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

Malte Behrens (1) , Frank Girgsdies (2)

1 Department of Inorganic Chemistry [Berlin]
2 Department of Inorganic Chemistry [Berlin]

Synthetic zincian malachite samples (Cu1-xZnx)2(OH)2CO3 with x = 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 to x = 0.2 indicate single phase materials with an approximately linear dependence of the refined lattice parameters on the Zn content. In contrast, the sample with a nominal Zn content x = 0.3 shows the formation of a small amount of aurichalcite (Zn,Cu)5(OH)6(CO3)2 as an additional phase. Based on the lattice parameter variations, the Zn content of the zincian malachite component in this sample is estimated to be x  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 CuO6 octahedra in the unit cell, which seems to be correlated with the placement of the monoclinic  angle. The structural and chemical relationship between these crystallographically distinct phases is discussed using a hypothetical intermediate Zn2(OH)2CO3 phase 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)2CO3 samples.

Mots clés: Physical Sciences

Malte Behrens, Frank Girgsdies. Structural Effects of Cu,Zn Substitution in the Malachite–Rosasite System. Journal of Inorganic and General Chemistry / Zeitschrift für anorganische und allgemeine Chemie, 2010, ⟨10.1002/zaac.201000028⟩. ⟨hal-00552444⟩