Crystal structure analysis of <i>Ln</i><sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> (<i>Ln</i> = Eu and La) with a pyrochlore composition by high-temperature powder X-ray diffraction


We synthesized Eu2Zr2O7 and La2Zr2O7 using high purity ZrO2 of extremely low Hf content. The crystal structures of Eu2Zr2O7 and La2Zr2O7 were refined by the Rietveld analysis of the powder X-ray diffraction data (indexed as a cubic pyrochlore-type structure, space group: No.227, Fd3m) measured from 1173 to 298 K in a dry condition and from 1173 to 323 K in a wet condition. The crystal structure of La2Zr2O7 is near to an ideal pyrochlore-type structure, whereas that of Eu2Zr2O7 is a distorted pyrochlore-type structure. The thermal expansion coefficients of Eu2Zr2O7 were larger than those of La2Zr2O7. The value of the equivalent isotropic atomic displacement parameters (Beq) calculated from the anisotropic atomic displacement parameter for the Zr in Eu2Zr2O7 at 298 K was around 1.4 Å2, and the increase of this value in Eu2Zr2O7 with increasing temperature was smaller than that in La2Zr2O7.


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