Thermophysical Properties of Rare-Earth-Stabilized Zirconia and Zirconate Pyrochlores as Surrogates for Actinide-Doped Zirconia

Abstract

Thermophysical properties of rare-earth-stabilized zirconia and zirconate pyrochlores, A 2 Zr 2 O 7 (A = La, Nd, Sm, Gd, Dy, Y), were evaluated by X-ray diffractometry, Raman spectroscopy, and the ultrasound pulse-echo method. Crystallographic analyses elucidated that had the pyrochlore structure, whereas Dy 2 Zr 2 O 7 and Y 2 Zr 2 O 7 had the defect fluorite structure. For lanthanide pyrochlores, the thermal expansion became smaller with increasing ionic radius of A and increasing crystal binding energy. The elastic moduli and Debye temperature evaluated using longitudinal and transverse sound velocities also depend on the ionic radius and binding energy, and hence these values related to mechanical properties increase with the ionic radius of A. On the other hand, Poisson's ratio was almost comparable among these pyrochlores. In addition, thermophysical properties of actinide pyrochlore are discussed in this study.

Lanthanum zirconate based thermal barrier coatings: A review

“…Shimamura et al reported that the lattice parameters of Ln2Zr2O7 pyrochlores increased with the ionic radius of Ln, as shown in Fig. 2 [18]. The lattice parameter of LZ is 10.8 Å in Shimamura's experiments and 10.802 Å in Tabira's work [21].…”

“…Two peaks, (331) and (511), shown in the LZ pattern originate from pyrochlore structure, and are also observed in Nd2Zr2O7, Sm2Zr2O7, and Gd2Zr2O7 patterns. Other peaks are commonly observed for the pyrochlore and defect fluorite structures [18]. Ln2Zr2O7 pyrochlore crystal is a cubic structure in space group 3 (origin choice 2) with four crystallographically independent atom sites (rear earth ion Ln, in 16d at ( , , ) , Zr in 16c at (0,0,0), O1 in 48f at (x, , ) and O2 in 8b at ( , , ).…”

“…[10,[16][17][18]. For thermal spray applications, 4 LZ powder can be synthesized by the solid state reaction method from a mixture of the lanthanum oxide (La2O3, 99.9%) and ZrO2 (99%) powders at high temperatures (1773 K) under an argon atmosphere for 10 hrs [16,17].…”

“…The remaining solid is then calcined at 900°C for 5 hrs. The sol-gel method is another way to synthesize nanostructured powders, which have high sintering ability for the A2Zr2O7 (A=La, Nd, Sm) system [18].…”

“…Fig. 1 shows the X-ray diffraction patterns of several Ln2Zr2O7 materials at room temperature [18]. Two peaks, (331) and (511), shown in the LZ pattern originate from pyrochlore structure, and are also observed in Nd2Zr2O7, Sm2Zr2O7, and Gd2Zr2O7 patterns.…”