Vacancy ordering and lithium insertion in III2VI3 nanowires

Abstract

Superlattice structures resulting from vacancy ordering have been observed in many materials. Here we report vacancy ordering behavior in 2 3 nanowires. The formation of layer-like structural vacancies has been achieved during the synthesis of In 2 Se 3 nanowires through a vapor-transport route. Doping In 2 Se 3 nanowires with small amounts of Ga during synthesis can completely change the structural vacancy ordering from a layer-like to a screw-like pattern for (In x Ga 1 x ) 2 Se 3 nanowires. Lithium atoms can fi ll in the layer-like structural vacancies of In 2 Se 3 nanowires and generate new types of vacancy and lithium atom ordering superlattices. The screw-patterned vacancies of (In x Ga 1 x ) 2 Se 3 nanowires show reversible lithium insertion. Our results contribute to the understanding of structure property correlations of 2 3 materials used in lithium ion storage, photovoltaics, and phase change memory. KEYWORDSNanowire (NW), vacancy ordering, superlattice, , lithium insertion Vacancies are a classical point defect and play an important role in atomic diffusion, doping, and color centers in ionic crystals. Vacancy ordering phenomena have been investigated in nonstoichiometric bulk materials including oxides [1 3], chalcogenides [4 6], carbides [7, 8], silicides [9], and nitrides [10]. The ability to arrange vacancies is important for gaining control over material properties. For example, oxygen vacancy ordering in transition metal oxides has been shown to affect their ferroelectric properties and hightemperature superconductivity [11, 12]; intercalation materials such as Li x TiS 2 , Li x TaS 2 , and Li x CoO 2 have been shown to form superlattice structures upon Li deintercalation, which is due to lithium and vacancy ordering and is critical to the structure stability and kinetics of Li-ion battery electrodes [13 16]; the ordered vacancy compound at the CuIn(Ga)Se 2 CdS interface has different electrical properties from CuIn(Ga)Se 2 and is believed to play an important role in the high effi ciency of CuIn(Ga)Se 2 solar cells [5, 17, 18]. The semiconductors have attracted attention because of their unique structural, optical, and electrical properties, which result in applications including lithium ion batteries [19, 20], photovoltaics [21 23], and phase-change memory [24, 25]. Owing to the mismatch between and atoms, bulk compounds show a variety of crystal polymorphism Nano Res (Nano Research depending on the growth conditions. We and others have recently developed the synthesis of single crystalline In 2 Se 3 [26, 27] and GaSe [28] nanowires (NWs) because NW morphology not only provides the opportunity to engineer materials for better device performance in applications such as transistors [29 31], solar cells [32 33], nanogenerators [34], batteries [35 37], and memory devices [38 40], but also affords well-defined nanoscale domains in which to correlate structure and properties [41,42]. We have observed a metal-to-insulator transition in In 2 Se 3 NWs, which correlated with a four-fold superlattice-to-...

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