Thermal expansion and high-temperature phase transformation of the yttrium silicate Y₂SiO₅

Abstract

The linear thermal-expansion coefficients of yttrium silicate Y2SiO5, [Y2(SiO4)O] were measured in the temperature range from 20 to 1400 °C using x-ray diffraction. The anomalous behavior of thermal expansion was observed above Tc = 850 °C and was attributed to the displacive phase transformation. The transformation was reversible and resulted from the local order °C the compositional disorder and local fluctuation in the elastic free energy constrained a secondary transformation related to the polymorphic twin transformation. This created an additional peak in x-ray diffraction patterns at 2 's intensity. The characteristic of phase transformation both on heating and on cooling of the sample was also investigated using the differential thermal analysis method. The thermogravimetric technique did not indicate on a change of weight at Tc.

Effect of LiYO2 on the synthesis and pressureless sintering of Y2SiO5

“…These samples were examined by XRD for phase identification, and the results are summarized in Table I. Based on the XRD results, the exothermic peak at 834°C corresponded to the formation of Y 4.67 (SiO 4 ) 3 O, while the sharp exothermic peak at 960°C should originate from the presence of X1-Y 2 SiO 5 (a low-temperature polymorph of Y 2 SiO 5 , which can transform to high-temperature polymorph Y 2 SiO 5 at ≈850-1100°C; the reported transition temperatures vary 10,11,15 ). The only endothermic peak at 980°C was derived from the liquid-phase formation, and the broad exothermic peak between 987 and 1025°C corresponded to the formation of large amounts of Y 4.67 (SiO 4 ) 3 O and Y 2 SiO 5 .…”

“…9 Y 2 SiO 5 coatings can efficiently improve the hightemperature performance of silicon-based ceramics. 9,10 Unfortunately, preparation of single-phase Y 2 SiO 5 is very difficult because a strict stoichiometric ratio of the starting Y 2 O 3 /SiO 2 is needed. 7 At present, the sol-gel process and powder-mixing route have been used for the synthesis of Y 2 SiO 5 powders.…”

“…7 At present, the sol-gel process and powder-mixing route have been used for the synthesis of Y 2 SiO 5 powders. [10][11][12] In the sol-gel method, precursors of Y(NO 3 ) 3 13 It significantly lowered the sintering temperature of silicon nitride due to the presence of LiO 2 in the SiO 2 -Y 2 O 3 system, which led to formation of a low-viscosity liquid phase.…”

Recent progress on synthesis, multi-scale structure, and properties of Y–Si–O oxides

“…113,114 Therefore, the phase formation and stability, or the phase transition, still need to be studied. The main reason for this ambiguity is the susceptibility of yttrium silicates to the preparation method, impurity, and heating history.…”

Porous Y2SiO5 ceramics with a centrosymmetric structure produced by freeze casting

“…These silicates possess low oxygen permeability and a constant and suitable thermal expansion coefficient; thus, interest has been renewed in their potential applications in high-temperature structural ceramics, oxidation-protective coatings, and environmental barrier coatings [2][3][4][5]. In particular, Y 2 SiO 5 has an extremely low thermal conductivity, a low dielectric constant, a promising communication window, and can act as a thermal insulator material for the re-entry of space shuttles [6].…”