2013
ACL
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A.J.Fernández-Carrión, M.Allix, A.I.Becerro, 'Thermal Expansion of Rare Earth Pyrosilicates', J. Am. Ceram. Soc. 96 2298 (2013) doi:10.1111/jace.12388
The use of RE2Si2O7 materials as environmental barrier coatings and in the sintering process of advanced ceramics demands a precise knowledge of the coefficient of thermal expansion of the
RE2Si2O7. The literature on this subject is extremely scarce and the present study has been conducted to fill in this gap. High temperature X-ray diffraction patterns were collected on different RE2Si2O7 polymorphs (RE = La, Pr, Nd, Gd, Dy, Ho, Er, Yb, Lu and Sc), namely A, G, α, β, γ, and δ, to determine the changes in unit cell dimensions. RE2Si2O7 compounds belonging to the same polymorph showed, qualitatively, very similar unit cell parameters behaviour with temperature, while the different polymorphs of a given RE2Si2O7 compound exhibited markedly different thermal expansion evolution.
The isotropy of thermal expansion was demonstrated for the A-RE2Si2O7 polymorph while the G, α, β, γ, and δ polymorphs exhibited an anisotropic unit cell expansion with the biggest expansion directed along the REOx polyhedral chains. The coefficients of thermal expansion were calculated from the unit cell volume expansion for each RE2Si2O7 compound. All compounds belonging to the same polymorph exhibited similar apparent bulk coefficients of thermal expansion (ABCTE) values, and no evident relationship between ionic radius and ABCTE within the same polymorph was observed. However, the ABCTE values differ significantly from one polymorph to the other. The highest ABCTE values correspond to A-RE2Si2O7 compounds, with an average of 12.1*10-6 K-1 while the lowest values are those of β- and γ-RE2Si2O7, which showed average ABCTE values of ~4.0*10-6 K-1.
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