Rapid preparation and characterization of pyrite materials under HPHT: A new method

Abstract This paper reports the synthesis of bulk pyrite (FeS2) polycrystals at high pressure and high temperature (HPHT) for the first time. The HPHT method markedly improves the speed of synthesis, reducing the time for synthesizing bulk pyrite from several hundred hours to several hours. A unique honeycomb-type structure was introduced into the system by the primary reaction to refine the size of the reactants. On this basis, the sulfur-deficient contamination phase Fe7S8 was effectively eliminated by secondary synthesis. Using Raman spectroscopy and X-ray diffraction (XRD), the crystalline phase of the product was confirmed to be the cubic pyrite phase. The crystal structure and initial crystal parameters of pyrite crystals synthesized under HPHT conditions were obtained for the first time by Rietveld refinement with GASA software. In combination with a scanning electron microscope (SEM) assay, the reaction process was traced, and the significance of secondary synthesis for HPHT was analyzed. Seebeck data showed that as the temperature increased, the sample changed from p-type to an n-type semiconductor and the conductivity increased monotonically, revealing the typical semiconductor characteristics of pyrite. UV reflectance spectra and VSM tests revealed the bandgap width and magnetic properties of pyrite.