Raman Spectroscopic Studies of Pyrite at High Pressure and High Temperature

Juan Chen,Shuhang Shuai,Jingjing Wan,Mengxue Zhang,Yi Yuan,Heping Li

doi:10.3390/min12030332

Abstract

Variations in the Raman spectra of pyrite were studied from 113 to 853 K at room pressure with a Linkam heating and freezing stage, and for 297–513 K and pressures up to 1.9 GPa with a hydrothermal diamond anvil cell. All observed frequencies decreased continuously with an increase in temperatures up to 653 K at ambient pressure. Hematite began to form at 653 K, all pyrite had transformed to hematite (H) at 688 K, and the hematite melted at 853 K. An increase in temperature at every initial pressure (group 1: 0.5 GPa, group 2: 1.1 GPa, group 3: 1.7 GPa, group 4: 1.9 GPa), showed no evidence for chemical reaction or pyrite decomposition. Two or three Raman modes were observed because of crystal orientation or temperature-induced fluorescence effects. The pressure groups showed a decreasing trend of frequency with gradual heating. The interaction of pressure and temperature led to a gradual decrease in Ag and Eg mode at a lower pressure (0.5 GPa and 1.1 GPa) than other pressure groups. Pressure and temperature effects are evident for groups 1 and 2; however, for groups 3 and 4, the temperature shows a larger effect than pressure and leads to a sharp decrease in Ag and Eg modes.

Highlights

The most common sulfide mineral pyrite FeS2, which is common in ore deposits and results in acid mine drainage because of its specific physical and chemical properties, has attracted the interest of many researchers in the high-pressure and high-temperature field.As with NaCl, pyrite has a cubic structure, with a non-symmorphic space groupTh (Pa3) and four formula units per unit cell
When the Raman signals of pyrite were excited by the 514.5-nm line of an argon-ion laser, the assignment of all Raman modes included Eg: 344 cm−1, Tg(1): 350 cm−1, Tg(2): 377 cm−1, Ag: 379 cm−1, and Tg(3): 430 cm−1, which is a typical structure of anisotropic pyrite, according to Kleppe and Jephcoat [2]
Ag, were observed, which depended on crystal orientation assignment of pyrite is given in Table

Summary

Introduction

The most common sulfide mineral pyrite FeS2 , which is common in ore deposits and results in acid mine drainage because of its specific physical and chemical properties, has attracted the interest of many researchers in the high-pressure and high-temperature field.As with NaCl, pyrite has a cubic structure, with a non-symmorphic space groupTh (Pa3) and four formula units per unit cell. As with NaCl, pyrite has a cubic structure, with a non-symmorphic space group. According to group (Pa3) theory, the irreducible representation of FeS2 vibrations is expressed as. Г = Ag + Eg + 3Tg + 2Au + 6Tu, and the Ag + Eg + 3Tg represents five Raman active modes [1]. These expressions indicate that one mode is (Ag, S–S in phase stretch) symmetric and one is doubly degenerate (Eg, S2 librational mode), and the third is triply degenerate (Tg, Tg(1) and Tg(3) are coupled librational and stretching modes with Tg(2) being the. When the Raman signals of pyrite were excited by the 514.5-nm line of an argon-ion laser, the assignment of all Raman modes included Eg: 344 cm−1 , Tg(1): 350 cm−1 , Tg(2): 377 cm−1 , Ag: 379 cm−1 , and Tg(3): 430 cm−1 , which is a typical structure of anisotropic pyrite, according to Kleppe and Jephcoat [2]

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