Structural and Crystal Chemical Investigation of Intermediate Phases in the System Ca sub(2)SiO sub(4)-Ca sub(3)(PO sub(4)) sub(2)-CaNaPO sub(4)

Two intermediate compounds of the system Ca sub(2)SiO sub(4)-Ca sub(3)(PO sub(4)) sub(2)-CaNaPO sub(4) were synthesized by reaction sintering at 1600 degree C and analyzed structurally, chemically, and optically. The structure of Ca sub(7)(PO sub(4)) sub(2)(SiO sub(4)) sub(2) nagelschmidtite (space...

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Bibliographic Details
Published in:Journal of the American Ceramic Society 2015-12, Vol.98 (12), p.3956-3965
Main Authors: Widmer, Remo, Gfeller, Frank, Armbruster, Thomas
Format: Article
Language:English
Subjects:
Binary systems (materials)
Ceramics
Diffraction
Phases
Quenching
Silicon dioxide
Solid solutions
X-rays
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Summary:Two intermediate compounds of the system Ca sub(2)SiO sub(4)-Ca sub(3)(PO sub(4)) sub(2)-CaNaPO sub(4) were synthesized by reaction sintering at 1600 degree C and analyzed structurally, chemically, and optically. The structure of Ca sub(7)(PO sub(4)) sub(2)(SiO sub(4)) sub(2) nagelschmidtite (space group P6 sub(1), a = 10.7754(1) Aa, c = 21.4166(3) Aa) was determined by single crystal X-ray analysis. Its unit cell can be interpreted as a supercell ( approximately 2 a, 3 c) of the high-temperature polymorph alpha -Ca sub(2)SiO sub(4). Evidence for pseudo-hexagonal symmetry is shown. Using electron microprobe, the solid solution Ca sub(7-x)Na sub(x)(PO sub(4)) sub(2+x)(SiO sub(4)) sub(2-x), (x less than or equal to 2), of nagelschmidtite was confirmed. Volume thermal expansion coefficients of Ca sub(6.8)Na sub(0.2)(PO sub(4)) sub(2.2)(SiO sub(4)) sub(1.8) and Ca sub(5.4)Na sub(1.5)(PO sub(4)) sub(3.7)(SiO sub(4)) sub(0.3) were determined using high-temperature X-ray powder diffraction, yielding mean alpha sub(V)= 3. 95 and 5.21 [10 super(-5 )/ degree C], respectively. Ca sub(15)(PO sub(4)) sub(2 )(SiO sub(4)) sub(6) is a distinct phase in the binary section Ca sub(2)SiO sub(4)-Ca sub(3)(PO sub(4)) sub(2) and was found to extend into the ternary space according to Ca sub(15-x)Na sub(x)(PO sub(4)) sub( 2+x)(SiO sub(4)) sub(6-x), (x less than or equal to 0.1). Quenching experiments of the latter allowed for structural analysis of a strongly disordered, defective high-temperature polymorph of the alpha -Ca sub(2)SiO sub(4)- alpha -Ca sub(3)(PO sub(4 )) sub(2) solid solution. Structural relations between nagelschmidtite, Ca sub(15)(PO sub(4)) sub(2 )(SiO sub(4)) sub(6) and the end-member compounds of the system are discussed.
ISSN:0002-7820
1551-2916
DOI:10.1111/jace.13850