Abstract
High energy ball milling is used to make first the quaternary sulfide Cu2ZnSnS4 raw nanopowders from two different precursor systems. The mechanochemical reactions in this step afford cubic pre-kesterite with defunct semiconducting properties and showing no solid-state 65Cu and 119Sn MAS NMR spectra. In the second step, each of the milled raw materials is annealed at 500 and 550 °C under argon to result in tetragonal kesterite nanopowders with the anticipated UV-Vis-determined energy band gap and qualitatively correct NMR characteristics. The magnetic properties of all materials are measured with SQUID magnetometer and confirm the pre-kesterite samples to show typical paramagnetism with a weak ferromagnetic component whereas all the kesterite samples to exhibit only paramagnetism of relatively decreased magnitude. Upon conditioning in ambient air for 3 months, a pronounced increase of paramagnetism is observed in all materials. Correlations between the magnetic and spectroscopic properties of the nanopowders including impact of oxidation are discussed. The magnetic measurements coupled with NMR spectroscopy appear to be indispensable for comprehensive kesterite evaluation.
Highlights
The quaternary sulfide Cu(1+) 2 Zn(2+) Sn(4+) S(2−) 4 called in short kesterite or CZTS has been a focus of intense research work for more than a decade because of its great potentials in the generation photovoltaics [1,2,3,4,5], and because of its very much elusive chemical and physical characteristics
Mechanochemically assisted synthesis of kesterite starting from two precursor systems, i.e., (i) previously explored by us [23] and others [29,30,31] mixture of the constituent elements Cu, Zn, Sn, and S (CE system), presently, at the highest achievable rotation speed of 1000 rpm, and (ii) a mixture of the selected metal sulfides Cu2 S, ZnS, SnS, and supplementary sulfur S (MS system), which to the best of our knowledge is reported for the first time
The XRD patterns for the nanopowders in the MS system are shown in Figure 1 and they can be satisfactorily compared with the respective patterns in the constituent element system (CE) system as previously reported by us [23]
Summary
The quaternary sulfide Cu(1+) 2 Zn(2+) Sn(4+) S(2−) 4 called in short kesterite or CZTS has been a focus of intense research work for more than a decade because of its great potentials in the generation photovoltaics [1,2,3,4,5], and because of its very much elusive chemical and physical characteristics. It is probable that depending on the strength of paramagnetism coupled with the characteristics of lattice disorder, some nuclei may, and some may not fulfill nuclear magnetic resonance conditions—not all nuclei could, be seen for this reason by NMR This has to be confronted with the observation that in the copper sulfide Cu2 S with the non-magnetic Cu1+ and. Cu1+ -ion low symmetry local environment and very large quadrupolar coupling constants resulted in significant second order quadrupolar interactions that broadened the resonance signal beyond detection It appears that in the structurally and electronically complex kesterite nanopowders the paramagnetic factor could be entangled in a complex way with nuclear magnetic resonance output, at the end both having relevance to the crucial kesterite’s semiconductor properties. 65 Cu and 119 Sn MAS NMR, energy states of elements were analyzed by XPS technique, whereas the crucial semiconductor characteristics were probed with UV-Vis spectroscopy
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