Structural Effects of Cu/Zn Substitution in the Malachite–Rosasite System

Abstract

AbstractSynthetic zincian malachite samples (Cu1–xZnx)2(OH)2CO3withx= 0, 0.1, 0.2 and 0.3 were characterized by powder X‐ray diffraction and optical spectroscopy. The XRD patterns of the samples up tox= 0.2 indicate single phase materials with an approximately linear dependence of the refined lattice parameters on the zinc content. In contrast, the sample with a nominal zinc contentx= 0.3 shows the formation of a small amount of aurichalcite (Zn,Cu)5(OH)6(CO3)2as an additional phase. Based on the lattice parameter variations, the zinc content of the zincian malachite component in this sample is estimated to bex≈︁ 0.27, which seems to represent the maximum possible substitution in zincian malachite under the synthesis conditions applied. The results are discussed in relation to preparation of Cu/ZnO catalysts and the crystal structures of the minerals malachite and rosasite. One striking difference between these two structurally closely related phases is the orientation of the Jahn–Teller elongated axes of the CuO6octahedra in the unit cell, which seems to be correlated with the placement of the monoclinicβangle. The structural and chemical relationship between these crystallographically distinct phases is discussed using a hypothetical intermediate Zn2(OH)2CO3phase of higher orthorhombic symmetry. In addition to the crystallographic analysis, optical spectroscopy proves to be a useful tool for estimation of the Cu:Zn ratio in (Cu1–xZnx)2(OH)2CO3samples.