Solid solubility of Yb{sub 2}Si{sub 2}O{sub 7} in {beta}-, {gamma}- and {delta}-Y{sub 2}Si{sub 2}O{sub 7}

Journal Article · Fri Jul 15 00:00:00 EDT 2011 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2011.05.034· OSTI ID:21580153

Escudero, A ^[1]

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1. Bayerisches Geoinstitut, Universitaet Bayreuth, D-95440 Bayreuth (Germany)

This paper examines the structural changes with temperature and composition in the Yb{sub 2}Si{sub 2}O{sub 7}-Y{sub 2}Si{sub 2}O{sub 7} system; members of this system are expected to form in the intergranular region of Si{sub 3}N{sub 4} and SiC structural ceramics when sintered with the aid of Yb{sub 2}O{sub 3} and Y{sub 2}O{sub 3} mixtures. A set of different compositions have been synthesised using the sol-gel method to obtain a xerogel, which has been calcined at temperatures between 1300 and 1650 deg. C during different times. Isotherms at 1300 and 1600 deg. C have been analysed in detail to evaluate the solid solubility of Yb{sub 2}Si{sub 2}O{sub 7} in {beta}-Y{sub 2}Si{sub 2}O{sub 7} and {gamma}-Y{sub 2}Si{sub 2}O{sub 7}. Although Yb{sub 2}Si{sub 2}O{sub 7} shows a unique stable polymorph ({beta}), Yb{sup 3+} is able to replace Y{sup 3+} in {gamma}-Y{sub 2}Si{sub 2}O{sub 7} and {delta}-Y{sub 2}Si{sub 2}O{sub 7} at high temperatures and low Yb contents. IR results confirm the total solid solubility in the system and suggest a constant SiOSi angle of 180 deg. in the Si{sub 2}O{sub 7} unit across the system. The temperature-composition diagram of the system, obtained from powder XRD data, is dominated by the {beta}-RE{sub 2}Si{sub 2}O{sub 7} polymorph, with {gamma}-RE{sub 2}Si{sub 2}O{sub 7} and {delta}-RE{sub 2}Si{sub 2}O{sub 7} showing reduced stability fields. The diagram is in accordance with Felsche's diagram if average ionic radii are assumed for the members of the solid solution at any temperature, as long as the {beta}-{gamma} phase boundary is slightly shifted towards higher radii. - Graphical abstract: Polymorphism, as a function of average radii, in the systems Yb{sub 2}Si{sub 2}O{sub 7}-Y{sub 2}Si{sub 2}O{sub 7} (dotted symbols), Lu{sub 2}Si{sub 2}O{sub 7}-Y{sub 2}Si{sub 2}O{sub 7} (solid symbols) and Sc{sub 2}Si{sub 2}O{sub 7}-Y{sub 2}Si{sub 2}O{sub 7} (open symbols) compared to phase boundaries of Felsche for pure rare earth disilicates. Circles: {beta}-RE{sub 2}Si{sub 2}O{sub 7}. Squares: {gamma}-RE{sub 2}Si{sub 2}O{sub 7}. Triangles: {delta}-RE{sub 2}Si{sub 2}O{sub 7}. Highlights: > {beta}-Yb{sub 2}Si{sub 2}O{sub 7} and {beta}-Y{sub 2}Si{sub 2}O{sub 7} form a complete solid solution at 1300 deg. C. > Yb(III) replaces Y in {gamma}- and {delta}-RE{sub 2}Si{sub 2}O{sub 7}, at low Yb contents and high temperatures. > Phase diagram of the Yb{sub 2}Si{sub 2}O{sub 7}-Y{sub 2}Si{sub 2}O{sub 7} system is dominated by the {beta}-RE{sub 2}Si{sub 2}O{sub 7} phase. > {gamma}- and {delta}-phases show very reduced stability fields. > {beta}-{gamma} phase boundary in Felsche's diagram should be slightly shifted towards higher radii.

• OSTI ID: 21580153
• Journal Information: Journal of Solid State Chemistry, Vol. 184, Issue 7; Other Information: DOI: 10.1016/j.jssc.2011.05.034; PII: S0022-4596(11)00283-0; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

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37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ATOMIC RADII
CERAMICS
LUTETIUM SILICATES
PHASE DIAGRAMS
RARE EARTHS
SILICON CARBIDES
SILICON NITRIDES
SOL-GEL PROCESS
SOLID SOLUTIONS
SOLIDS
SOLUBILITY
STABILITY
TEMPERATURE RANGE 0400-1000 K
X-RAY DIFFRACTION
YTTERBIUM IONS
YTTERBIUM OXIDES
YTTRIUM IONS
YTTRIUM OXIDES
YTTRIUM SILICATES
CARBIDES
CARBON COMPOUNDS
CHALCOGENIDES
CHARGED PARTICLES
COHERENT SCATTERING
DIAGRAMS
DIFFRACTION
DISPERSIONS
ELEMENTS
HOMOGENEOUS MIXTURES
INFORMATION
IONS
LUTETIUM COMPOUNDS
METALS
MIXTURES
NITRIDES
NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
RARE EARTH COMPOUNDS
SCATTERING
SILICATES
SILICON COMPOUNDS
SOLUTIONS
TEMPERATURE RANGE
TRANSITION ELEMENT COMPOUNDS
YTTERBIUM COMPOUNDS
YTTRIUM COMPOUNDS