Synthesis and crystal structure of C2/c Ca(Co,Mg)Si₂O₆ pyroxenes: effect of the cation substitution on cell volume

Abstract

A series of clinopyroxenes along the CaMgSi2O6–CaCoSi2O6 join was synthesized by quenching from melts at 1500°C and subsequent annealing at 1250°C (at 0.0001 GPa). This protocol proved to be the most effective to obtain homogenous, impurity-free and stoichiometric pyroxenes. Electron microprobe analyses in energy dispersive mode were conducted and single-crystal X-ray diffraction data were collected on Ca (CoxMg1-x)Si2O6 pyroxenes with x = 0.2, 0.4, 0.5, 0.6. Effects of cation substitution at the M1 site are described. The experimental findings of this study allow us to extend the comparative analysis of the structural features of pyroxenes with divalent cations at the M1 and M2 sites.

High‐pressure Raman spectroscopy of Ca(Mg,Co)Si2O6 and Ca(Mg,Co)Ge2O6 clinopyroxenes

“…The high effect on the Raman peak positions of small changes in interatomic distances in tetrahedra, hardly detected in the structure refinements based on high-pressure single-crystal X-ray diffraction data, was observed also in the orthopyroxene enstatite. [43] The same is found for pyroxenes of the series CaMgSi 2 O 6 ─CaCoSi 2 O 6 , where the structural changes in the tetrahedron are negligible by single-crystal X-ray diffraction, [45] and the tetrahedral bond lengths appear to be unchanged in all the series. The strong changes in higher wavenumber modes have been related only to small differences in the tetrahedral distortion.…”

“…The same is found for pyroxenes of the series CaMgSi 2 O 6 ─CaCoSi 2 O 6 , where the structural changes in the tetrahedron are negligible by single‐crystal X‐ray diffraction, and the tetrahedral bond lengths appear to be unchanged in all the series. The strong changes in higher wavenumber modes have been related only to small differences in the tetrahedral distortion …”

Synthesis and Characterizations of (CoxMg(2−x))SiO4 Forsterite Ceramic Pigments from Mirror Waste

“…It could be implied that the d-spacing of unit cell increased because of the greater Co ion diffusion into the structure. The changes of unit cell volume with different Co content were observed in related compounds such as CaCoSi 2 O 6 pyroxenes [ 11 , 12 ] as well. However, when the content of Co was increased to x = 0.8–1.6, the XRD patterns exhibit the Co 2 SiO 4 phase which matched to JCPDF 00-015-0865, labeled “CS” in Figure 3 d. In addition, peak intensity of this phase reduced.…”

A comprehensive study of the magnetic properties of the pyroxenes series CaMgSi2O6–Co2Si2O6 as a function of Co content

“…The M1-subseries were synthesized at ambient pressure, heated in a muffle furnace at 1500 °C for 2 h and then quenched down to room temperature to obtain amorphous products. Such products were re-annealed at 1250 °C, until the crystallization process was complete, as reported in Gori et al [35]. All the samples look like tiny pink crystals with slightly different shades but without spurious phases.…”

“…The Co pyroxenes structure, stability and crystal field were discussed in previous papers [31][32][33][34][35] [36] and CaCoSi 2 O 6 [28]. In CaCoSi 2 O 6 , a negative Curie-Weiss temperature was found and a transition to an antiferromagnetic structure at 10 K was observed.…”