Short-Range Order of Methylammonium and Persistence of Distortion at the Local Scale in MAPbBr3 Hybrid Perovskite.

Short-range investigation by means of variable-temperature neutron total scattering and pair distribution function analysis revealed that the local environment around the methylammonium (MA) cation in MAPbBr3 hybrid perovskite is maintained through the different phase transitions observed as a function of temperature. In addition, the orthorhombic distortion of the lattice is present at any temperature. Local structure around MA changes from static to configurationally averaged or dynamic with temperature but the local structure of the low-temperature orthorhombic phase is preserved.

Very strong hydrogen bonds in a bent chain structure of fluorohydrogenate anions in liquid Cs(FH)2.3F.

The structure of liquid Cs(FH)(2.3)F was revealed using a combination of high-energy x-ray and neutron diffraction measurements. We found that the strongest intermolecular H-F hydrogen bonds at an average distance of 1.36 A are accompanied by the formation of a high degree of bending of the oligomer chain in the melt, with [angle]FHF=150 degrees . A reverse Monte Carlo simulation showed that the average number of atoms per chain is 4.4. A detailed chain analysis of the atomic configuration revealed that (FH)(2)F(-) oligomer chains are the major entities in the liquid, and asymmetrical FHF(-) are formed owing to the strong H-F hydrogen bonds. The results suggest that an average of one or two HF molecules bond to each of the 11 fluorine atoms surrounding a cesium ion.