Synthesis and high-pressure transformation of metastable wurtzite-structured CuGaS2 nanocrystals

Abstract

The metastable wurtzite nanocrystals of CuGaS(2) have been synthesized through a facile and effective one-pot solvothermal approach. Through the Rietveld refinement on experimental X-ray diffraction patterns, we have unambiguously determined the structural parameters and the disordered nature of this wurtzite phase. The metastability of wurtzite structure with respect to the stable chalcopyrite structure was testified by a precise theoretical total energy calculation. Subsequent high-pressure experiments were performed to establish the isothermal phase stability of this wurtzite phase in the pressure range of 0-15.9 GPa, above which another disordered rock salt phase crystallized and remained stable up to 30.3 GPa, the highest pressure studied. Upon release of pressure, the sample was irreversible and intriguingly converted into the energetically more favorable and ordered chalcopyrite structure as revealed by the synchrotron X-ray diffraction and the high-resolution transmission electron microscopic measurements. The observed phase transitions were rationalized by first-principles calculations. The current research surely establishes a novel phase transition sequence of disorder → disorder → order, where pressure has played a significant role in effectively tuning stabilities of these different phases.

Electronic structure and photocatalytic activity of wurtzite Cu–Ga–S nanocrystals and their Zn substitution

“…In fact, the common formula Cu I B III C VI 2 is only valid for stoichiometric compounds where the Cu:Ga ratio is 1:1. 26,29 To synthesize the gallium-rich wurtzite Cu−Ga−S ternary nanocrystals, Cu:Ga ratios targeting 1:3 and 1:5 gave an average Cu:Ga composition of 1:2.1 and 1:4.1, respectively. The gallium-rich ternary Cu-Ga-S with the formula CuGa 2.1 S 3.7 and CuGa 4.1 S 6.7 were obtained (these actual formula are used hereafter).…”

“…Many CdS-based photocatalysts have been employed and thoroughly investigated since the 1980s, [7][8][9][10][11][12][13][14][15][16][17] and the ternary and the quaternary metal sulfides have been recently investigated, providing additional variety in selection of elements and resultant tunable bandgaps. [18][19][20][21][22][23][24][25][26][27][28][29][30][31] The synthesis of ternary copper gallium sulfide-based nanocrystals has attracted much attention in recent years because they are more environmentally benign than their Cd-or Pb-based counterparts. 21 Moreover, they have a promising potential for many applications such as photovoltaic, lightemitting devices, radiation detection, and photocatalysis.…”

“…23,26,32 The synthesis of wurtzite Cu−Ga−S nanocrystals remains challenging because of its metastable structure. 29,30 In this work, stoichiometric CuGaS 2 and gallium-rich nanocrystals were synthesized by employing a facile hot injection method: the recently-reported technique for CuIn x Ga 1−x S 2 , 27 and CuGa 2 In 3 S 8 nanocrystals. 31 Especially Wang et al successfully synthesized the monodisperse wurtzite CuIn x Ga 1−x S 2 nanocrystal including stoichiometric CuGaS 2 .…”

“…21 Moreover, they have a promising potential for many applications such as photovoltaic, lightemitting devices, radiation detection, and photocatalysis. 4,29 Commonly, ternary Cu−Ga−S materials with the thermodynamically preferred chalcopyrite crystal structure, which contains an ordered array of cations in the sublattice positions, are encountered during the synthesis. 23,26,32 The synthesis of wurtzite Cu−Ga−S nanocrystals remains challenging because of its metastable structure.…”

Enhanced performance of solar cells via anchoring CuGaS2 quantum dots

“…CuGaS 2 nanocrystals exhibit excellent activity in solar water splitting [42,43], biological and chemical sensing [44,45]. Ascribing to its wide band gap energy (2.2-2.5 eV) [46,47] corresponding to the green light region and direct transition [29,[48][49][50][51], CuGaS 2 nanocrystals could be an optimum candidate for the QDSSCs. However, very few studies on CuGaS 2 QDSSCs were reported.…”