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, Journal Name: Journal of Solid State Chemistry Journal Issue: 7 Vol. 184; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

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