 99%

Structural changes underlying the diffuse dielectric response inAgNbO3

et al. 2009

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Structural differences in the so-called M polymorphs of AgNbO 3 were analyzed using combined highresolution x-ray diffraction, neutron total scattering, electron diffraction, and x-ray absorption fine-structure measurements. These polymorphs all crystallize with Pbcm symmetry and lattice parameters ͱ2a c ϫ ͱ 2a c ϫ 4a c ͑where a c Ϸ 4 Å corresponds to the lattice parameter of an ideal cubic perovskite͒ which are determined by a complex octahedral tilt system ͑a − b − c − ͒ / ͑a − b − c + ͒ involving a sequence of two in-phase and two antiphase rotations around the c axis. Our results revealed that, similar to KNbO 3 , the Nb cations in AgNbO 3 exhibit local off-center displacements correlated along Nb-Nb-Nb chains. The displacements appear to be present even in the high-temperature AgNbO 3 polymorphs where the Nb cations, on average, reside on the ideal fixedcoordinate sites. The onset of the ͑a − b − c − ͒ / ͑a − b − c + ͒ tilting in the M polymorphs lifts the symmetry restrictions on the Nb positions and promotes ordering of the local Nb displacements into a long-range antipolarlike array. This ordering preserves the average Pbcm symmetry but is manifested in electron diffuse scattering and corroborated by other local-structure sensitive techniques. Structural states previously identified as the M 3 and M 2 phases represent different stages of displacive ordering rather than distinct thermodynamic phases. Rietveld refinements indicated intimate coupling between the displacive behavior on the oxygen, Nb, and Ag sublattices. The Pbcm symmetry of the octahedral framework precludes a complete ordering of Nb displacements so that some positional disorder is retained. This partial disorder likely gives a source to the dielectric relaxation which, according to previous spectroscopic studies, is the origin of the diffuse dielectric response exhibited by M-type AgNbO 3 at Ϸ250°C.

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Section: Introductionmentioning

confidence: 99%

Structural changes underlying the diffuse dielectric response inAgNbO3

et al. 2009

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“…[15][16][17][18] Moreover, density functional theory calculations predict that AgNbO 3 is a useful end member in PbO-free solid solutions for piezoelectric applications. 19 ATN solid solutions exhibit a complex sequence of tilting phase transitions.…”

Section: Introductionmentioning

confidence: 99%

Tilt transitions in compressively strained AgTa0.5Nb0.5O3thin fi

et al. 2011

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Phase transitions in coherently strained epitaxial AgTa ½ Nb ½ O 3 films grown on SrTiO 3 (001) substrates were characterized by high resolution X-ray diffraction and transmission electron microscopy. Coherently strained films were found to undergo the same phase transition sequence as bulk materials:. However, the compressive in-plane strain stabilized the tetragonal and orthorhombic phases, expanding these phase fields by ≈ 280 °C. The compressive strain state also favors c-axis domain texture. Consequently, unit cell quadrupling in the M 3 phase and the in-phase tilt of the T phase both occur around the out-of-plane direction. In contrast, bulk materials and relaxed films are poly-domain, with the complex tilt system occurring along all three of the orthogonal axes. Compressively strained films are in the M 3 phase at room temperature rather than in the M 2 phase as is observed in bulk. This suggests that strain not only modifies octahedral rotations but also disrupts the ordering of local cation displacements. These results demonstrate unambiguously that strain engineering in systems with complex tilt sequences such as AgTa ½ Nb ½ O 3 is feasible and open up the possibility of modifying properties by manipulation of the pertinent octahedral tilt transition temperature in a wide range of functional ceramics.

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“…AgTa x Nb 1-x O 3 perovskite solid solutions exhibit a rare combination of high but temperature stable dielectric constants and modest dielectric losses which renders them attractive candidates for high-frequency capacitors [1,2]. Despite the technological importance of these materials, the structural origin of their high dielectric constants remains uncertain.…”

Section: Introductionmentioning

confidence: 99%

Structural investigations of AgNbO<sub>3</sub> phases using high-energy X-ray diffraction

Yoneda

Yoshii

Kohara

2012

Trans. Mat. Res. Soc. Japan

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The perovskite ferroelectric system AgNbO 3 exhibits a successive phase transition. Recent synchrotron X-ray and neutron powder diffraction measurements have revealed a monoclinic phase remains down to low temperature. In the present work we describe a Rietveld analysis of the detailed structure in the wide temperature range. The structure analysis indicated a possibility that a rhombohedral structure exists in a temperature region lower than monoclinic structure. The monoclinic structure can be viewed as a condensation along one of the <110> direction of the local displacements present in the tetragonal phase. It equally well corresponds to a freezing-out of the local displacements along the <100> directions recently reported by Noheda et al. for PZT. The monoclinic structure therefore provides a microscopic picture in which one of the locally monoclinic phases in the average rhombohedral or tetragonal structures freezes out, and thus represents a bridge between two phases.

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Review of Ag(Nb, Ta)O3 as a functional material

Cited by 109 publications

References 47 publications

Structural changes underlying the diffuse dielectric response inAgNbO3

Structural changes underlying the diffuse dielectric response inAgNbO3

Tilt transitions in compressively strained AgTa0.5Nb0.5O3thin fi

Structural investigations of AgNbO<sub>3</sub> phases using high-energy X-ray diffraction

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