Cu2ZnSbS4: A Thioantimonate(V) with Remarkably Strong Covalent Sb-S Bonding.

A new member to the A2IBIICIVX4 compound family, Cu2ZnSbS4, was synthesized successfully using ball milling and postannealing in H2S-atmosphere. For comparative purposes, Cu3SbS4 was additionally prepared using the same synthetic approach. As is common for A2IBIICIVX4 compounds, Cu2ZnSbS4 crystallizes isostructural to Cu3SbS4 in the stannite-type structure in space group I42m. Both antimony sulfides contain monovalent diamagnetic copper and are characterized by substantial covalent bonding. This is consistent with the 121Sb isomer shifts occurring for the Mössbauer spectra of Cu2ZnSbS4 (-7.71 mm s-1) and Cu3SbS4 (-7.68 mm s-1) which fall in the region of covalently bonded Sb(V) compounds. These spectroscopic results are supported by electronic structure calculations.

High-Pressure Behavior and Disorder for Ag2ZnSnS4 and Ag2CdSnS4.

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.

Mechanochemical Synthesis and Magnetic Characterization of Nanosized Cubic Spinel FeCr2S4 Particles.

Nanosized samples of the cubic thiospinel FeCr2S4 were synthesized by ball milling of FeS and Cr2S3 precursors followed by a distinct temperature treatment between 500 and 800 °C. Depending on the applied temperature, volume weighted mean (L vol) particle sizes of 56 nm (500 °C), 86 nm (600 °C), and 123 nm (800 °C) were obtained. All samples show a transition into the ferrimagnetic state at a Curie temperature T C of ∼ 167 K only slightly depending on the annealing temperature. Above T C, ferromagnetic spin clusters survive and Curie-Weiss behavior is observed only at T ≫ T C, with T depending on the heat treatments and the external magnetic field applied. Zero-field-cooled and field-cooled magnetic susceptibilities diverge significantly below T C in contrast to what is observed for conventionally solid-state-prepared polycrystalline samples. In the low-temperature region, all samples show a transition into the orbital ordered state at about 9 K, which is more pronounced for the samples heated to higher temperatures. This observation is a clear indication that the cation disorder is very low because a pronounced disorder would suppress this magnetic transition. The unusual magnetic properties of the samples at low temperatures and different external magnetic fields can be clearly related to different factors like structural microstrain and magnetocrystalline anisotropy.