The metal sulfides exhibit a great diversity of electrical and magnetic properties with both scientific interest and practical applications. These properties apply major constraints on models of the electronic structure (or chemical bonding) in sulfides (Vaughan and Rosso 2006, this volume). The pure and doped synthetic equivalents of certain sulfide minerals have actual or potential applications in the electronics industries (optical devices, photovoltaics, photodiodes and magnetic recording devices). Sulfides are also components of many thin film devices and have been extensively investigated as part of the nanotechnology revolution. Certain electrical and magnetic properties of sulfide minerals mean they contribute to geomagnetism and paleo-magnetism, and provide the geophysical prospector with exploration tools for metalliferous ore deposits. To the mineral technologist, these same properties provide methods for the separation of the metal-bearing sulfides from associated waste minerals after mining and milling and before extraction of the metal by pyrometallurgical or hydrometallurgical treatment.

In this chapter, the theory and measurement of electrical and magnetic properties are outlined along with spectroscopic and diffraction studies that can provide insights into magnetic behavior are discussed. A brief review of electrical and magnetic studies of major sulfide minerals includes some examples of the applications of sulfide electrical and magnetic properties, including special consideration of the properties of sulfide nanoparticles. Most of the available data presented are for pure synthetic binary and ternary sulfides, as very small concentrations of impurities can dramatically affect electrical properties leading to problems of interpreting data from natural samples. Although data for several of the commonly found sulfides are discussed in this chapter, no attempt is made at a comprehensive coverage.

The section below on theory and measurement of electrical and magnetic properties draws on the account given in Vaughan and Craig (1978) to which readers are referred for further details. It …

Electrical and magnetic properties of sulfides

Mössbauer Spectroscopy of Minerals

Thermoelectric performance of the p-type semiconductor bornite, Cu5FeS4, is greatly enhanced through chemical substitution. Nonstoichiometric materials in which the Cu:Fe ratio and overall cation-vacancy content were adjusted are reported, and a figure of merit, ZT = 0.79, is achieved at temperatures as low as 550 K in Cu4.972Fe0.968S4. All materials were synthesized mechanochemically and characterized by powder X-ray diffraction, differential scanning calorimetry (DSC), and thermal and electrical transport property measurements. Single-phase behavior is retained in copper deficient phases, Cu5–xFeS4, for vacancy levels up to x = 0.1, while in materials Cu5+yFe1–yS4, in which the Cu:Fe ratio is varied while maintaining full occupancy of cation sites, single-phase behavior persists for y ≤ 0.08. Adjusting the Cu:Fe ratio at a constant cation-vacancy level of 0.06 in Cu4.94+zFe1–zS4, leads to single phases for z ≤ 0.04. DSC measurements indicate the temperature of the intermediate- (2a) to high-temperature ...

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High Thermoelectric Performance of Bornite through Control of the Cu(II) Content and Vacancy Concentration

Analysis of interfaces in Bornite (Cu5FeS4) fabricated Schottky diode using impedance spectroscopy method and its photosensitive behavior

Here we have reported the electric and dielectric properties of a Bornite (Cu5FeS4) film using non-destructive complex impedance spectroscopy (CIS) in the frequency range 40 Hz–20 MHz and bias voltage range 0–0.8 V. A typical hydrothermal reaction was carried out to obtain the Cu5FeS4 material. Thereafter, we fabricated the film of the synthesized material and analysed its various properties as a function of frequency and dc bias voltages. The CIS analysis at room temperature (303 K) for different forward dc bias voltages shows that the bulk resistance plays a predominant role in conduction mechanism. The complex impedance (Nyquist) plots are well modelled with grain and grain boundary resistance by introducing proper ac equivalent circuit. The impedance loss spectra showed that the relaxation peak shifts towards the higher frequency with increasing bias voltages, which implies the possibility of a charge hopping between the localized charge states. Furthermore, we find that dielectric constant (
 $${\varepsilon ^\prime }$$
 ), dielectric loss (
 $${\varepsilon ^{\prime \prime }}$$
 ), electrical modulus (
 $${{\text{M}}^*}$$
 ) and ac/dc conductivity of the Cu5FeS4 film are strongly frequency dependent. The values of $${\varepsilon ^\prime }$$
 and $${\varepsilon ^{\prime \prime }}$$
 decreases whereas ac conductivity increases with increasing frequency. High frequency and low frequency dielectric constant of the material are found to be 3.48 and in the order of 104 respectively. Electrical modulus study is introduced for better explanation of conductivity relaxation phenomenon. Finally, we investigated the variation of ac/dc conductivity with forward dc bias voltages. This confirmed the presence of a hopping mechanism for electrical transport in our system, which can be best explained on the basis of jump relaxation model. Overall, this extensive study based on complex impedance spectroscopy demonstrates the dielectric relaxation behaviour of Cu5FeS4 film and also shed light on hopping induced conduction mechanism.

Bias dependent conduction and relaxation mechanism study of Cu 5 FeS 4 film and its significance in signal transport network

Neutron powder diffraction techniques have been used to investigate the magnetic structure of bornite, Cu5FeS4. Below the antiferromagnetic ordering temperature of 76 ± 2 K extra peaks appear in the diffraction pattern corresponding to magnetic ordering. The data are consistent with an antiferromagnetic alignment of iron atoms with moments of 4.4 ± 0.3 μB on the iron sites proposed by Koto and Morimoto on the basis of X-ray measurements of the crystal structure. Mossbauer and neutron diffraction data suggest that the second magnetic phase transition at 8 K arises from a spin rotation. Since the magnetic structure gives only superexchange paths between iron atoms through two or more anions, it is difficult to understand why the Neel temperature is so high without invoking small moments on copper atoms

G. Longworth

Papers

Magnetic structure of bornite, Cu5FeS4