Vapor growth and characterization of pyrite (FeS2) doped with Co, Ni, and As: Variations in semiconducting properties

Pyrite (FeS2) crystals doped with As, Ni and Co were synthesized with chemical vapor transport over an 18 cm horizontal gradient of 700-600 degrees C in evacuated quartz tubes, from a mixture of Fes and S, with FeBr3 as a transport agent. Sulfur fugacity and thus S:Fe stoichiometry was constrained by the Fe1-xS/FeS2-y buffer. As, Ni and Co concentrations were similar to 3-800ppm, similar to 200-1500 ppm and 450-3700 ppm, respectively. Semiconducting properties were measured at room temperature using a van der Pauw and Hall measurement system. Ni and Co-doped pyrite are n-type while As-doped pyrite tends to be p-type. Resistivity for Co-doped pyrite ranged from 0.009 to 0.02 Omega cm while for Ni-and As-doped pyrite, resistivity ranged from 2 to 17 Omega cm. Undoped pyrite resistivity ranged from 15 to 85 Omega cm. Carrier concentration was similar for undoped and Ni-doped pyrite, ranging from 10(15) to 10(16.6) cm(-3), while for Co-doped pyrite it ranged from 1 01 S. 7 to 10(19.3) cm(-3) and for As-doped pyrite it ranged from 10(14) to 10(18) cm(-3). Hall mobility was similar for Co and Ni-doped pyrite ranging from 60 to 270 cm(2)v(-1) s(-1) while for undoped pyrite it ranged from 8 to 70 cm(2) v(-1) s(-1). Hall mobility for As-doped pyrite ranged from 55.0 to 0.2 cm(2) v(-1) s(-1) for electrons and from 0.1 to 11.3 cm(2) v(-1) s(-1) for holes with the exception of one sample (of 22). These values should be viewed more as trends than as definitive. The results obtained for Ni, Co, and undoped pyrite are similar to those reported in the literature while results for As-doped synthetic pyrite have not previously been reported. (c) 2005 Elsevier B.V. All rights reserved.