0000000000164477
AUTHOR
Monika Koch-müller
Synthesis of a quenchable high-pressure form of magnetite (h-Fe3O4) with composition Fe1(Fe2+0.75Mg0.26)Fe2(Fe3+0.70Cr0.15Al0.11Si0.04)2O4
We report the synthesis of h-magnetite, ideally h-Fe 3 O 4 with considerable amounts of substitutional cations (Cr, Mg, Al, Si) and quenchable to ambient conditions. Two types of experiments were performed at 18 GPa and 1800 °C in a multi-anvil press. In one, we used an oxide mixture with a majoritic stoichiometry Mg 1.8 Fe 1.2 (Al 1.4 Cr 0.2 Si 0.2 Mg 0.2 )Si 3 O 12 , with Si and Mg in excess as starting material (MA-367, MA-380). In the second type of experiment (MA-376), we started from an oxide mixture on the composition of the Fe-oxide phase obtained in MA-367. The Fe-oxide phases of both experiments were investigated by electron microprobe and transmission electron microscopy includin…
High-pressure crystal structure investigation of synthetic Fe2SiO4 spinel.
AbstractThe crystal structure of Fe2SiO4 spinel at room temperature was investigated at seven different pressures by X-ray diffraction, using a diamond anvil cell to examine the influence of Fe substitution on ringwoodite behaviour at high pressure. The results compared with those of a pure Mg endmember show that the substitution of Fe into the spinel structure causes only small changes in the compression rate of coordination polyhedra and the distortion of the octahedron. The data show that the compression rate for the octahedron and tetrahedron in (Mg,Fe)2SiO4 can be considered statistically equal for FeO6 and MgO6, as well as for SiO4 in both the endmembers. This shows why almost identic…
Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6
The ferroelectric to paraelectric phase transition of multiferroic ${\mathrm{CaMnTi}}_{2}{\mathrm{O}}_{6}$ has been investigated at high pressures and ambient temperature by second-harmonic generation (SHG), Raman spectroscopy, and powder and single-crystal x-ray diffraction. We have found that ${\mathrm{CaMnTi}}_{2}{\mathrm{O}}_{6}$ undergoes a pressure-induced structural phase transition ($P{4}_{2}mc\ensuremath{\rightarrow}P{4}_{2}/nmc$) at $\ensuremath{\sim}7\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ to the same paraelectric structure found at ambient pressure and ${T}_{c}=630\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The continuous linear decrease of the SHG intensity that disappears at 7 …