Organic−inorganic tin(II) halide perovskites have emerged as promising alternatives to lead halide perovskites in optoelectronic applications. While they suffer from considerably poorer performance and stability as compared to their lead analogues, their performance improvements have so far largely been driven by trial and error efforts due to a critical lack of methods to probe their atomic-level microstructure. Here, we identify the challenges and devise a 119Sn solid-state NMR protocol for the determination of the local structure of mixed-cation and mixed-halide tin(II) halide perovskites as well as their degradation products and related phases. We establish that the longitudinal relaxation of 119Sn can span 6 orders of magnitude in this class of compounds which makes judicious choice of experimental NMR parameters essential for reliable detection of various phases. We show that Cl/Br and I/Br mixed-halide perovskites form solid alloys in any ratio, while only limited mixing is possible for I/Cl compositions. We elucidate the degradation pathways of Cs-, MA- and FA-based tin(II) halides and show that degradation leads to highly disordered, qualitatively similar prod-ucts, regardless of the A-site cation and halide. We detect the presence of metallic tin amongst the degradation products, which we suggest could contribute to the previously report-ed high conductivities in tin(II) halide perovskites. 119Sn NMR chemical shifts are a sensitive probe of the halide co-ordination environment as well as of the A-site cation com-position. Finally, we use variable-temperature multi-field relaxation measurements to quantify ion dynamics in MASnBr3, establish activation energies for motion and show that this motion leads to spontaneous halide homogenization at room temperature whenever two different pure-halide perovskites are put in physical contact.

Carbon supported Pt nanoparticles with diameters ranging from 2 to 28 nm have been studied using X-ray diffraction. The unit cell parameter of synthesized Pt/C nanoparticles is always lower than that of bulk Pt. By decreasing the average particle size D to approximately 2 nm, the unit cell parameter a nonlinearly decreases by about 0.03 Å which corresponds to a variation of 0.7% in comparison to bulk Pt, and the size effect is predominant for sizes ranging from 2 to 10 nm. The dependence a(1/D) is approximated well using a straight line with a slope of −0.0555 ± 0.0067 nm⁻¹ and an intercept of −3.9230 ± 0.0017 Å. For interpreting the obtained experimental dependence of the unit cell parameter of Pt/C nanoparticles, four different theoretical approaches such as the thermal vacancy mechanism, continuous-medium model, Laplace pressure, and bond order–length–strength correlation mechanism, were used. Comparison of the calculated dependencies, based on the above models, with the experimental ones, shows that the continuous-medium model agrees best with the experimentally found unit cell parameter dependence of our carbon supported Pt nanoparticles.