In Situ Diffraction from Levitated Solids Under Extreme Conditions—Structure and Thermal Expansion in the Eu₂O₃–ZrO₂ System

Abstract

The accurate determination of structure and thermal expansion of refractory materials at temperatures above 1500°C is challenging. Here, for the first time, we demonstrate the ability to reliably refine the structure and thermal expansion coefficient of oxides at temperatures to 2200°C using in situ synchrotron diffraction coupled with aerodynamic levitation. Solid solutions in the Eu 2 O 3 -ZrO 2 binary system were investigated, including the high-temperature order-disorder transformation in Eu 2 Zr 2 O 7 . The disordered fluorite phase is found to be stable above 1900°C, and a reversible phase transition to the pyrochlore phase is noticed during cooling. Site occupancies in Eu 2 Zr 2 O 7 show a gradual increase in disorder on both cation and anion sublattices with increasing temperature. The thermal expansion coefficients of all cubic solid solutions are relatively similar, falling in the range 8.6-12.0 3 10 -6 C -1 . These studies open new vistas for in situ exploration of complex structural changes in high-temperature materials.

Crystal structure analysis of <i>Ln</i>₂Zr₂O₇ (<i>Ln</i> = Eu and La) with a pyrochlore composition by high-temperature powder X-ray diffraction

“…As the behavior of the thermal expansion coefficients calculated from the lattice constants for EZO of Maram et al 14) clearly disagreed with that in this work, the results of them are not shown in this figure. Similarly, the results of previous study 5) are not shown in this figure too.…”

“…Figure 3 represents the temperature dependence of the lattice constants of EZO estimated from the Rietveld analyses. The results of Kutty et al, 18) Maram et al 14) and Hagiwara et al 5) are also shown in the figure for comparison. As compared with previous results, 5) the slope of EZO prepared in this work was larger than that.…”

“…However, the lattice constants of EZO prepared in this work were smaller than those reported by Kutty et al As shown by ICP-AES, EZO prepared in this work was rich in Zr (Eu:Zr = 49.1 mol %:50.9 mol %). We thought that Zr 4+ , which has a the small cation radius (0.084 nm), 16) 14) used an unconditioned beam from a 250 W CO 2 laser for sample heating and an optical pyrometer for measuring samples temperatures. It is difficult to compare simply the results of the lattice constant of EZO because of the differences in the measuring conditions and methods.…”

Calorimetric study of Eu2O3–ZrO2 feedstock powders and sintered materials

“…6) 1200°C. However, even in stoichiometric Eu zirconate sintered at 1300°C, the relative intensity of superstructure peaks was relatively low [18], while in [19] fully ordered europium zirconate was obtained after synthesis at 1400°C. In the present study, the temperature of additional heat treatment was 1450°C which is enough to form ordered pyrochlore from defected fluorite.…”

Drop‐and‐catch (DnC) calorimetry using aerodynamic levitation and laser heating

“…Rock Thermochemistry Laboratory at UC Davis to be used together with an existing 400 W CO 2 laser system, conventional aerodynamic levitator, CCD camera, and laser melting stage. Systems for laser melting of the powders and aerodynamic levitation are commercially available (Materials Development, Inc., Evanston, IL, USA) and employed at neutron and synchrotron sources for high‐temperature diffraction on melts and solids and will not be described in detail. The main components of the DnC are shown on Fig.…”