(Fe,Ni)2P allabogdanite can be an ambient pressure phase in iron meteorites

Abstract

An orthorhombic modification of (Fe,Ni) 2 P, allabogdanite, found in iron meteorites was considered to be thermodynamically stable at pressures above 8 GPa and temperatures of 1673 K according to the results of recent static high-pressure and high-temperature experiments. A hexagonal polymorphic modification of (Fe,Ni) 2 P, barringerite, was considered to be stable at ambient conditions. Experimental investigation through the solid-state synthesis supported by ab initio calculations was carried out to clarify the stability fields of (Fe,Ni) 2 P polymorphs. Both experimental and theoretical studies show that fe 2 P-allabogdanite is a low-temperature phase stable at ambient conditions up to a temperature of at least 773 K and, therefore, is not necessarily associated with high pressures. This is consistent with the textural relationships of allabogdanite in iron meteorites. Fe 2 P plays a substantial role in the mineralogy of iron meteorites. Two polymorphic modifications of Fe 2 P−Ni 2 P solid-solution currently known are hexagonal barringerite (C22) 1,2 and orthorhombic allabogdanite (C23) 3,4. Barringerite was discovered in the Ollague pallasite found in Bolivia 1. The composition determined by electron probe microanalysis was (Fe 0.58 Ni 0.42 Co 0.003) 1.95 P. It is isostructural with the hexagonal modification of Fe 2 P with lattice parameters a = 5.87(7) Å and c = 3.44(4) Å. In a short time after its discovery, it was shown that the Ollague meteorite is a fragment of a very large, up to several hundred kilograms, Imilac pallasite, the numerous fragments of which were found in the province of Antofagasta, Chile. It turned out that the Ollague meteorite was artificially reheated, which could cause high-temperature changes in the chemical and mineral compositions 5. It is noteworthy that barringerite has never been observed in other fragments of the Imilac meteorite or other investigated pallasites. Some barringerite findings are associated with placers 6 , but their sources are probably cosmogenic 2. Detailed mineralogical and crystal-chemical characterization of terrestrial barringerite from pyrometamorphic rocks of the Hatrurim formation, Israel is reported by Britvin et al. 2. The mineral occurs in associations of the so-called «paralavas» − initially silicate-carbonate sedimentary rocks that remelted during pyrometamorphic processes at about 1300 K, but under low pressure. Barringerite from the Hatrurim formation is almost pure Fe 2 P, the exact composition is (Fe 1.95 Ni 0.03 Cr 0.02) 2.00 P. The unit cell parameters determined by single crystal X-ray diffraction are a = 5.867(1) Å and c = 3.464(1) Å with Z = 3. The orthorhombic modification of Fe 2 P−Ni 2 P solid-solution, allabogdanite was first detected in anomalous Onello high-Ni ataxite found in 1997 in the alluvium of the Onello River, Yakutia, Russia 3. Earlier this mineral in the Onello ataxite was considered barringerite 7-9. The unit cell parameters of allabogdanite refined from single-crystal data are a = 5.792(7) Å, b = 3.564(4) Å, and c = 6.69...

Efficient Iron Phosphide Catalyst as a Counter Electrode in Dye-Sensitized Solar Cells

“…The characteristic Raman signature peaks of Fe 2 P appear at 164, 187, and 205 cm –1 and those of the FeP phase at 194, 211, 254, 296, and 303 cm –1 . These results coincide with the reported Raman shifts for Fe 2 P and FeP phases. , …”

“…These results coincide with the reported Raman shifts for Fe 2 P and FeP phases. 39,40 The obtained iron phosphide particles were dispersed in CHCl 3 and coated onto FTO substrates to use them as CE catalysts in DSSCs. The transmittance spectra of FeP, Fe 2 P, and Pt coated FTO films are shown in Figure 1d.…”

Alkali Metal (Li, Na, and K) Orthocarbonates: Stabilization of sp3-Bonded Carbon at Pressures above 20 GPa

“…The high-temperature phase P 6̅2 m is isotypic to the barringerite, and the Pnma → P 6̅2 m transition in the Na 2 O and K 2 O systems has a strict analogy to the allabogdanite → barringerite transition in the Fe 2 P and Co 2 P systems. − …”

Natural and experimental high-pressure, shock-produced terrestrial and extraterrestrial materials

“…The mineral was regarded to be a high-pressure polymorph of barringerite that is stable above 6 GPa and 900 °C based on previous high-pressure experiments (Dera et al 2008) and natural occurrences in several other iron meteorites (Britvin et al 2019). However, further detailed experimental and theoretical studies clarified that the mineral is also stable at ambient pressure below 500 °C (Litasov et al 2020). Hence, the results suggest a possibility that the formation of allabogranite in iron meteorites does not require shock metamorphism.…”