Incommensurately modulated ZrO2-xF2x

Abstract

The compound ZrO2-xF2x has been studied by X-ray powder diffraction and transmission electron microscopy. It was previously described as a series of anion-deficient, α-UO3-type "line phases," with compositions in between resulting from unit cell scale intergrowths of the line phases. More correctly ZrO2-xF2x is described as an incommensurately modulated structure with composition-dependent primary modulation wave-vector, q = xb*. The underlying orthorhombically distorted α-UO3-type parent structure has space group symmetry Cmmm (a ≈ 6.44, b ≈ 3.83, c ≈ 4.07 Å). Characteristic extinction conditions imply a superspace group symmetry of P:Cmmm:s, -1,1. The previously reported crystal structure of Zr7O9F10 is Fourier decomposed in these terms. Crystal chemical reasons are proposed for the very limited composition range, 0.698 ≤ x ≤ 0.714, observed for the title compound. Show more