Crystal Structure of Orthorhombic CaTa2O6.

Jahnberg, Lena; Hersh, L. S.; Toguri, J. M.; Hedberg, Kenneth; Trætteberg, M.

doi:10.3891/acta.chem.scand.17-2548

Cited by 70 publications

(34 citation statements)

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“…In the case of CaTa 2 O 6 , ceramic materials prepared at about 1550À1600°C and slowly cooled down to room temperature (cooling rates are typically 1À2°C/min) yield the orthorhombic aeschynite structure (Pnma space group). The crystal structure, 7 microwave dielectric response, 1,2 and vibrational (through unpolarized Raman and infrared spectroscopies) 10 of the aeschynite CaTa 2 O 6 polymorph have been previously reported. Although a complete determination of the phonon modes for this structure is still lacking, the published results are able to reasonably account for the main dielectric properties required for microwave applications of the material.…”

Section: Articlementioning

confidence: 99%

Raman and Infrared Phonon Features in a Designed Cubic Polymorph of CaTa₂O₆

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Lobo

et al. 2011

Crystal Growth & Design

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At room temperature, calcium tantalite (CaTa 2 O 6 ) is known to exhibit three stable polymorphs, depending on the crystal growth conditions. In this work, the laser-heated pedestal growth method was used to obtain CaTa 2 O 6 single crystal fibers in its quenched (ordered) cubic polymorph, attractive for optical applications. X-ray diffraction, Raman scattering and infrared spectroscopy showed that the fibers grew into the centrosymmetrical Pm3 space group. The growth axis was determined as [001]. The cylindrical fibers (20 mm long and 400 μm wide) showed good optical quality, without cracks or striations, but with small facets, parallel to crystal edges or to in-plane edge bicetrices. A comprehensive set of the optical phonons for this cubic structure was obtained, consisting of 13 (of 16 foreseen) triply degenerate polar phonons, and all the 21 predicted Raman modes. By using special scattering geometries, the Raman bands were attributed to their corresponding irreducible representations. In general, the phonons showed rather large damping constants, which do not compromise the designed optical applications in compact lasers but increase the losses in the microwave range, even though the dielectric response is quite adequate for microwave applications. Quenched defects and crystal polymorphism can be at the origin of the large phonon damping.

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Section: Articlementioning

confidence: 99%

Raman and Infrared Phonon Features in a Designed Cubic Polymorph of CaTa₂O₆

Teixeira

Moreira

Lobo

et al. 2011

Crystal Growth & Design

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“…The type of pairs of edge-linked octahedra described above can be recognized in many structures such as CaTa206 (Jahnberg, 1963) and K~Nb60~7 (Gasperin & Le Bihan, 1982). However, the pairs of octahedra in the former compound are coupled proposed.…”

Section: Resultsmentioning

confidence: 99%

Studies of K₃Nb₇O₁₉ by high-resolution electron microscopy and X-ray powder diffraction

Sundberg¹,

Lundberg²

1987

Acta Crystallogr Sect B

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An idealized structure model of the K3Nb7Ol9 compound has been deduced from high-resolution electron micrographs. For simplicity the structure was derived in a pseudo-monoclinic system with triclinic symmetry (space group P1) and unit-cell dimensions a = 13.777 (2), b =6-431 (1), c= 18.897 (6) A, a-~ 90, /3 = 98.06 (2) and y -~ 90 °, V = 1657.7 A 3, Z = 4. It has been verified both by simulated image calculations in two projections and by X-ray powder diffraction studies. The structure consists of a threedimensional framework which is built up of pairs of NbO6 octahedra having one edge in common in such a way that the structure can be described by means of{011} crystallographic shear in the ReO3 type structure. The pairs are linked by edge and corner sharing as in the {120} crystallographic-shear (CS) structure M702o. Two kinds of tunnels are formed, in which the K atoms are located. The structure thus independently derived agrees with that recently published by triclinic. We have refined the cell parameters given in that article: a = 14.1282 (9), b--9.9369 (9), c = 6.4553 (6) A, a= 106.44(1), /3=95.856(6) and y= 97.30 (1) °, V= 853.05 ~3, Z =2, M~ = 1071.64, and Dx = 4.17 g cm -3. However, in this paper the structure is described in a different manner and discussed in relation to neighbouring compounds of this system.

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“…The entry of a large amount of food into the stomach leads to adaptive (or receptive) relaxation of the proximal part of the stomach acting as a reservoir (Jahnberg, 1977). The rhythmic contractions of the distal stomach are thought to control the trituration and emptying of solids, whereas the tonic contractions of the proximal stomach govern the rate of emptying of liquids.…”

Section: Relationships Between Motility and Flow Of Digesta Stomachmentioning

confidence: 99%