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  • 1
    Publication Date: 2020-03-23
    Description: Samples of the Cu2Cd x Zn1−x SnS4 solid solution series were synthesized by a mechanochemical process, exhibiting high crystallinity due to an annealing step under flowing H2S gas. The composition-dependent structural transition between the kesterite- and stannite-type phases was determined for Cd content close to x Cd ≈ 0.4 by means of x-ray diffraction and Raman spectroscopic probes, in excellent agreement with earlier investigations. Our DFT calculations predicted a critical Cd concentration value of x Cd = 0.5 as the 'border' between the stannite- and kesterite-type structure in the Cu2Cd x Zn1−x SnS4 solid solution series. The somewhat higher calculated Cd content value compared to the experimental case can be accounted by partial Cu/Zn disorder present in the synthesized samples. The measured optical band gaps E g of the Cu2Cd x Zn1−x SnS4 solid solution series decrease by ~0.3 eV upon immediate introduction of Cd into the lattice, with E g being almost constant with varying Cd concentration. All of our observations are interpreted within the framework of earlier reports on composition-dependent kesterite-to-stannite transition, where local structural variations due to the Zn2+ substitution by the larger Cd2+ cations appear to dictate the transition process.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 2
    Publication Date: 2021-07-28
    Description: We have investigated the high-pressure structural and vibrational behavior of the disordered kesterite-type Cu2ZnSnS4 compound at ambient temperature. Our experimental and theoretical investigations have revealed a clear structural transition to a GeSb-type phase close to 15 GPa, a tetragonally distorted variant of the NaCl-type phase. The latter transformation is accompanied by a cationic coordination increase from fourfold to sixfold with respect to the sulfur anions. In addition, a change in the compressibility rate was detected at about 8 GPa within the pressure stability range of the disordered kesterite-type phase. Upon decompression, a disordered zinc blende/sphalerite structure is recovered. We discuss our findings in close conjunction with our recent high-pressure work on the ordered Cu2ZnSnS4 modification.
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  • 3
    Publication Date: 2020-02-12
    Description: We have performed structural investigations of ordered kesterite-type Cu2ZnSnS4 up to 30 GPa. Our current X-ray diffraction results clearly excluded the presence of a kesterite → disordered kesterite transition reported previously between 7 and 9 GPa. Nevertheless, specific anomalies connected with the Cu-S bond length of the starting kesterite-type phase are evidenced close to 6 GPa, indicating subtle structural effects at play in this system. Moreover, we have indexed the high-pressure modification of Cu2ZnSnS4 adopted above 16 GPa to a disordered GeSb-type structure, a tetragonally distorted rocksalt-type modification. Full decompression leads to the adoption of a disordered sphalerite/zincblende-type structure. Our complementary density functional theory calculations reproduce accurately the experimental observations and indicate the possibility of a metallic high-pressure GeSb-type phase, unlike the starting semiconducting kesterite-type Cu2ZnSnS4 structure.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 4
    Publication Date: 2022-01-26
    Description: We carried out first-principles calculations to simulate Ag2ZnSnS4 and Ag2CdSnS4 and calculated enthalpies of different plausible structural models (kesterite-type, stannite-type, wurtzkesterite-type, wurtzstannite-type, and GeSb-type) to identify low- and high-pressure phases. For Ag2ZnSnS4, we predict the following transition: kesterite-type→[8.2GPa]→ GeSb-type. At the transition pressure, the electronic structure changes from semiconducting to metallic. For Ag2CdSnS4, we cannot decide which of the experimentally observed structures (kesterite-type or wurtzkesterite-type) is the ground-state structure because their energy difference is too small. At 4.7 GPa, however, we predict a transition to the GeSb-type structure with metallic character for both structures. Regarding the sensitivity of the material to disorder, a major drawback for solar cell applications, Ag2CdSnS4 behaves similar to Cu2ZnSnS4, both showing a high tendency to cationic disorder. In contrast, the disordered structures in Ag2ZnSnS4 are much higher in energy, and therefore, the material is less affected by disorder.
    Language: English
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  • 5
    Publication Date: 2024-01-09
    Description: Quaternary kesterite-type (KS) compounds have attracted worldwide attention from the scientific community as promising materials for solar cells. On the route to optimizing their performance, the effect of stress and strain constitutes a critical factor when it comes to thin film applications. Following a recent theoretical study, we report here joint experimental and computational high-pressure investigations on the KS Ag2ZnSnS4 and wurtz–kesterite (WZ–KS)-type Ag2CdSnS4 compounds. Our results reveal that both materials undergo successive transformations, first into a GeSb-type and then toward a CrN-type modification at ambient temperature. Our theoretical calculations predict a metallic character for all Ag2ZnSnS4 and Ag2CdSnS4 high-pressure phases. In addition, structural disorder is observed in KS Ag2ZnSnS4 upon moderate compression, prior to its KS → GeSb-type transition. Decompression leads to the recovery of a disordered zinc blende-type structure in the latter, whereas Ag2CdSnS4 retains the disordered GeSb-type modification. The similarities and deviations from the archetypical KS Cu2ZnSnS4 are discussed.
    Language: English
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