The study of Raman spectroscopy and the crystal structure of synthetic yimengite

Abstract

Introduction: As a result of previous experiments in the system chromite-ilmenite-K2CO 3–H2O-CO2 at 5 GPa and 1200 °C, yimengite-potassium mineral of the magnetoplumbite group, was obtained in association with minerals of the hollandite and crichtonite groups. The Raman spectroscopy was studied and the structure of yimengite was deciphered. Methods: Mineral compositions were determined using a CamScan MV2300 (VEGA TS 5130MM) electron microscope with a Link INCA Energy energy dispersive microanalyzer. The presence of potassium phases of the magnetoplumbite, crichtonite, and hollandite groups was also confirmed by studies of their Raman spectra obtained using a Raman spectrometer Renishaw RM1000 equipped with a Leica microscope (Korzhinsky’s Institute of Experimenta Minera ogy Of the Russian Academy of Sciences, Chernogolovka).The crystal structure of synthetic yimengite was determined for the single crystal based on the results of low-temperature (T=90 K) X-ray diffraction experiment carried out at the Belok/RSA station (λ=0.74539A) of Kurchatov Synchrotron Radiation Source (Kurchatov Institute National Research Centre, Moscow). Results and discussions: The structure of a potassium compound from the magnetoplumbite group with the chemical formula K0.90Ti5.16Cr2.94Fe2.54Mg0.87Al0.22Mn0.30O19 was investigated. The crystal was extracted from the products of the experiment in the chromite–i menite system − K2CO3 – H2O-CO2at 5 GPa and 12000С. The parameters of the hexagonal cell were obtained: a=5.8920(2), c=23.0113(8) Ȧ, sp. gr. P63/mmc, Z = 4. The studied compound was isostructural to yimengite. In contrast to yimengite, the studied phase was dominated by Fe²⁺ , which was distributed between the tetrahedral M3 and octahedral M5 positions. The absence of Fe³⁺ in the studied compound caused the incorporation of Cr and a small amount of Al into M1 (octahedron) and M2 (trigonal bipyramid) positions. The Raman spectroscopy of yimengite was studied. Conclusions: The results of the study of synthetic yimengite expand the understanding of variations in the distribution of A (K, Ba) and M-cations (Ti, Cr, Fe, Mg, Al, Mn) at different positions in minerals with the magnetoplumbite structural type.